Gnome::Cairo

The cairo drawing context

Description

cairo_t is the main object used when drawing with cairo. To draw with cairo, you create a cairo_t, set the target surface, and drawing options for the cairo_t, create shapes with functions like move_to() and line_to(), and then draw shapes with stroke() or fill(). cairo_t ‘s can be pushed to a stack via save(). They may then safely be changed, without losing the current state. Use restore() to restore to the saved state.

Synopsis

Declaration

unit class Gnome::Cairo;
also is Gnome::N::TopLevelClassSupport;

Methods

new

:surface

Creates a new cairo_t with all graphics state parameters set to default values and with target as a target surface. The target surface should be constructed with a backend-specific function such as Gnome::Cairo::ImageSurface.new(…).

This function references $surface, so you can immediately call clear-object() on it if you don’t need to maintain a separate reference to it.

The object is cleared with clear-object() when you are done using the cairo_t. This function never returns Any. If memory cannot be allocated, a special cairo_t object will be returned on which status() returns CAIRO_STATUS_NO_MEMORY. If you attempt to target a surface which does not support writing (such as cairo_mime_surface_t) then a CAIRO_STATUS_WRITE_ERROR will be raised.

You can use this object normally, but no drawing will be done.

multi method new ( cairo_surface_t :$surface! )

cairo_surface_t $surface;

:native-object

Create a Gnome::Cairo object using a native object from elsewhere. See also Gnome::N::TopLevelClassSupport.

multi method new ( N-GObject :$native-object! )

append-path

Append the $path onto the current path. Note that Gnome::Cairo::Path.status() must be CAIRO_STATUS_SUCCESS.

method append-path ( cairo_path_t $path )

$path; path to be appended

arc

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*π 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 new-sub-path() before calling arc().

Angles are measured in radians. An angle of 0.0 is in the direction of the positive X axis (in user space). An angle of π/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 * (π / 180).) 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:

  with $cairo {
    .save;
    .translate( $x + $width / 2, $y + $height / 2);
    .scale( $width / 2, $height / 2);
    .arc( 0, 0, 1, 0, 2 * π);
    .restore;
  }

  method arc (
    Num() $xc, Num() $yc, Num() $radius, Num() $angle1, Num() $angle2
  )

$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

arc-negative

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 * π until it is less than $angle1. See arc() for more details. This function differs only in the direction of the arc between the two angles.

method arc-negative (
  Num() $xc, Num() $yc, Num() $radius, Num() $angle1, Num() $angle2
)

$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

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 (see set-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().

method clip ( )

clip-extents

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

method clip-extents ( --> List )

List holds the following values

Num $x1; left of the resulting extents
Num $y1; top of the resulting extents
Num $x2; right of the resulting extents
Num $y2; bottom of the resulting extents

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 (see set-fill-rule()).

Unlike clip(), clip-preserve() preserves the path within 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-preserve() 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 preserve() within a save()/restore() pair. The only other means of increasing the size of the clip region is reset-clip().

method clip-preserve ( )

close-path

Adds a line segment to the path from the current point to the beginning of the current sub-path, (the most recent point passed to move-to()), and closes this sub-path. 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 sub-path is stroked, there are no caps on the ends of the sub-path. Instead, there is a line join connecting the final and initial segments of the sub-path.

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

Note: As of cairo version 1.2.4 any call to close-path() will place an explicit MOVE_TO element into the path immediately after the CLOSE_PATH element, (which can be seen in copy-path() for example). This can simplify path processing in some cases as it may not be necessary to save the “last move_to point” during processing as the MOVE_TO immediately after the CLOSE_PATH will provide that point.

method close-path ( )

copy-clip-rectangle-list

Gets the current clip region as a list of rectangles in user coordinates. Never returns an undefined list.

The status in the list may be CAIRO_STATUS_CLIP_NOT_REPRESENTABLE to indicate that the clip region cannot be represented as a list of user-space rectangles. The status may have other values to indicate other errors.

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

method copy-clip-rectangle-list ( --> cairo_rectangle_list_t )

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 Gnome::Cairo::Surface.copy-page() on this context’s target.

method copy-page ( )

copy-path

Creates a copy of the current path and returns it to the user as a cairo_path_t. See cairo_path_data_t for hints on how to iterate over the returned data structure.

This function will always return a valid pointer, but the result will have no data, if either of the following conditions hold:

If there is insufficient memory to copy the path. In this case $path.status will be set to CAIRO_STATUS_NO_MEMORY.
If the context is already in an error state. In this case $path.status will contain the same status that would be returned by .status().

