Cairo::Context Class Reference

Context is the main class used to draw in cairomm. More...

## Public Types

typedef cairo_t | cobject
| The base cairo C type that is wrapped by Cairo::Context. More...

## Public Member Functions

| Context (cairo_t*cobject, bool has_reference=false)
| Create a C++ wrapper for the C instance. More...
| Context (const Context&)=delete
Context& | operator= (const Context&)=delete
virtual | ~Context ()
void | save ()
| Makes a copy of the current state of the Context and saves it on an internal stack of saved states. More...
void | restore ()
| Restores cr to the state saved by a preceding call to save() and removes that state from the stack of saved states. More...
void | set_operator (Operator op)
| Sets the compositing operator to be used for all drawing operations. More...
void | set_source (const RefPtr< const Pattern >& source)
| Sets the source pattern within the Context to source. More...
void | set_source_rgb (double red, double green, double blue)
| Sets the source pattern within the Context to an opaque color. More...
void | set_source_rgba (double red, double green, double blue, double alpha)
| Sets the source pattern within the Context to a translucent color. More...
void | set_source (const RefPtr< Surface >& surface, double x, double y)
| This is a convenience function for creating a pattern from a Surface and setting it as the source. More...
void | set_tolerance (double tolerance)
| Sets the tolerance used when converting paths into trapezoids. More...
void | set_antialias (Antialias antialias)
| Set the antialiasing mode of the rasterizer used for drawing shapes. More...
void | set_fill_rule (FillRule fill_rule)
| Set the current fill rule within the cairo Context. More...
void | set_line_width (double width)
| Sets the current line width within the cairo Context. More...
void | set_line_cap (LineCap line_cap)
| Sets the current line cap style within the cairo Context. More...
void | set_line_join (LineJoin line_join)
| Sets the current line join style within the cairo Context. More...
void | set_dash (std::valarray< double >& dashes, double offset)
| Alternate version of set_dash(). More...
void | set_dash (std::vector< double >& dashes, double offset)
| Sets the dash pattern to be used by stroke(). More...
void | set_dash (const std::valarray< double >& dashes, double offset)
| Alternate version of set_dash(). More...
void | set_dash (const std::vector< double >& dashes, double offset)
| Sets the dash pattern to be used by stroke(). More...
void | unset_dash ()
| This function disables a dash pattern that was set with set_dash() More...
void | set_miter_limit (double limit)
| Sets the current miter limit within the cairo context. More...
void | translate (double tx, double ty)
| Modifies the current transformation matrix (CTM) by translating the user-space origin by (tx, ty). More...
void | scale (double sx, double sy)
| Modifies the current transformation matrix (CTM) by scaling the X and Y user-space axes by sx and sy respectively. More...
void | rotate (double angle_radians)
| Modifies the current transformation matrix (CTM) by rotating the user-space axes by angle radians. More...
void | rotate_degrees (double angle_degres)
| A convenience wrapper around rotate() that accepts angles in degrees. More...
void | transform (const Matrix& matrix)
| Modifies the current transformation matrix (CTM) by applying matrix as an additional transformation. More...
void | transform (const cairo_matrix_t& matrix)
void | set_matrix (const Matrix& matrix)
| Modifies the current transformation matrix (CTM) by setting it equal to matrix. More...
void | set_matrix (const cairo_matrix_t& matrix)
void | set_identity_matrix ()
| Resets the current transformation matrix (CTM) by setting it equal to the identity matrix. More...
void | user_to_device (double& x, double& y)
| Transform a coordinate from user space to device space by multiplying the given point by the current transformation matrix (CTM). More...
void | user_to_device_distance (double& dx, double& dy)
| Transform a distance vector from user space to device space. More...
void | device_to_user (double& x, double& y)
| Transform a coordinate from device space to user space by multiplying the given point by the inverse of the current transformation matrix (CTM). More...
void | device_to_user_distance (double& dx, double& dy)
| Transform a distance vector from device space to user space. More...
void | user_to_device (double& x, double& y) const
| Transform a coordinate from user space to device space by multiplying the given point by the current transformation matrix (CTM). More...
void | user_to_device_distance (double& dx, double& dy) const
| Transform a distance vector from user space to device space. More...
void | device_to_user (double& x, double& y) const
| Transform a coordinate from device space to user space by multiplying the given point by the inverse of the current transformation matrix (CTM). More...
void | device_to_user_distance (double& dx, double& dy) const
| Transform a distance vector from device space to user space. More...
void | begin_new_path ()
| Clears the current path. More...
void | begin_new_sub_path ()
| Begin a new subpath. More...
void | move_to (double x, double y)
| If the current subpath is not empty, begin a new subpath. More...
void | line_to (double x, double y)
| Adds a line to the path from the current point to position (x, y) in user-space coordinates. More...
void | curve_to (double x1, double y1, double x2, double y2, double x3, double y3)
| Adds a cubic Bezier spline to the path from the current point to position (x3, y3) in user-space coordinates, using (x1, y1) and (x2, y2) as the control points. More...
void | arc (double xc, double yc, double radius, double angle1, double angle2)
| Adds a circular arc of the given radius to the current path. More...
void | arc_negative (double xc, double yc, double radius, double angle1, double angle2)
| Adds a circular arc of the given radius to the current path. More...
void | rel_move_to (double dx, double dy)
| If the current subpath is not empty, begin a new subpath. More...
void | rel_line_to (double dx, double dy)
| Relative-coordinate version of line_to(). More...
void | rel_curve_to (double dx1, double dy1, double dx2, double dy2, double dx3, double dy3)
| Relative-coordinate version of curve_to(). More...
void | rectangle (double x, double y, double width, double height)
| Adds a closed-subpath rectangle of the given size to the current path at position (x, y) in user-space coordinates. More...
void | close_path ()
| Adds a line segment to the path from the current point to the beginning of the current subpath, (the most recent point passed to move_to()), and closes this subpath. More...
void | paint ()
| A drawing operator that paints the current source everywhere within the current clip region. More...
void | paint_with_alpha (double alpha)
| A drawing operator that paints the current source everywhere within the current clip region using a mask of constant alpha value alpha. More...
void | mask (const RefPtr< const Pattern >& pattern)
| A drawing operator that paints the current source using the alpha channel of pattern as a mask. More...
void | mask (const RefPtr< const Surface >& surface, double surface_x, double surface_y)
| A drawing operator that paints the current source using the alpha channel of surface as a mask. More...
void | stroke ()
| A drawing operator that strokes the current Path according to the current line width, line join, line cap, and dash settings. More...
void | stroke_preserve ()
| A drawing operator that strokes the current Path according to the current line width, line join, line cap, and dash settings. More...
void | fill ()
| A drawing operator that fills the current path according to the current fill rule, (each sub-path is implicitly closed before being filled). More...
void | fill_preserve ()
| A drawing operator that fills the current path according to the current fill rule, (each sub-path is implicitly closed before being filled). More...
void | copy_page ()
| Emits the current page for backends that support multiple pages, but doesn't clear it, so, the contents of the current page will be retained for the next page too. More...
void | show_page ()
| Emits and clears the current page for backends that support multiple pages. More...
bool | in_stroke (double x, double y) const
| Tests whether the given point is inside the area that would be affected by a stroke() operation given the current path and stroking parameters. More...
bool | in_fill (double x, double y) const
| Tests whether the given point is inside the area that would be affected by a fill() operation given the current path and filling parameters. More...
bool | in_clip (double x, double y) const
| Tests whether the given point is inside the area that would be visible through the current clip, i.e. More...
void | get_stroke_extents (double& x1, double& y1, double& x2, double& y2) const
| Computes a bounding box in user coordinates covering the area that would be affected, (the "inked" area), by a stroke() operation given the current path and stroke parameters. More...
void | get_fill_extents (double& x1, double& y1, double& x2, double& y2) const
| Computes a bounding box in user coordinates covering the area that would be affected, (the "inked" area), by a fill() operation given the current path and fill parameters. More...
void | reset_clip ()
| Reset the current clip region to its original, unrestricted state. More...
void | clip ()
| Establishes a new clip region by intersecting the current clip region with the current Path as it would be filled by fill() and according to the current fill rule. More...
void | clip_preserve ()
| Establishes a new clip region by intersecting the current clip region with the current path as it would be filled by fill() and according to the current fill rule. More...
void | get_clip_extents (double& x1, double& y1, double& x2, double& y2) const
| Computes a bounding box in user coordinates covering the area inside the current clip. More...
void | copy_clip_rectangle_list (std::vector< Rectangle >& rectangles) const
| Returns the current clip region as a list of rectangles in user coordinates. More...
void | select_font_face (const std::string& family, FontSlant slant, FontWeight weight)
| Selects a family and style of font from a simplified description as a family name, slant and weight. More...
void | set_font_size (double size)
| Sets the current font matrix to a scale by a factor of size, replacing any font matrix previously set with set_font_size() or set_font_matrix(). More...
void | set_font_matrix (const Matrix& matrix)
| Sets the current font matrix to . More...
void | get_font_matrix (Matrix& matrix) const
| Returns the current font matrix. More...
void | set_font_options (const FontOptions& options)
| Sets a set of custom font rendering options. More...
void | set_font_matrix (const cairo_matrix_t& matrix)
void | get_font_matrix (cairo_matrix_t& matrix) const
void | get_font_options (FontOptions& options) const
| Retrieves font rendering options set via set_font_options(). More...
void | set_scaled_font (const RefPtr< const ScaledFont >& scaled_font)
| Replaces the current font face, font matrix, and font options in the context with those of the scaled_font. More...
RefPtr< ScaledFont > | get_scaled_font ()
| Gets the current scaled font. More...
void | show_text (const std::string& utf8)
| A drawing operator that generates the shape from a string of UTF-8 characters, rendered according to the current font_face, font_size (font_matrix), and font_options. More...
void | show_glyphs (const std::vector< Glyph >& glyphs)
| A drawing operator that generates the shape from an array of glyphs, rendered according to the current font face, font size (font matrix), and font options. More...
void | show_text_glyphs (const std::string& utf8, const std::vector< Glyph >& glyphs, const std::vector< TextCluster >& clusters, TextClusterFlags cluster_flags)
| This operation has rendering effects similar to show_glyphs() but, if the target surface supports it, uses the provided text and cluster mapping to embed the text for the glyphs shown in the output. More...
void | get_font_extents (FontExtents& extents) const
| Gets the font extents for the currently selected font. More...
void | set_font_face (const RefPtr< const FontFace >& font_face)
| Replaces the current font face in the context with font_face font_face. More...
void | get_text_extents (const std::string& utf8, TextExtents& extents) const
| Gets the extents for a string of text. More...
void | get_glyph_extents (const std::vector< Glyph >& glyphs, TextExtents& extents) const
| Gets the extents for an array of glyphs. More...
void | text_path (const std::string& utf8)
| Adds closed paths for text to the current path. More...
void | glyph_path (const std::vector< Glyph >& glyphs)
| Adds closed paths for the glyphs to the current path. More...
Operator | get_operator () const
| Gets the current compositing operator for a cairo Context. More...
double | get_tolerance () const
| Gets the current tolerance value, as set by set_tolerance() More...
Antialias | get_antialias () const
| Gets the current shape antialiasing mode, as set by set_antialias() More...
void | get_current_point (double& x, double& y) const
| Gets the current point of the current path, which is conceptually the final point reached by the path so far. More...
bool | has_current_point () const
| Checks if there is a current point defined. More...
FillRule | get_fill_rule () const
| Gets the current fill rule, as set by set_fill_rule(). More...
double | get_line_width () const
| Gets the current line width, as set by set_line_width(). More...
LineCap | get_line_cap () const
| Gets the current line cap style, as set by set_line_cap() More...
LineJoin | get_line_join () const
| Gets the current line join style, as set by set_line_join() More...
double | get_miter_limit () const
| Gets the current miter limit, as set by set_miter_limit() More...
void | get_dash (std::vector< double >& dashes, double& offset) const
| Gets the current dash array and offset. More...
void | get_matrix (Matrix& matrix)
| Stores the current transformation matrix (CTM) into matrix. More...
void | get_matrix (cairo_matrix_t& matrix)
Matrix | get_matrix () const
| Returns the current transformation matrix (CTM) More...
Path* | copy_path () const
| Creates a copy of the current path and returns it to the user. More...
void | get_path_extents (double& x1, double& y1, double& x2, double& y2) const
| Computes a bounding box in user-space coordinates covering the points on the current path. More...
Path* | copy_path_flat () const
| Gets a flattened copy of the current path and returns it to the user. More...
void | append_path (const Path& path)
| Append the path onto the current path. More...
void | push_group ()
| Temporarily redirects drawing to an intermediate surface known as a group. More...
void | push_group_with_content (Content content)
| Temporarily redirects drawing to an intermediate surface known as a group. More...
RefPtr< Pattern > | pop_group ()
| Terminates the redirection begun by a call to push_group() or push_group_with_content() and returns a new pattern containing the results of all drawing operations performed to the group. More...
void | pop_group_to_source ()
| Terminates the redirection begun by a call to push_group() or push_group_with_content() and installs the resulting pattern as the source pattern in the given cairo Context. More...
RefPtr< Surface > | get_group_target ()
| Gets the target surface for the current group as started by the most recent call to push_group() or push_group_with_content(). More...
RefPtr< const Surface > | get_group_target () const
| Same as the non-const version but returns a reference to a const Surface. More...
cobject* | cobj ()
| Gets a pointer to the base C type that is wrapped by the Context. More...
const cobject* | cobj () const
| Gets a pointer to the base C type that is wrapped by the Context. More...
RefPtr< FontFace > | get_font_face ()
| Gets the current font face. More...
RefPtr< const FontFace > | get_font_face () const
RefPtr< Pattern > | get_source ()
| Gets the current source pattern for the Context. More...
RefPtr< const Pattern > | get_source () const
RefPtr< Surface > | get_target ()
| Gets the target surface associated with this Context. More...
RefPtr< const Surface > | get_target () const