Return value: the copy of the current path. The caller owns the returned object and should call clear-object() when finished with it.

method copy-path ( --> cairo_path_t )

copy-path-flat

Gets a flattened copy of the current path and returns it to the user as a cairo_path_t. See cairo_path_data_t for hints on how to iterate over the returned data structure. 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.

This function will always return a valid pointer, but the result will have no data, if either of the following conditions hold:

If there is insufficient memory to copy the path. In this case $path.status will be set to CAIRO_STATUS_NO_MEMORY.
If the context is already in an error state. In this case $path.status will contain the same status that would be returned by .status().

Return value: the copy of the current path. The caller owns the returned object and should call clear-object() when finished with it.

method copy-path-flat ( --> cairo_path_t )

curve-to

Adds a cubic Bézier 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 cairo_move_to(this context, x1, y1).

method curve-to ( Num() $x1, Num() $y1, Num() $x2, Num() $y2, Num() $x3, Num() $y3 )

$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

device-to-user

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

method device-to-user ( Num() $x is rw, Num() $y is rw )

$x; X value of coordinate
$y; Y value of coordinate

device-to-user-distance

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).

method device-to-user-distance ( Num() $dx is rw, Num() $dy is rw )

$dx; y component of a distance vector
$dy; X component of a distance vector

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 set-fill-rule() and fill-preserve().

method fill ( )

fill-extents

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.

See fill(), set-fill-rule() and fill-preserve().

method fill-extents ( --> List )

List returns

Num; left of the resulting extents
Num; top of the resulting extents
Num; right of the resulting extents
Num; bottom of the resulting extents

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 set-fill-rule() and fill().

method fill-preserve ( )

get-antialias

Gets the current shape antialiasing mode, as set by set-antialias(). Return value: the current shape antialiasing mode.

method get-antialias ( --> cairo_antialias_t )

get-current-point

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 or if this object is not valid, $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: new-path(), new-sub-path(), append-path(), close-path(), move-to(), line-to(), curve-to(), rel-move-to(), rel-line-to(), rel-curve-to(), arc(), arc-negative(), rectangle(), text-path(), glyph-path(), stroke-to-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().

method get-current-point ( --> List )

The returned list has;

$x; X coordinate of the current point
$y; Y coordinate of the current point

get-dash

Gets the current dash array.

method get-dash ( --> List )

List returns;

Array; the dash array
Num; the current dash offset, or Undefined

get-dash-count

This function returns the length of the dash array in this context (0 if dashing is not currently in effect). See also set-dash() and get-dash(). Return value: the length of the dash array, or 0 if no dash array set.

method get-dash-count ( --> Int )

get-fill-rule

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

Return value: the current fill rule.

method get-fill-rule ( --> cairo_fill_rule_t )

get-font-face

Gets the current font face for a cairo_t.

Return value: the current font face.

This function never returns an undefined font face. If memory cannot be allocated, a special “nil” cairo_font_face_t object will be returned on which Gnome::Cairo::FontFace.status() returns CAIRO_STATUS_NO_MEMORY. Using this nil object will cause its error state to propagate to other objects it is passed to, (for example, calling set-font-face() with a nil font will trigger an error that will shutdown the cairo_t object).

method get-font-face ( --> Gnome::Cairo::FontFace )

get-font-matrix

Returns the current font matrix. See set-font-matrix().

method get-font-matrix ( --> Gnome::Cairo::Matrix )

get-font-options

Retrieves font rendering options set via cairo_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().

method get-font-options ( cairo_font_options_t $options )

cairo_font_options_t $options; a cairo_t

get-group-target

Gets the current destination surface for the context. This is either the original target surface as passed to new(:surface) or 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 always return a valid pointer, but the result can be a “nil” surface if this context is already in an error state, (ie. $context.status() ≠ CAIRO_STATUS_SUCCESS). A nil surface is indicated by Gnome::Cairo::Surface.status() ≠ CAIRO_STATUS_SUCCESS.

Return value: the target surface. This object is owned by cairo. To keep a reference to it, you must call surface-reference().

method get-group-target ( --> Gnome::Cairo::Surface )

get-line-cap

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

Return value: the current line cap style.

method get-line-cap ( --> cairo_line_cap_t )

get-line-join

Gets the current line join style, as set by set-line-join(). Return value: the current line join style.

method get-line-join ( --> cairo_line_join_t )

get-line-width

This function returns the current line width value exactly 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().