## Static Public Member Functions

static RefPtr< Context > | create (const RefPtr< Surface >& target)

## Protected Member Functions

| Context (const RefPtr< Surface >& target)

## Protected Attributes

cobject* | m_cobject

## Detailed Description

Context is the main class used to draw in cairomm.

It contains the current state of the rendering device, including coordinates of yet to be drawn shapes.

In the simplest case, create a Context with its target Surface, set its drawing options (line width, color, etc), create shapes with methods like move_to() and line_to(), and then draw the shapes to the Surface using methods such as stroke() or fill().

Context is a reference-counted object that should be used via Cairo::RefPtr.

## Member Typedef Documentation

typedef cairo_t Cairo::Context::cobject

The base cairo C type that is wrapped by Cairo::Context.

## Constructor & Destructor Documentation

Cairo::Context::Context | ( | const RefPtr< Surface >& | target | ) |

explicit protected

Cairo::Context::Context | ( | cairo_t * | cobject,
|  | bool | has_reference = `false`
| ) |  |

explicit

Create a C++ wrapper for the C instance.

This C++ instance should then be given to a RefPtr.

Parameters

  cobject | The C instance.
  has_reference | Whether we already have a reference. Otherwise, the constructor will take an extra reference.

Cairo::Context::Context | ( | const Context& |  | ) |

delete

virtual Cairo::Context::~Context | ( |  | ) |

virtual

## Member Function Documentation

void Cairo::Context::append_path | ( | const Path& | path | ) |

Append the path onto the current path.

The path may be either the return value from one of copy_path() or copy_path_flat() or it may be constructed manually.

Parameters

  path | path to be appended

void Cairo::Context::arc | ( | double | xc,
|  | double | yc,
|  | double | radius,
|  | double | angle1,
|  | double | angle2
| ) |  |

Adds a circular arc of the given radius to the current path.

The arc is centered at (xc, yc), begins at angle1 and proceeds in the direction of increasing angles to end at angle2. If angle2 is less than angle1 it will be progressively increased by 2*M_PI until it is greater than angle1.

If there is a current point, an initial line segment will be added to the path to connect the current point to the beginning of the arc. If this initial line is undesired, it can be avoided by calling begin_new_sub_path() before calling arc().

Angles are measured in radians. An angle of 0 is in the direction of the positive X axis (in user-space). An angle of M_PI/2.0 radians (90 degrees) is in the direction of the positive Y axis (in user-space). Angles increase in the direction from the positive X axis toward the positive Y axis. So with the default transformation matrix, angles increase in a clockwise direction.