Return value: the current line width.

method get-line-width ( --> Num )

get-matrix

Stores the current transformation matrix (CTM) into matrix.

method get-matrix ( --> Gnome::Cairo::Matrix )

get-miter-limit

Gets the current miter limit, as set by set-miter-limit().

Return value: the current miter limit.

method get-miter-limit ( --> Num )

get-operator

Gets the current compositing operator for a cairo context. Return value: the current compositing operator.

method get-operator ( --> cairo_operator_t )

get-scaled-font

Gets the current scaled font for a cairo_t.

Return value: the current scaled font. This object is owned by cairo.

This function never returns Any. If memory cannot be allocated, a special “nil” cairo_scaled_font_t object will be returned on which scaled-font-status() returns CAIRO_STATUS_NO_MEMORY. Using this nil object will cause its error state to propagate to other objects it is passed to, (for example, calling set-scaled-font() with a nil font will trigger an error that will shutdown the cairo_t object).

method get-scaled-font ( --> Gnome::Cairo::ScaledFont )

get-source

Gets the current source pattern for this context.

Return value: the current source pattern. This object is owned by cairo.

method get-source ( --> Gnome::Cairo::Pattern )

get-target

Gets the target surface for the cairo context as passed to create(). This function will always return a valid pointer, but the result can be a “nil” surface if this context is already in an error state, (ie. status() != CAIRO_STATUS_SUCCESS). A nil surface is indicated by surface-status() != CAIRO_STATUS_SUCCESS. Return value: the target surface. This object is owned by cairo. To keep a reference to it, you must call surface-reference().

method get-target ( --> Gnome::Cairo::Surface )

get-tolerance

Gets the current tolerance value, as set by set-tolerance().

Return value: the current tolerance value.

method get-tolerance ( --> Num )

glyph-extents

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).

method glyph-extents (
  cairo_glyph_t $glyphs, Int $num_glyphs,
  cairo_text_extents_t $extents
)

$glyphs; an array of glyph-t objects
$num_glyphs; the number of elements in glyphs
$extents; a text-extents-t object into which the results will be stored

glyph-path

Adds closed paths for the glyphs to the current path. The generated path if filled, achieves an effect similar to that of show-glyphs().

method glyph-path ( cairo_glyph_t $glyphs, Int $num_glyphs )

$glyphs; array of glyphs to show
$num_glyphs; number of glyphs to show

has-current-point

Returns whether a current point is defined on the current path. See get-current-point() for details on the current point.

Return value: whether a current point is defined.

method has-current-point ( --> Bool )

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.

method identity-matrix ( )

in-clip

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.

See clip(), and clip-preserve().

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

method in-clip ( Num() $x, Num() $y --> Bool )

$x; X coordinate of the point to test
$y; Y coordinate of the point to test

in-fill

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.

See fill(), set-fill-rule() and fill-preserve().

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

method in-fill ( Num() $x, Num() $y --> Bool )

$x; X coordinate of the point to test
$y; Y coordinate of the point to test

in-stroke

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. See stroke(), set-line-width(), set-line-join(), set-line-cap(), set-dash(), and stroke-preserve(). Return value: A non-zero value if the point is inside, or zero if outside.

method in-stroke ( Num() $x, Num() $y --> Bool )

$x; X coordinate of the point to test
$y; Y coordinate of the point to test

line-to

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 cairo_move_to(this context, x, y).

method line-to ( Num() $x, Num() $y )

$x; the X coordinate of the end of the new line
$y; the Y coordinate of the end of the new line

mask

A drawing operator that paints the current source using the alpha channel of pattern as a mask. (Opaque areas of pattern are painted with the source, transparent areas are not painted.)

method mask ( cairo_pattern_t $pattern )

$pattern; a pattern

mask-surface

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.)

method mask-surface (
  cairo_surface_t $surface, Num() $surface_x, Num() $surface_y
)

$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

move-to

Begin a new sub-path. After this call the current point will be (x, y).

method move-to ( Num() $x, Num() $y )

$x; the X coordinate of the new position
$y; the Y coordinate of the new position

new-path

Clears the current path. After this call there will be no path and no current point.

method new-path ( )

new-sub-path

Begin a new sub-path.

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 sub-paths are frequently started with move-to().