( To convert from degrees to radians, use degrees * (M_PI / 180.0). )

This function gives the arc in the direction of increasing angles; see arc_negative() to get the arc in the direction of decreasing angles.

The arc is circular in user-space. To achieve an elliptical arc, you can scale the current transformation matrix by different amounts in the X and Y directions. For example, to draw an ellipse in the box given by x, y, width, height:

context->save();
context->translate(x, y);
context->scale(width / 2.0, height / 2.0);
context->arc(0.0, 0.0, 1.0, 0.0, 2 * M_PI);
context->restore();

Parameters

  xc | X position of the center of the arc
  yc | Y position of the center of the arc
  radius | the radius of the arc
  angle1 | the start angle, in radians
  angle2 | the end angle, in radians

Examples:
  user-font.cc.

void Cairo::Context::arc_negative | ( | double | xc,
|  | double | yc,
|  | double | radius,
|  | double | angle1,
|  | double | angle2
| ) |  |

Adds a circular arc of the given radius to the current path.

The arc is centered at (xc, yc), begins at angle1 and proceeds in the direction of decreasing angles to end at angle2. If angle2 is greater than angle1 it will be progressively decreased by 2*M_PI until it is greater than angle1.

See arc() for more details. This function differs only in the direction of the arc between the two angles.

Parameters

  xc | X position of the center of the arc
  yc | Y position of the center of the arc
  radius | the radius of the arc
  angle1 | the start angle, in radians
  angle2 | the end angle, in radians

void Cairo::Context::begin_new_path | ( |  | ) |

Clears the current path.

After this call there will be no current point.

void Cairo::Context::begin_new_sub_path | ( |  | ) |

Begin a new subpath.

Note that the existing path is not affected. After this call there will be no current point.

In many cases, this call is not needed since new subpaths are frequently started with move_to().

A call to begin_new_sub_path() is particularly useful when beginning a new subpath with one of the arc() calls. This makes things easier as it is no longer necessary to manually compute the arc's initial coordinates for a call to move_to().

Since
  1.2

void Cairo::Context::clip | ( |  | ) |

Establishes a new clip region by intersecting the current clip region with the current Path as it would be filled by fill() and according to the current fill rule.

After clip(), the current path will be cleared from the cairo Context.

The current clip region affects all drawing operations by effectively masking out any changes to the surface that are outside the current clip region.

Calling clip() can only make the clip region smaller, never larger. But the current clip is part of the graphics state, so a temporary restriction of the clip region can be achieved by calling clip() within a save()/restore() pair. The only other means of increasing the size of the clip region is reset_clip().

See also
  set_fill_rule()

void Cairo::Context::clip_preserve | ( |  | ) |

Establishes a new clip region by intersecting the current clip region with the current path as it would be filled by fill() and according to the current fill rule.

Unlike clip(), clip_preserve preserves the path within the cairo Context.

See also
  clip()
  set_fill_rule()

void Cairo::Context::close_path | ( |  | ) |

Adds a line segment to the path from the current point to the beginning of the current subpath, (the most recent point passed to move_to()), and closes this subpath.

After this call the current point will be at the joined endpoint of the sub-path.

The behavior of close_path() is distinct from simply calling line_to() with the equivalent coordinate in the case of stroking. When a closed subpath is stroked, there are no caps on the ends of the subpath. Instead, there is a line join connecting the final and initial segments of the subpath.

If there is no current point before the call to close_path(), this function will have no effect.

cobject* Cairo::Context::cobj | ( |  | ) |

inline

Gets a pointer to the base C type that is wrapped by the Context.

const cobject* Cairo::Context::cobj | ( |  | ) | const

inline

Gets a pointer to the base C type that is wrapped by the Context.

void Cairo::Context::copy_clip_rectangle_list | ( | std::vector< Rectangle >& | rectangles | ) | const

Returns the current clip region as a list of rectangles in user coordinates.

This function will throw an exception if the clip region cannot be represented as a list of user-space rectangles.

Parameters

  rectangles | a vector to store the rectangles into

Exceptions

void Cairo::Context::copy_page | ( |  | ) |

Emits the current page for backends that support multiple pages, but doesn't clear it, so, the contents of the current page will be retained for the next page too.

Use show_page() if you want to get an empty page after the emission.

This is a convenience function that simply calls Surface::copy_page() on cr's target.

Path* Cairo::Context::copy_path | ( |  | ) | const

Creates a copy of the current path and returns it to the user.

Note
  The caller owns the Path object returned from this function. The Path object must be freed when you are finished with it.

Path* Cairo::Context::copy_path_flat | ( |  | ) | const

Gets a flattened copy of the current path and returns it to the user.

This function is like copy_path() except that any curves in the path will be approximated with piecewise-linear approximations, (accurate to within the current tolerance value). That is, the result is guaranteed to not have any elements of type CAIRO_PATH_CURVE_TO which will instead be replaced by a series of CAIRO_PATH_LINE_TO elements.

Note
  The caller owns the Path object returned from this function. The Path object must be freed when you are finished with it.

static RefPtr<Context> Cairo::Context::create | ( | const RefPtr< Surface >& | target | ) |

static

Examples:
  image-surface.cc, pdf-surface.cc, ps-surface.cc, svg-surface.cc, toy-text.cc, and user-font.cc.

void Cairo::Context::curve_to | ( | double | x1,
|  | double | y1,
|  | double | x2,
|  | double | y2,
|  | double | x3,
|  | double | y3
| ) |  |

Adds a cubic Bezier spline to the path from the current point to position (x3, y3) in user-space coordinates, using (x1, y1) and (x2, y2) as the control points.

After this call the current point will be (x3, y3).

If there is no current point before the call to curve_to() this function will behave as if preceded by a call to move_to(x1, y1).

Parameters

  x1 | the X coordinate of the first control point
  y1 | the Y coordinate of the first control point
  x2 | the X coordinate of the second control point
  y2 | the Y coordinate of the second control point
  x3 | the X coordinate of the end of the curve
  y3 | the Y coordinate of the end of the curve

void Cairo::Context::device_to_user | ( | double & | x,
|  | double & | y
| ) |  |

Transform a coordinate from device space to user space by multiplying the given point by the inverse of the current transformation matrix (CTM).

Parameters

  x | X value of coordinate (in/out parameter)
  y | Y value of coordinate (in/out parameter)

Deprecated:
  Use the const version.

void Cairo::Context::device_to_user | ( | double & | x,
|  | double & | y
| ) |  | const

Transform a coordinate from device space to user space by multiplying the given point by the inverse of the current transformation matrix (CTM).

Parameters

  x | X value of coordinate (in/out parameter)
  y | Y value of coordinate (in/out parameter)

void Cairo::Context::device_to_user_distance | ( | double & | dx,
|  | double & | dy
| ) |  |

Transform a distance vector from device space to user space.

This function is similar to device_to_user() except that the translation components of the inverse CTM will be ignored when transforming (dx,dy).

Parameters

  dx | X component of a distance vector (in/out parameter)
  dy | Y component of a distance vector (in/out parameter)

Deprecated:
  Use the const version.

void Cairo::Context::device_to_user_distance | ( | double & | dx,
|  | double & | dy
| ) |  | const

Transform a distance vector from device space to user space.

This function is similar to device_to_user() except that the translation components of the inverse CTM will be ignored when transforming (dx,dy).

Parameters

  dx | X component of a distance vector (in/out parameter)
  dy | Y component of a distance vector (in/out parameter)

void Cairo::Context::fill | ( |  | ) |

A drawing operator that fills the current path according to the current fill rule, (each sub-path is implicitly closed before being filled).

After fill(), the current path will be cleared from the cairo context.

See also
  set_fill_rule()
  fill_preserve()

Examples:
  user-font.cc.

void Cairo::Context::fill_preserve | ( |  | ) |

A drawing operator that fills the current path according to the current fill rule, (each sub-path is implicitly closed before being filled).

Unlike fill(), fill_preserve() preserves the path within the cairo Context.

See also
  set_fill_rule()
  fill().

Antialias Cairo::Context::get_antialias | ( |  | ) | const

Gets the current shape antialiasing mode, as set by set_antialias()

void Cairo::Context::get_clip_extents | ( | double & | x1,
|  | double & | y1,
|  | double & | x2,
|  | double & | y2
| ) |  | const

Computes a bounding box in user coordinates covering the area inside the current clip.