A call to new-sub-path() is particularly useful when beginning a new sub-path 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().

method new-sub-path ( )

paint

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

method paint ( )

paint-with-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.

method paint-with-alpha ( Num() $alpha )

$alpha; alpha value, between 0 (transparent) and 1 (opaque)

path-extents

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 CAIRO_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().

method path-extents ( --> List )

List returns;

Num; left of the resulting extents
Num; top of the resulting extents
Num; right of the resulting extents
Num; bottom of the resulting extents

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.

Return value: a newly created (surface) pattern containing the results of all drawing operations performed to the group. The caller owns the returned object and should call clear-object() when finished with it.

method pop-group ( --> Gnome::Cairo::Pattern )

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:

my Gnome::Cairo::Pattern $group = $cairo.pop-group;
$cairo.set-source($group);
$group.clear-object;

but is more convenient as there 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.

method pop-group-to-source ( )

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 CAIRO_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:

  my Gnome::Cairo::Pattern $fill-pattern = …
  my Gnome::Cairo::Pattern $stroke-pattern = …
  my Num() $alpha = 0.8;

  with $cairo {
    .push-group;
    .set-source($fill-pattern);
    .fill-preserve;
    .set-source($stroke-pattern);
    .stroke;
    .pop-group-to-source;
    .paint-with-alpha($alpha);
  }

  method push-group ( )

push-group-with-content

The group will have a content type of $content. 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.

method push-group-with-content ( cairo_content_t $content )

$content; a content-t indicating the type of group that will be created

rectangle

Adds a closed sub-path rectangle of the given size to the current path at position ($x, $y) in user-space coordinates. This method is logically equivalent to:

  with $cairo {
    .move-to( $x, $y);
    .rel-line-to( $width, 0);
    .rel-line-to( 0, $height);
    .rel-line-to( -$width, 0);
    .close.path;
  }

  method rectangle ( Num() $x, Num() $y, Num() $width, Num() $height )

$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

rel-curve-to

Relative-coordinate version of curve-to(). All offsets are relative to the current point. Adds a cubic Bézier 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), then 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).

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

method rel-curve-to (
  Num() $dx1, Num() $dy1, Num() $dx2, Num() $dy2,
  Num() $dx3, Num() $dy3
)

$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

rel-line-to

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).

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

method rel-line-to ( Num() $dx, Num() $dy )

$dx; the X offset to the end of the new line
$dy; the Y offset to the end of the new line

rel-move-to

Begin a new sub-path. 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).

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

method rel-move-to ( Num() $dx, Num() $dy )

$dx; the X offset
$dy; the Y offset

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.

method reset-clip ( )

restore

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

method restore ( )

rotate

Modifies the current transformation matrix (CTM) by rotating the user-space axes by $angle radians. The rotation of the axes takes place after any existing transformation of user space. The rotation direction for positive angles is from the positive X axis toward the positive Y axis.

method rotate ( Num() $angle )

$angle; Angle to rotate in radians

save

Makes a copy of the current state of this context and saves it on an internal stack of saved states for this context. When restore() is called, this context 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().

method save ( )

scale

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.

method scale ( Num() $sx, Num() $sy )

$sx; scale factor for the X dimension
$sy; scale factor for the Y dimension

select-font-face

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.

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.

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 $family 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.

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.

method select-font-face (
  Str $family, cairo_font_slant_t $slant,
  cairo_font_weight_t $weight
)

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

set-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 font-options-set-antialias().

method set-antialias ( cairo_antialias_t $antialias )

$antialias; the new antialiasing mode

set-dash

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 length of alternate “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 $num_dashes is 0 dashing is disabled. If num_dashes is 1 a symmetric pattern is assumed with alternating on and off portions of the size specified by the single value in $dashes.

If any value in $dashes is negative, or if all values are 0, then this context will be put into an error state with a status of CAIRO_STATUS_INVALID_DASH.

method set-dash ( Array $dashes, Num() $offset )

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

set-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 cairo_fill_rule_t for details on the semantics of each available fill rule.

The default fill rule is CAIRO_FILL_RULE_WINDING.

method set-fill-rule ( cairo_fill_rule_t $fill_rule )

$fill_rule; a fill rule type

set-font-face

Replaces the current cairo_font_face_t object in the cairo_t with font_face. The replaced font face in the cairo_t will be destroyed if there are no other references to it.

method set-font-face ( cairo_font_face_t $font_face )

$font_face; a font-face-t, or Any to restore to the default font

set-font-matrix

Sets the current font matrix to matrix. 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

method set-font-matrix ( cairo_matrix_t $matrix )

$matrix; a matrix-t describing a transform to be applied to the current font.

set-font-options

Sets a set of custom font rendering options for the cairo_t. 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.

method set-font-options ( cairo_font_options_t $options )

$options; font options to use

set-font-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 $size by $size square in user space.)