Parameters

  x1 | left of the resulting extents
  y1 | top of the resulting extents
  x2 | right of the resulting extents
  y2 | bottom of the resulting extents

Since
  1.4

void Cairo::Context::get_current_point | ( | double & | x,
|  | double & | y
| ) |  | const

Gets the current point of the current path, which is conceptually the final point reached by the path so far.

The current point is returned in the user-space coordinate system. If there is no defined current point then x and y will both be set to 0.0. It is possible to check this in advance with has_current_point().

Most path construction functions alter the current point. See the following for details on how they affect the current point: clear_path(), move_to(), line_to(), curve_to(), arc(), rel_move_to(), rel_line_to(), rel_curve_to(), arc(), and text_path()

Some functions use and alter the current point but do not otherwise change current path: show_text().

Some functions unset the current path and as a result, current point: fill(), stroke().

Parameters

  x | return value for X coordinate of the current point
  y | return value for Y coordinate of the current point

See also
  has_current_point()

void Cairo::Context::get_dash | ( | std::vector< double > & | dashes,
|  | double & | offset
| ) |  | const

Gets the current dash array and offset.

Parameters

  dashes | return value for the dash array.
  offset | return value for the current dash offset.

Since
  1.4

void Cairo::Context::get_fill_extents | ( | double & | x1,
|  | double & | y1,
|  | double & | x2,
|  | double & | y2
| ) |  | const

Computes a bounding box in user coordinates covering the area that would be affected, (the "inked" area), by a fill() operation given the current path and fill parameters.

If the current path is empty, returns an empty rectangle ((0,0), (0,0)). Surface dimensions and clipping are not taken into account.

Contrast with path_extents(), which is similar, but returns non-zero extents for some paths with no inked area, (such as a simple line segment).

Note that fill_extents() must necessarily do more work to compute the precise inked areas in light of the fill rule, so path_extents() may be more desirable for sake of performance if the non-inked path extents are desired.

Parameters

  x1 | left of the resulting extents
  y1 | top of the resulting extents
  x2 | right of the resulting extents
  y2 | bottom of the resulting extents

See also
  fill()
  set_fill_rule()
  full_preserve()

FillRule Cairo::Context::get_fill_rule | ( |  | ) | const

Gets the current fill rule, as set by set_fill_rule().

void Cairo::Context::get_font_extents | ( | FontExtents& | extents | ) | const

Gets the font extents for the currently selected font.

Parameters

  extents | a Cairo::FontExtents object

RefPtr<FontFace> Cairo::Context::get_font_face | ( |  | ) |

Gets the current font face.

RefPtr<const FontFace> Cairo::Context::get_font_face | ( |  | ) | const

void Cairo::Context::get_font_matrix | ( | Matrix& | matrix | ) | const

Returns the current font matrix.

Parameters

  matrix | a Cairo::Matrix to store the results into (in/out parameter)

See also
  set_font_matrix()

void Cairo::Context::get_font_matrix | ( | cairo_matrix_t& | matrix | ) | const

void Cairo::Context::get_font_options | ( | FontOptions& | options | ) | const

Retrieves font rendering options set via set_font_options().

Note that the returned options do not include any options derived from the underlying surface; they are literally the options passed to set_font_options().

Parameters

  options | a FontOptions object into which to store the retrieved options. All existing values are overwritten

Since
  1.8

void Cairo::Context::get_glyph_extents | ( | const std::vector< Glyph >& | glyphs,
|  | TextExtents& | extents
| ) |  | const

Gets the extents for an array of glyphs.

The extents describe a user-space rectangle that encloses the "inked" portion of the glyphs, (as they would be drawn by show_glyphs()). Additionally, the x_advance and y_advance values indicate the amount by which the current point would be advanced by show_glyphs().

Note that whitespace glyphs do not contribute to the size of the rectangle (extents.width and extents.height).

Parameters

  glyphs | a vector of glyphs
  extents | a TextExtents object

RefPtr<Surface> Cairo::Context::get_group_target | ( |  | ) |

Gets the target surface for the current group as started by the most recent call to push_group() or push_group_with_content().

This function will return NULL if called "outside" of any group rendering blocks, (that is, after the last balancing call to pop_group() or pop_group_to_source()).

Exceptions

RefPtr<const Surface> Cairo::Context::get_group_target | ( |  | ) | const

Same as the non-const version but returns a reference to a const Surface.

Since
  1.2

LineCap Cairo::Context::get_line_cap | ( |  | ) | const

Gets the current line cap style, as set by set_line_cap()

LineJoin Cairo::Context::get_line_join | ( |  | ) | const

Gets the current line join style, as set by set_line_join()

double Cairo::Context::get_line_width | ( |  | ) | const

Gets the current line width, as set by set_line_width().

Note that the value is unchanged even if the CTM has changed between the calls to set_line_width() and get_line_width().

void Cairo::Context::get_matrix | ( | Matrix& | matrix | ) |

Stores the current transformation matrix (CTM) into matrix.

Parameters

  matrix | return value for the matrix

void Cairo::Context::get_matrix | ( | cairo_matrix_t& | matrix | ) |

Matrix Cairo::Context::get_matrix | ( |  | ) | const

Returns the current transformation matrix (CTM)

Since
  1.8

double Cairo::Context::get_miter_limit | ( |  | ) | const

Gets the current miter limit, as set by set_miter_limit()

Operator Cairo::Context::get_operator | ( |  | ) | const

Gets the current compositing operator for a cairo Context.

void Cairo::Context::get_path_extents | ( | double & | x1,
|  | double & | y1,
|  | double & | x2,
|  | double & | y2
| ) |  | const

Computes a bounding box in user-space coordinates covering the points on the current path.

If the current path is empty, returns an empty rectangle ((0,0), (0,0)). Stroke parameters, fill rule, surface dimensions and clipping are not taken into account.

Contrast with fill_extents() and stroke_extents() which return the extents of only the area that would be "inked" by the corresponding drawing operations.

The result of path_extents() is defined as equivalent to the limit of stroke_extents() with LINE_CAP_ROUND as the line width approaches 0.0, (but never reaching the empty-rectangle returned by stroke_extents() for a line width of 0.0).

Specifically, this means that zero-area sub-paths such as move_to();line_to() segments, (even degenerate cases where the coordinates to both calls are identical), will be considered as contributing to the extents. However, a lone move_to() will not contribute to the results of path_extents().

Parameters

  x1 | left of the resulting extents
  y1 | top of the resulting extents
  x2 | right of the resulting extents
  y2 | bottom of the resulting extents

Since
  1.6

RefPtr<ScaledFont> Cairo::Context::get_scaled_font | ( |  | ) |

Gets the current scaled font.

Since
  1.8

RefPtr<Pattern> Cairo::Context::get_source | ( |  | ) |

Gets the current source pattern for the Context.

RefPtr<const Pattern> Cairo::Context::get_source | ( |  | ) | const

void Cairo::Context::get_stroke_extents | ( | double & | x1,
|  | double & | y1,
|  | double & | x2,
|  | double & | y2
| ) |  | const

Computes a bounding box in user coordinates covering the area that would be affected, (the "inked" area), by a stroke() operation given the current path and stroke parameters.

If the current path is empty, returns an empty rectangle ((0,0), (0,0)). Surface dimensions and clipping are not taken into account.

Note that if the line width is set to exactly zero, then stroke_extents() will return an empty rectangle. Contrast with path_extents() which can be used to compute the non-empty bounds as the line width approaches zero.

Note that stroke_extents() must necessarily do more work to compute the precise inked areas in light of the stroke parameters, so path_extents() may be more desirable for sake of performance if non-inked path extents are desired.

Parameters

  x1 | left of the resulting extents
  y1 | top of the resulting extents
  x2 | right of the resulting extents
  y2 | bottom of the resulting extents

See also
  stroke()
  set_line_width()
  set_line_join()
  set_line_cap()
  set_dash()
  stroke_preserve()

RefPtr<Surface> Cairo::Context::get_target | ( |  | ) |

Gets the target surface associated with this Context.

Exceptions

RefPtr<const Surface> Cairo::Context::get_target | ( |  | ) | const

void Cairo::Context::get_text_extents | ( | const std::string & | utf8,
|  | TextExtents& | extents
| ) |  | const

Gets the extents for a string of text.

The extents describe a user-space rectangle that encloses the "inked" portion of the text, (as it would be drawn by show_text()). Additionally, the x_advance and y_advance values indicate the amount by which the current point would be advanced by show_text().

Note that whitespace characters do not directly contribute to the size of the rectangle (extents.width and extents.height). They do contribute indirectly by changing the position of non-whitespace characters. In particular, trailing whitespace characters are likely to not affect the size of the rectangle, though they will affect the x_advance and y_advance values.

Parameters

  utf8 | a string of text encoded in UTF-8
  extents | a TextExtents object

double Cairo::Context::get_tolerance | ( |  | ) | const

Gets the current tolerance value, as set by set_tolerance()

void Cairo::Context::glyph_path | ( | const std::vector< Glyph >& | glyphs | ) |

Adds closed paths for the glyphs to the current path.

The generated path if filled, achieves an effect similar to that of show_glyphs().

Parameters

  glyphs | a vector of glyphs

bool Cairo::Context::has_current_point | ( |  | ) | const

Checks if there is a current point defined.

See get_current_point() for details on the current point.

Returns
  `true` if a current point is defined.

Since
  1.6

bool Cairo::Context::in_clip | ( | double | x,
|  | double | y
| ) |  | const

Tests whether the given point is inside the area that would be visible through the current clip, i.e.

the area that would be filled by a paint() operation.

Return value: A non-zero value if the point is inside, or zero if outside.

Parameters

  x | X coordinate of the point to test
  y | Y coordinate of the point to test

See also
  clip()
  clip_preserve()

Since
  1.10

bool Cairo::Context::in_fill | ( | double | x,
|  | double | y
| ) |  | const

Tests whether the given point is inside the area that would be affected by a fill() operation given the current path and filling parameters.

Surface dimensions and clipping are not taken into account.

Parameters

  x | X coordinate of the point to test
  y | Y coordinate of the point to test

Returns
  A non-zero value if the point is inside, or zero if outside.

See also
  fill()
  set_fill_rule()
  fill_preserve()

bool Cairo::Context::in_stroke | ( | double | x,
|  | double | y
| ) |  | const

Tests whether the given point is inside the area that would be affected by a stroke() operation given the current path and stroking parameters.

Surface dimensions and clipping are not taken into account.

Parameters

  x | X coordinate of the point to test
  y | Y coordinate of the point to test

Returns
  A non-zero value if the point is inside, or zero if outside.

See also
  stroke()
  set_line_width()
  set_line_join()
  set_line_cap()
  set_dash()
  stroke_preserve().

void Cairo::Context::line_to | ( | double | x,
|  | double | y
| ) |  |

Adds a line to the path from the current point to position (x, y) in user-space coordinates.

After this call the current point will be (x, y).

If there is no current point before the call to line_to() this function will behave as move_to(x, y).

Parameters

  x | the X coordinate of the end of the new line
  y | the Y coordinate of the end of the new line

void Cairo::Context::mask | ( | const RefPtr< const Pattern >& | pattern | ) |

A drawing operator that paints the current source using the alpha channel of pattern as a mask.

(Opaque areas of mask are painted with the source, transparent areas are not painted.)

Parameters

  pattern | a Pattern

void Cairo::Context::mask | ( | const RefPtr< const Surface >& | surface,
|  | double | surface_x,
|  | double | surface_y
| ) |  |

A drawing operator that paints the current source using the alpha channel of surface as a mask.

(Opaque areas of surface are painted with the source, transparent areas are not painted.)

Parameters

  surface | a Surface
  surface_x | X coordinate at which to place the origin of surface
  surface_y | Y coordinate at which to place the origin of surface

void Cairo::Context::move_to | ( | double | x,
|  | double | y
| ) |  |

If the current subpath is not empty, begin a new subpath.

After this call the current point will be (x, y).

Parameters

  x | the X coordinate of the new position
  y | the Y coordinate of the new position

Examples:
  user-font.cc.

Context& Cairo::Context::operator= | ( | const Context& |  | ) |

delete

void Cairo::Context::paint | ( |  | ) |

A drawing operator that paints the current source everywhere within the current clip region.

Examples:
  user-font.cc.

void Cairo::Context::paint_with_alpha | ( | double | alpha | ) |

A drawing operator that paints the current source everywhere within the current clip region using a mask of constant alpha value alpha.

The effect is similar to paint(), but the drawing is faded out using the alpha value.

Parameters

  alpha | an alpha value, between 0 (transparent) and 1 (opaque)

RefPtr<Pattern> Cairo::Context::pop_group | ( |  | ) |

Terminates the redirection begun by a call to push_group() or push_group_with_content() and returns a new pattern containing the results of all drawing operations performed to the group.

The pop_group() function calls restore(), (balancing a call to save() by the push_group function), so that any changes to the graphics state will not be visible outside the group.

Returns
  a (surface) pattern containing the results of all drawing operations performed to the group.

Since
  1.2

void Cairo::Context::pop_group_to_source | ( |  | ) |

Terminates the redirection begun by a call to push_group() or push_group_with_content() and installs the resulting pattern as the source pattern in the given cairo Context.

The behavior of this function is equivalent to the sequence of operations:

RefPtr<Pattern> group = cr->pop_group();
cr->set_source(group);

but is more convenient as their is no need for a variable to store the short-lived pointer to the pattern.

The pop_group() function calls restore(), (balancing a call to save() by the push_group function), so that any changes to the graphics state will not be visible outside the group.

Since
  1.2

void Cairo::Context::push_group | ( |  | ) |

Temporarily redirects drawing to an intermediate surface known as a group.

The redirection lasts until the group is completed by a call to pop_group() or pop_group_to_source(). These calls provide the result of any drawing to the group as a pattern, (either as an explicit object, or set as the source pattern).

This group functionality can be convenient for performing intermediate compositing. One common use of a group is to render objects as opaque within the group, (so that they occlude each other), and then blend the result with translucence onto the destination.

Groups can be nested arbitrarily deep by making balanced calls to push_group()/pop_group(). Each call pushes/pops the new target group onto/from a stack.

The push_group() function calls save() so that any changes to the graphics state will not be visible outside the group, (the pop_group functions call restore()).

By default the intermediate group will have a content type of CONTENT_COLOR_ALPHA. Other content types can be chosen for the group by using push_group_with_content() instead.

As an example, here is how one might fill and stroke a path with translucence, but without any portion of the fill being visible under the stroke:

cr->push_group();
cr->set_source(fill_pattern);
cr->fill_preserve();
cr->set_source(stroke_pattern);
cr->stroke();
cr->pop_group_to_source();
cr->paint_with_alpha(alpha);

Since
  1.2

void Cairo::Context::push_group_with_content | ( | Content | content | ) |

Temporarily redirects drawing to an intermediate surface known as a group.

The redirection lasts until the group is completed by a call to pop_group() or pop_group_to_source(). These calls provide the result of any drawing to the group as a pattern, (either as an explicit object, or set as the source pattern).

The group will have a content type of . The ability to control this content type is the only distinction between this function and push_group() which you should see for a more detailed description of group rendering.

Parameters

  content | indicates the type of group that will be created

Since
  1.2

void Cairo::Context::rectangle | ( | double | x,
|  | double | y,
|  | double | width,
|  | double | height
| ) |  |

Adds a closed-subpath rectangle of the given size to the current path at position (x, y) in user-space coordinates.

This function is logically equivalent to:

context->move_to(x, y);
context->rel_line_to(width, 0);
context->rel_line_to(0, height);
context->rel_line_to(-width, 0);
context->close_path();

Parameters

  x | the X coordinate of the top left corner of the rectangle
  y | the Y coordinate to the top left corner of the rectangle
  width | the width of the rectangle
  height | the height of the rectangle

Examples:
  user-font.cc.

void Cairo::Context::rel_curve_to | ( | double | dx1,
|  | double | dy1,
|  | double | dx2,
|  | double | dy2,
|  | double | dx3,
|  | double | dy3
| ) |  |

Relative-coordinate version of curve_to().

All offsets are relative to the current point. Adds a cubic Bezier spline to the path from the current point to a point offset from the current point by (dx3, dy3), using points offset by (dx1, dy1) and (dx2, dy2) as the control points. After this call the current point will be offset by (dx3, dy3).