If text is drawn without a call to set-font-size(), (nor set-font-matrix() nor cset-scaled-font()), the default font size is 10.0.

method set-font-size ( Num() $size )

$size; The size of the current font

set-line-cap

Sets the current line cap style within the cairo context. See cairo_line_cap_t 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.

method set-line-cap ( Int $line_cap )

$line_cap; a line cap style

set-line-join

Sets the current line join style within the cairo context. See cairo_line_join_t 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.

method set-line-join ( Int $line_join )

$line_join; a line join style

set-line-width

Sets the current line width within the cairo context. The line width value 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 width 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.

method set-line-width ( Num() $width )

$width; a line width

set-matrix

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

method set-matrix ( cairo_matrix_t $matrix )

$matrix; a transformation matrix from user space to device space

set-miter-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).

method set-miter-limit ( Num() $limit )

$limit; a cairo context

set-operator

Sets the compositing operator to be used for all drawing operations. See cairo_operator_t for details on the semantics of each available compositing operator.

The default operator is CAIRO_OPERATOR_OVER.

method set-operator ( cairo_operator_t $op )

$op; a compositing operator

set-scaled-font

Replaces the current font face, font matrix, and font options in the cairo_t with those of the cairo_scaled_font_t. Except for some translation, the current CTM of the cairo_t should be the same as that of the cairo_scaled_font_t, which can be accessed using scaled-font-get-ctm().

method set-scaled-font ( cairo_scaled_font_t $scaled_font )

$scaled_font; a scaled font

set-source

Sets the source pattern within this 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. See pattern-set-matrix().

The default source pattern is a solid pattern that is opaque black, (that is, it is equivalent to set-source-rgb( 0.0, 0.0, 0.0)).

method set-source ( cairo_pattern_t $source )

$source; a pattern type to be used as the source for subsequent drawing operations.

set-source-pixbuf

Sets the given pixbuf as the source pattern for this context.

The image is aligned so that the origin of the $pixbuf is ($x, $y).

method set-source-pixbuf( $pixbuf is copy, Num() $x, Num() $y ) {

$pixbuf; The pixel buffer
$x; x origin
$y; y origin

set-source-rgb

Sets the source pattern within this 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.

The default source pattern is opaque black, (that is, it is equivalent to set-source-rgb( 0.0, 0.0, 0.0)).

method set-source-rgb ( Num() $red, Num() $green, Num() $blue )

$red; red component of color
$green; green component of color
$blue; blue component of color

set-source-rgba

Sets the source pattern within this 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.

The default source pattern is opaque black, (that is, it is equivalent to set-source-rgba( 0.0, 0.0, 0.0, 1.0)).

method set-source-rgba (
  Num() $red, Num() $green, Num() $blue, Num() $alpha
)

$red; red component of color
$green; green component of color
$blue; blue component of color
$alpha; alpha component of color

set-source-surface

This is a convenience function for creating a pattern from $surface and setting it as the source in this context with set-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 parameters 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 Gnome::Cairo::Pattern.new(:surface). 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 Gnome::Cairo::Pattern.set-extend()).

method set-source-surface ( cairo_surface_t $surface, Num() $x, Num() $y )

$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

set-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 $tolerance is restricted to the smallest representable internal value.

method set-tolerance ( Num() $tolerance )

$tolerance; the tolerance, in device units

show-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.

method show-glyphs ( Array $glyphs )

$glyphs; array of glyphs to show
$num_glyphs; number of glyphs to show

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 Gnome::Cairo::Surface.show-page() on this context’s target surface.

method show-page ( )

show-text

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.

method show-text ( Str $utf8-string )

$utf8-string; a string to show

show-text-glyphs

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 clusters. 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_text_cluster_t for constraints on valid clusters.

method show-text-glyphs (
  Str $utf8, Array $glyphs, Array $clusters,
  cairo_text_cluster_flags_t $cluster_flags
)

$utf8; a string of text encoded in UTF-8.
$glyphs; array of glyphs to show. Element type cairo_glyph_t.
$clusters; array of cluster mapping information. Element type cairo_text_cluster_t.
$cluster_flags; cluster mapping flags.

status

Checks whether an error has previously occurred for this context.

Returns: the current status of this context, see cairo_status_t

method status ( --> cairo_status_t )

status-to-string

Provides a human-readable description of a cairo_status_t.

method status-to-string ( cairo_status_t $status --> Str )

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 set-line-width(), set-line-join(), cset-line-cap(), set-dash(), and stroke-preserve().

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

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.
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.

method stroke ( )

stroke-extents

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. See stroke(), set-line-width(), set-line-join(), set-line-cap(), set-dash(), and stroke-preserve().

method stroke-extents ( --> List )

List returns;

Num; left of the resulting extents
Num; top of the resulting extents
Num; right of the resulting extents
Num; bottom of the resulting extents

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 set-line-width(), set-line-join(), set-line-cap(), set-dash(), and stroke-preserve().

method stroke-preserve ( )

tag-begin

Marks the beginning of the t$ag-name structure. Call tag-end() with the same $tag-name to mark the end of the structure.

The $attributes string is of the form “key1=value2 key2=value2 …”. Values may be boolean (true/false or 1/0), integer, float, string, or an array. String values are enclosed in single quotes (‘). Single quotes and backslashes inside the string should be escaped with a backslash. Boolean values may be set to true by only specifying the key. E.g. the attribute string “key” is the equivalent to “key=true”. Arrays are enclosed in ‘[]’. E.g. “rect=[1.2 4.3 2.0 3.0]”.

If no attributes are required, attributes can be an empty string or NULL. Invalid nesting of tags or invalid attributes will cause this context to shutdown with a status of CAIRO_STATUS_TAG_ERROR.

For example;

with $cairo {
  .tag-begin( CAIRO_TAG_LINK, "uri='https://cairographics.org'");
  .move-to( 50, 50);
  .show-text('This is a link to the cairo website.');
  .tag-end(CAIRO_TAG_LINK);
}

See tag-end().

method tag-begin ( Str $tag_name, Str $attributes )

$tag-name; The tag name. This can only be one of CAIRO_TAG_LINK or CAIRO_TAG_DEST.
$attributes; tag attributes.

tag-end

Marks the end of the tag_name structure. Invalid nesting of tags will cause this context to shutdown with a status of CAIRO_STATUS_TAG_ERROR. See tag-begin().

method tag-end ( Str $tag_name )

$tag_name; tag name. This can only be one of CAIRO_TAG_LINK or CAIRO_TAG_DEST.

text-extents

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.

method text-extents ( Str $utf-string --> cairo_text_extents_t )

$utf8;
cairo_text_extents_t $extents; a NUL-terminated string of text encoded in UTF-8, or Any

text-path

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.

method text-path ( Str $utf8 )

$utf8; a string of text encoded in UTF-8.

transform

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.

method transform ( cairo_matrix_t $matrix )

$matrix; a transformation to be applied to the user-space axes

translate

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.

method translate ( Num() $tx, Num() $ty )

$tx; amount to translate in the X direction
$ty; amount to translate in the Y direction

user-to-device

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

method user-to-device ( Num() $x is rw, Num() $y is rw )

$x; X value of coordinate
$y; Y value of coordinate

user-to-device-distance

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).

method user-to-device-distance ( Num() $dx is rw, Num() $dy is rw )

$dx; X component of a distance vector
$dy; Y component of a distance vector

Gnome::Cairo

Description

See Also

Synopsis

Declaration

Methods

new

:surface

:native-object

append-path

arc

arc-negative

clip

clip-extents

clip-preserve

close-path

copy-clip-rectangle-list

copy-page

copy-path

copy-path-flat

curve-to

device-to-user

device-to-user-distance

fill

fill-extents

fill-preserve

get-antialias

get-current-point

get-dash

get-dash-count

get-fill-rule

get-font-face

get-font-matrix

get-font-options

get-group-target

get-line-cap

get-line-join

get-line-width

get-matrix

get-miter-limit

get-operator

get-scaled-font

get-source

get-target

get-tolerance

glyph-extents

glyph-path

has-current-point

identity-matrix

in-clip

in-fill

in-stroke

line-to

mask

mask-surface

move-to

new-path

new-sub-path

paint

paint-with-alpha

path-extents

pop-group

pop-group-to-source

push-group

push-group-with-content

rectangle

rel-curve-to

rel-line-to

rel-move-to

reset-clip

restore

rotate

save

scale

select-font-face

set-antialias

set-dash

set-fill-rule

set-font-face

set-font-matrix