Given a current point of (x, y),

rel_curve_to(dx1, dy1, dx2, dy2, dx3, dy3)

is logically equivalent to

curve_to(x + dx1, y + dy1, x + dx2, y + dy2, x + dx3, y + dy3).

Parameters

  dx1 | the X offset to the first control point
  dy1 | the Y offset to the first control point
  dx2 | the X offset to the second control point
  dy2 | the Y offset to the second control point
  dx3 | the X offset to the end of the curve
  dy3 | the Y offset to the end of the curve

It is an error to call this function with no current point. Doing so will cause this to shutdown with a status of CAIRO_STATUS_NO_CURRENT_POINT. Cairomm will then throw an exception.

void Cairo::Context::rel_line_to | ( | double | dx,
|  | double | dy
| ) |  |

Relative-coordinate version of line_to().

Adds a line to the path from the current point to a point that is offset from the current point by (dx, dy) in user space. After this call the current point will be offset by (dx, dy).

Given a current point of (x, y),

rel_line_to(dx, dy)

is logically equivalent to

line_to(x + dx, y + dy).

Parameters

  dx | the X offset to the end of the new line
  dy | the Y offset to the end of the new line

It is an error to call this function with no current point. Doing so will cause this to shutdown with a status of CAIRO_STATUS_NO_CURRENT_POINT. Cairomm will then throw an exception.

void Cairo::Context::rel_move_to | ( | double | dx,
|  | double | dy
| ) |  |

If the current subpath is not empty, begin a new subpath.

After this call the current point will offset by (x, y).

Given a current point of (x, y),

rel_move_to(dx, dy)

is logically equivalent to

move_to(x + dx, y + dy)

Parameters

  dx | the X offset
  dy | the Y offset

It is an error to call this function with no current point. Doing so will cause this to shutdown with a status of CAIRO_STATUS_NO_CURRENT_POINT. Cairomm will then throw an exception.

void Cairo::Context::reset_clip | ( |  | ) |

Reset the current clip region to its original, unrestricted state.

That is, set the clip region to an infinitely large shape containing the target surface. Equivalently, if infinity is too hard to grasp, one can imagine the clip region being reset to the exact bounds of the target surface.

Note that code meant to be reusable should not call reset_clip() as it will cause results unexpected by higher-level code which calls clip(). Consider using save() and restore() around clip() as a more robust means of temporarily restricting the clip region.

void Cairo::Context::restore | ( |  | ) |

Restores cr to the state saved by a preceding call to save() and removes that state from the stack of saved states.

See also
  save()

void Cairo::Context::rotate | ( | double | angle_radians | ) |

Modifies the current transformation matrix (CTM) by rotating the user-space axes by angle radians.

The rotation of the axes takes places after any existing transformation of user space. The rotation direction for positive angles is from the positive X axis toward the positive Y axis.

Parameters

  angle | angle (in radians) by which the user-space axes will be rotated

void Cairo::Context::rotate_degrees | ( | double | angle_degres | ) |

A convenience wrapper around rotate() that accepts angles in degrees.

Parameters

  angle_degrees | angle (in degrees) by which the user-space axes should be rotated

void Cairo::Context::save | ( |  | ) |

Makes a copy of the current state of the Context and saves it on an internal stack of saved states.

When restore() is called, it will be restored to the saved state. Multiple calls to save() and restore() can be nested; each call to restore() restores the state from the matching paired save().

It isn't necessary to clear all saved states before a cairo_t is freed. Any saved states will be freed when the Context is destroyed.

See also
  restore()

void Cairo::Context::scale | ( | double | sx,
|  | double | sy
| ) |  |

Modifies the current transformation matrix (CTM) by scaling the X and Y user-space axes by sx and sy respectively.

The scaling of the axes takes place after any existing transformation of user space.

Parameters

  sx | scale factor for the X dimension
  sy | scale factor for the Y dimension

void Cairo::Context::select_font_face | ( | const std::string & | family,
|  | FontSlant | slant,
|  | FontWeight | weight
| ) |  |

Selects a family and style of font from a simplified description as a family name, slant and weight.

Cairo provides no operation to list available family names on the system (this is a "toy", remember), but the standard CSS2 generic family names, ("serif", "sans-serif", "cursive", "fantasy", "monospace"), are likely to work as expected.

Note: The select_font_face() function call is part of what the cairo designers call the "toy" text API. It is convenient for short demos and simple programs, but it is not expected to be adequate for serious text-using applications.

If family starts with the string "@cairo:", or if no native font backends are compiled in, cairo will use an internal font family. The internal font family recognizes many modifiers in the string, most notably, it recognizes the string "monospace". That is, the family name "@cairo:monospace" will use the monospace version of the internal font family.

For "real" font selection, see the font-backend-specific Cairo::FontFace::create functions for the font backend you are using. (For example, if you are using the freetype-based cairo-ft font backend, see Cairo::FtFontFace::create().) The resulting font face could then be used with Cairo::ScaledFont::create() and set_scaled_font().

Similarly, when using the "real" font support, you can call directly into the underlying font system, (such as fontconfig or freetype), for operations such as listing available fonts, etc.

It is expected that most applications will need to use a more comprehensive font handling and text layout library, (for example, pango), in conjunction with cairo.

If text is drawn without a call to select_font_face(), (nor set_font_face() nor set_scaled_font()), the default family is platform-specific, but is essentially "sans-serif". Default slant is Cairo::FONT_SLANT_NORMAL, and default weight is Cairo::FONT_WEIGHT_NORMAL.

This function is equivalent to a call to Cairo::ToyFontFace::create() followed by set_font_face().

Parameters

  family | a font family name, encoded in UTF-8
  slant | the slant for the font
  weight | the weight for the font

void Cairo::Context::set_antialias | ( | Antialias | antialias | ) |

Set the antialiasing mode of the rasterizer used for drawing shapes.

This value is a hint, and a particular backend may or may not support a particular value. At the current time, no backend supports Cairo::ANTIALIAS_SUBPIXEL when drawing shapes.

Note that this option does not affect text rendering, instead see FontOptions::set_antialias().

Parameters

  antialias | the new antialiasing mode

void Cairo::Context::set_dash | ( | std::valarray< double > & | dashes,
|  | double | offset
| ) |  |

Alternate version of set_dash().

You'll probably want to use the one that takes a std::vector argument instead.

Deprecated:
  Instead use the version that takes a const dashes parameter.

void Cairo::Context::set_dash | ( | std::vector< double > & | dashes,
|  | double | offset
| ) |  |

Sets the dash pattern to be used by stroke().

A dash pattern is specified by dashes, an array of positive values. Each value provides the user-space length of altenate "on" and "off" portions of the stroke. The offset specifies an offset into the pattern at which the stroke begins.

If dashes is empty dashing is disabled. If the size of dashes is 1, a symmetric pattern is assumed with alternating on and off portions of the size specified by the single value in dashes.

It is invalid for any value in dashes to be negative, or for all values to be 0. If this is the case, an exception will be thrown

Parameters

  dashes | an array specifying alternate lengths of on and off portions
  offset | an offset into the dash pattern at which the stroke should start

Exceptions

void Cairo::Context::set_dash | ( | const std::valarray< double > & | dashes,
|  | double | offset
| ) |  |

Alternate version of set_dash().

You'll probably want to use the one that takes a std::vector argument instead.

void Cairo::Context::set_dash | ( | const std::vector< double > & | dashes,
|  | double | offset
| ) |  |

Sets the dash pattern to be used by stroke().

A dash pattern is specified by dashes, an array of positive values. Each value provides the user-space length of altenate "on" and "off" portions of the stroke. The offset specifies an offset into the pattern at which the stroke begins.

Each "on" segment will have caps applied as if the segment were a separate sub-path. In particular, it is valid to use an "on" length of 0.0 with Cairo::LINE_CAP_ROUND or Cairo::LINE_CAP_SQUARE in order to distributed dots or squares along a path.

Note: The length values are in user-space units as evaluated at the time of stroking. This is not necessarily the same as the user space at the time of set_dash().

If dashes is empty dashing is disabled. If the size of dashes is 1, a symmetric pattern is assumed with alternating on and off portions of the size specified by the single value in dashes.

It is invalid for any value in dashes to be negative, or for all values to be 0. If this is the case, an exception will be thrown

Parameters

  dashes | an array specifying alternate lengths of on and off portions
  offset | an offset into the dash pattern at which the stroke should start

Exceptions

void Cairo::Context::set_fill_rule | ( | FillRule | fill_rule | ) |

Set the current fill rule within the cairo Context.

The fill rule is used to determine which regions are inside or outside a complex (potentially self-intersecting) path. The current fill rule affects both fill() and clip(). See FillRule for details on the semantics of each available fill rule.

The default fill rule is Cairo::FILL_RULE_WINDING.

Parameters

  fill_rule | a fill rule, specified as a FillRule

void Cairo::Context::set_font_face | ( | const RefPtr< const FontFace >& | font_face | ) |

Replaces the current font face in the context with font_face font_face.

The replaced font face in the context will be destroyed if there are no other references to it.

Parameters

  font_face | a font face

Examples:
  user-font.cc.

void Cairo::Context::set_font_matrix | ( | const Matrix& | matrix | ) |

Sets the current font matrix to .

The font matrix gives a transformation from the design space of the font (in this space, the em-square is 1 unit by 1 unit) to user space. Normally, a simple scale is used (see set_font_size()), but a more complex font matrix can be used to shear the font or stretch it unequally along the two axes

Parameters

  matrix | a Cairo::Matrix describing a transform to be applied to the current font.

void Cairo::Context::set_font_matrix | ( | const cairo_matrix_t& | matrix | ) |

void Cairo::Context::set_font_options | ( | const FontOptions& | options | ) |

Sets a set of custom font rendering options.

Rendering options are derived by merging these options with the options derived from underlying surface; if the value in options has a default value (like Cairo::ANTIALIAS_DEFAULT), then the value from the surface is used.

Parameters

  options | font options to use

void Cairo::Context::set_font_size | ( | double | size | ) |

Sets the current font matrix to a scale by a factor of size, replacing any font matrix previously set with set_font_size() or set_font_matrix().

This results in a font size of size user space units. (More precisely, this matrix will result in the font's em-square being a by size square in user space.)

If text is drawn without a call to set_font_size(), (nor set_font_matrix() nor set_scaled_font()), the default font size is 10.0.

Parameters

  size | the new font size, in user space units)

Examples:
  user-font.cc.

void Cairo::Context::set_identity_matrix | ( |  | ) |

Resets the current transformation matrix (CTM) by setting it equal to the identity matrix.

That is, the user-space and device-space axes will be aligned and one user-space unit will transform to one device-space unit.

void Cairo::Context::set_line_cap | ( | LineCap | line_cap | ) |

Sets the current line cap style within the cairo Context.

See LineCap for details about how the available line cap styles are drawn.

As with the other stroke parameters, the current line cap style is examined by stroke(), stroke_extents(), and stroke_to_path(), but does not have any effect during path construction.

The default line cap style is Cairo::LINE_CAP_BUTT.

Parameters

  line_cap | a line cap style, as a LineCap

void Cairo::Context::set_line_join | ( | LineJoin | line_join | ) |

Sets the current line join style within the cairo Context.

See LineJoin for details about how the available line join styles are drawn.

As with the other stroke parameters, the current line join style is examined by stroke(), stroke_extents(), and stroke_to_path(), but does not have any effect during path construction.

The default line join style is Cairo::LINE_JOIN_MITER.

Parameters

  line_join | a line joint style, as a LineJoin

void Cairo::Context::set_line_width | ( | double | width | ) |

Sets the current line width within the cairo Context.

The line width specifies the diameter of a pen that is circular in user-space, (though device-space pen may be an ellipse in general due to scaling/shear/rotation of the CTM).

Note: When the description above refers to user space and CTM it refers to the user space and CTM in effect at the time of the stroking operation, not the user space and CTM in effect at the time of the call to set_line_width(). The simplest usage makes both of these spaces identical. That is, if there is no change to the CTM between a call to set_line_width() and the stroking operation, then one can just pass user-space values to set_line_width() and ignore this note.

As with the other stroke parameters, the current line cap style is examined by stroke(), stroke_extents(), and stroke_to_path(), but does not have any effect during path construction.

The default line width value is 2.0.

Parameters

  width | a line width, as a user-space value

Examples:
  user-font.cc.

void Cairo::Context::set_matrix | ( | const Matrix& | matrix | ) |

Modifies the current transformation matrix (CTM) by setting it equal to matrix.

Parameters

  matrix | a transformation matrix from user space to device space

void Cairo::Context::set_matrix | ( | const cairo_matrix_t& | matrix | ) |

void Cairo::Context::set_miter_limit | ( | double | limit | ) |

Sets the current miter limit within the cairo context.

If the current line join style is set to Cairo::LINE_JOIN_MITER (see set_line_join()), the miter limit is used to determine whether the lines should be joined with a bevel instead of a miter. Cairo divides the length of the miter by the line width. If the result is greater than the miter limit, the style is converted to a bevel.

As with the other stroke parameters, the current line miter limit is examined by stroke(), stroke_extents(), and stroke_to_path(), but does not have any effect during path construction.

The default miter limit value is 10.0, which will convert joins with interior angles less than 11 degrees to bevels instead of miters. For reference, a miter limit of 2.0 makes the miter cutoff at 60 degrees, and a miter limit of 1.414 makes the cutoff at 90 degrees.

A miter limit for a desired angle can be computed as: miter_limit = 1/sin(angle/2)

Parameters

  limit | miter limit to set

void Cairo::Context::set_operator | ( | Operator | op | ) |

Sets the compositing operator to be used for all drawing operations.

See Operator for details on the semantics of each available compositing operator.

Parameters

  op | a compositing operator, specified as a Operator

void Cairo::Context::set_scaled_font | ( | const RefPtr< const ScaledFont >& | scaled_font | ) |

Replaces the current font face, font matrix, and font options in the context with those of the scaled_font.

Except for some translation, the current CTM of the context should be the same as that of the #cairo_scaled_font_t, which can be accessed using Cairo::ScaledFont::get_ctm().

Parameters

  scaled_font | a scaled font

Since
  1.8

void Cairo::Context::set_source | ( | const RefPtr< const Pattern >& | source | ) |

Sets the source pattern within the Context to source.

This Pattern will then be used for any subsequent drawing operation until a new source pattern is set.

Note: The Pattern's transformation matrix will be locked to the user space in effect at the time of set_source(). This means that further modifications of the current transformation matrix will not affect the source pattern.

Parameters

  source | a Pattern to be used as the source for subsequent drawing operations.

See also
  Pattern::set_matrix()
  set_source_rgb()
  set_source_rgba()
  set_source(const RefPtr<Surface>& surface, double x, double y)

void Cairo::Context::set_source | ( | const RefPtr< Surface >& | surface,
|  | double | x,
|  | double | y
| ) |  |

This is a convenience function for creating a pattern from a Surface and setting it as the source.

The x and y parameters give the user-space coordinate at which the Surface origin should appear. (The Surface origin is its upper-left corner before any transformation has been applied.) The x and y patterns are negated and then set as translation values in the pattern matrix.

Other than the initial translation pattern matrix, as described above, all other pattern attributes, (such as its extend mode), are set to the default values as in Context::create(const RefPtr<Surface>& target). The resulting pattern can be queried with get_source() so that these attributes can be modified if desired, (eg. to create a repeating pattern with Pattern::set_extend()).

Parameters

  surface | a Surface to be used to set the source pattern
  x | User-space X coordinate for surface origin
  y | User-space Y coordinate for surface origin

void Cairo::Context::set_source_rgb | ( | double | red,
|  | double | green,
|  | double | blue
| ) |  |

Sets the source pattern within the Context to an opaque color.

This opaque color will then be used for any subsequent drawing operation until a new source pattern is set.

The color components are floating point numbers in the range 0 to 1. If the values passed in are outside that range, they will be clamped.

Parameters

  red | red component of color
  green | green component of color
  blue | blue component of color

See also
  set_source_rgba()
  set_source()

Examples:
  user-font.cc.

void Cairo::Context::set_source_rgba | ( | double | red,
|  | double | green,
|  | double | blue,
|  | double | alpha
| ) |  |

Sets the source pattern within the Context to a translucent color.

This color will then be used for any subsequent drawing operation until a new source pattern is set.

The color and alpha components are floating point numbers in the range 0 to 1. If the values passed in are outside that range, they will be clamped.

Parameters

  red | red component of color
  green | green component of color
  blue | blue component of color
  alpha | alpha component of color

See also
  set_source_rgb()
  set_source()

Examples:
  user-font.cc.

void Cairo::Context::set_tolerance | ( | double | tolerance | ) |

Sets the tolerance used when converting paths into trapezoids.

Curved segments of the path will be subdivided until the maximum deviation between the original path and the polygonal approximation is less than tolerance. The default value is 0.1. A larger value will give better performance, a smaller value, better appearance. (Reducing the value from the default value of 0.1 is unlikely to improve appearance significantly.) The accuracy of paths within Cairo is limited by the precision of its internal arithmetic, and the prescribed is restricted to the smallest representable internal value.

Parameters

  tolerance | the tolerance, in device units (typically pixels)

void Cairo::Context::show_glyphs | ( | const std::vector< Glyph >& | glyphs | ) |

A drawing operator that generates the shape from an array of glyphs, rendered according to the current font face, font size (font matrix), and font options.

Parameters

  glyphs | vector of glyphs to show
  num_glyphs | number of glyphs to show

void Cairo::Context::show_page | ( |  | ) |

Emits and clears the current page for backends that support multiple pages.

Use copy_page() if you don't want to clear the page.

This is a convenience function that simply calls Surface::show_page() on cr's target.

void Cairo::Context::show_text | ( | const std::string & | utf8 | ) |

A drawing operator that generates the shape from a string of UTF-8 characters, rendered according to the current font_face, font_size (font_matrix), and font_options.

This function first computes a set of glyphs for the string of text. The first glyph is placed so that its origin is at the current point. The origin of each subsequent glyph is offset from that of the previous glyph by the advance values of the previous glyph.

After this call the current point is moved to the origin of where the next glyph would be placed in this same progression. That is, the current point will be at the origin of the final glyph offset by its advance values. This allows for easy display of a single logical string with multiple calls to show_text().

Note: The show_text() function call is part of what the cairo designers call the "toy" text API. It is convenient for short demos and simple programs, but it is not expected to be adequate for serious text-using applications. See show_glyphs() for the "real" text display API in cairo.

Parameters

  utf8 | a string containing text encoded in UTF-8

Examples:
  user-font.cc.

void Cairo::Context::show_text_glyphs | ( | const std::string & | utf8,
|  | const std::vector< Glyph >& | glyphs,
|  | const std::vector< TextCluster >& | clusters,
|  | TextClusterFlags | cluster_flags
| ) |  |

This operation has rendering effects similar to show_glyphs() but, if the target surface supports it, uses the provided text and cluster mapping to embed the text for the glyphs shown in the output.

If the target does not support the extended attributes, this function acts like the basic show_glyphs() as if it had been passed glyphs and num_glyphs.

The mapping between utf8 and glyphs is provided by an array of <firstterm>clusters</firstterm>. Each cluster covers a number of text bytes and glyphs, and neighboring clusters cover neighboring areas of utf8 and glyphs. The clusters should collectively cover utf8 and glyphs in entirety.

The first cluster always covers bytes from the beginning of utf8. If cluster_flags do not have the Cairo::TEXT_CLUSTER_FLAG_BACKWARD set, the first cluster also covers the beginning of glyphs, otherwise it covers the end of the glyphs array and following clusters move backward.

See Cairo::TextCluster for constraints on valid clusters.

Parameters

  utf8 | a string of text encoded in UTF-8
  glyphs | vector of glyphs to show
  clusters | vector of cluster mapping information
  cluster_flags | cluster mapping flags

Since
  1.8

void Cairo::Context::stroke | ( |  | ) |

A drawing operator that strokes the current Path according to the current line width, line join, line cap, and dash settings.

After stroke(), the current Path will be cleared from the cairo Context.

See also
  set_line_width()
  set_line_join()
  set_line_cap()
  set_dash()
  stroke_preserve().

Note: Degenerate segments and sub-paths are treated specially and provide a useful result. These can result in two different situations:

1. Zero-length "on" segments set in set_dash(). If the cap style is Cairo::LINE_CAP_ROUND or Cairo::LINE_CAP_SQUARE then these segments will be drawn as circular dots or squares respectively. In the case of Cairo::LINE_CAP_SQUARE, the orientation of the squares is determined by the direction of the underlying path.
2. A sub-path created by move_to() followed by either a close_path() or one or more calls to line_to() to the same coordinate as the move_to(). If the cap style is Cairo::LINE_CAP_ROUND then these sub-paths will be drawn as circular dots. Note that in the case of Cairo::LINE_CAP_SQUARE a degenerate sub-path will not be drawn at all, (since the correct orientation is indeterminate).

In no case will a cap style of Cairo::LINE_CAP_BUTT cause anything to be drawn in the case of either degenerate segments or sub-paths.

Examples:
  user-font.cc.

void Cairo::Context::stroke_preserve | ( |  | ) |

A drawing operator that strokes the current Path according to the current line width, line join, line cap, and dash settings.

Unlike stroke(), stroke_preserve() preserves the Path within the cairo Context.

See also
  set_line_width()
  set_line_join()
  set_line_cap()
  set_dash()
  stroke_preserve().

void Cairo::Context::text_path | ( | const std::string & | utf8 | ) |

Adds closed paths for text to the current path.

The generated path if filled, achieves an effect similar to that of show_text().

Text conversion and positioning is done similar to show_text().

Like show_text(), After this call the current point is moved to the origin of where the next glyph would be placed in this same progression. That is, the current point will be at the origin of the final glyph offset by its advance values. This allows for chaining multiple calls to to text_path() without having to set current point in between.

Note: The text_path() function call is part of what the cairo designers call the "toy" text API. It is convenient for short demos and simple programs, but it is not expected to be adequate for serious text-using applications. See glyph_path() for the "real" text path API in cairo.

Parameters

  utf8 | a string of text encoded in UTF-8

void Cairo::Context::transform | ( | const Matrix& | matrix | ) |

Modifies the current transformation matrix (CTM) by applying matrix as an additional transformation.

The new transformation of user space takes place after any existing transformation.

Parameters

  matrix | a transformation to be applied to the user-space axes

void Cairo::Context::transform | ( | const cairo_matrix_t& | matrix | ) |

void Cairo::Context::translate | ( | double | tx,
|  | double | ty
| ) |  |

Modifies the current transformation matrix (CTM) by translating the user-space origin by (tx, ty).

This offset is interpreted as a user-space coordinate according to the CTM in place before the new call to translate. In other words, the translation of the user-space origin takes place after any existing transformation.

Parameters

  tx | amount to translate in the X direction
  ty | amount to translate in the Y direction

void Cairo::Context::unset_dash | ( |  | ) |

This function disables a dash pattern that was set with set_dash()

void Cairo::Context::user_to_device | ( | double & | x,
|  | double & | y
| ) |  |

Transform a coordinate from user space to device space by multiplying the given point by the current transformation matrix (CTM).

Parameters

  x | X value of coordinate (in/out parameter)
  y | Y value of coordinate (in/out parameter)

Deprecated:
  Use the const version.

void Cairo::Context::user_to_device | ( | double & | x,
|  | double & | y
| ) |  | const

Transform a coordinate from user space to device space by multiplying the given point by the current transformation matrix (CTM).

Parameters

  x | X value of coordinate (in/out parameter)
  y | Y value of coordinate (in/out parameter)

void Cairo::Context::user_to_device_distance | ( | double & | dx,
|  | double & | dy
| ) |  |

Transform a distance vector from user space to device space.

This function is similar to user_to_device() except that the translation components of the CTM will be ignored when transforming (dx,dy).

Parameters

  dx | X component of a distance vector (in/out parameter)
  dy | Y component of a distance vector (in/out parameter)

Deprecated:
  Use the const version.

void Cairo::Context::user_to_device_distance | ( | double & | dx,
|  | double & | dy
| ) |  | const

Transform a distance vector from user space to device space.

This function is similar to user_to_device() except that the translation components of the CTM will be ignored when transforming (dx,dy).

Parameters

  dx | X component of a distance vector (in/out parameter)
  dy | Y component of a distance vector (in/out parameter)

## Member Data Documentation

cobject* Cairo::Context::m_cobject

protected

The documentation for this class was generated from the following file:

- cairomm/context.h