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This manual documents MIT/GNU Scheme Pucked Cairo 0.13.
Copyright © 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019 Matthew Birkholz
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”
| • Introduction: | ||
| • API Reference: | ||
| • GNU Free Documentation License: |
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The Cairo system is a collection of Scheme data types and procedures providing a Schemely interface to the Cairo 2D vector graphics library. Very little of the library’s API has been wrapped — just what is listed herein. As one might expect of a “Schemely” interface, all toolkit resources are protected from “leaking” by the garbage collector. When Scheme’s representative of a toolkit resource is dropped and collected, the toolkit resource is freed, just as the C/Unix FFI’s malloced aliens are automatically freed.
The Cairo library is thread-safe assuming threads do not operate simultaneously on the same objects (contexts, patterns, surfaces). Implicit global state is protected by mutexes. Some Cairo procedures involve GLib objects like PangoLayouts, which should not be used unless GLib is locked, else many warning lines will be written to stderr. See with-glib-lock in GLib Plugin Manual.
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| • Cairo Context: | ||
| • Cairo Surface: | ||
| • Cairo Pattern: |
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This simple wrapper for cairo_t objects ensures that the
toolkit object is de-referenced when the Scheme object is garbage
collected. The Scheme object is an alien of type cairo_t.
Creates a new cairo context with all graphics state parameters set to
default values and with surface as the target surface. The
context will reference the surface so cairo-surface-destroy can
be called on it if the surface will no longer be used directly.
De-references a cairo context object. Further operations on cairo will produce an error.
Sets the source pattern within cairo to color which will then be used for future drawing operations. The default source pattern is opaque black. See colors.
Sets the source pattern within cairo to pattern which will then be used for future drawing operations. The default source is solid, opaque black.
Modifies the current transformation matrix of cairo by translating the user-space origin to (dx, dy).
Modifies the current transformation matrix of cairo by scaling the X and Y user-space axes by sx and sy respectively.
Begin a new sub-path. After this call cairo’s current point will be (x, y).
Begins a new sub-path. Note that cairo’s 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 cairo-move-to.
A call to cairo-new-sub-path is particularly useful when
beginning a new sub-path with one of the cairo-arc calls. This
makes things easier as it is no longer necessary to manually compute
the arc’s initial coordinates for a call to cairo-move-to.
Adds a circular arc to the current path. The arc is centered at (x, y), has radius, begins at start and proceeds in the direction of increasing angles to end. If end is less than start it will be progressively increased by 2pi until it is greater than start.
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
cairo-new-sub-path before calling cairo-arc.
Start and end should be given in radians. An angle of 0.0 is in the direction of the positive X axis (in user space). An angle of pi/2 radians (90 degrees) is in the direction of the positive Y axis (in user space). With the default transformation matrix, angles increase in a clockwise direction.
Paints the current source everywhere within the current clip region.
Strokes cairo’s current path according to the current line width, line join, line cap, and dash settings. The current path is then cleared.
Fills cairo’s current path according to the current fill rule. Each sub-path is implicitly closed before being filled. The current path is then cleared.
Calls receiver with the user-space bounding box of the area inside cairo’s current clip. Receiver will be called with four flonums: the left, top, right and bottom bounds of the clip.
Sets cairo’s current font matrix to matrix, which 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. Matrix should be
created using cairo-matrix.
Creates a Cairo transformation matrix. A point (x,y) is
transformed by this matrix into (xx * x + xy * y + x0, yx * x +
yy * y + y0).
Colors are floating-vectors containing four flonums between 0. and
1. inclusive: the red, green, blue and alpha components. For example
#[floating-vector 42 0. 1. 0. 1.] represents completely opaque
green.
Colors can also be created by Pango’s ->color procedure
when applied to a string in a number of formats, e.g. "blue" or
"#00F" or "rgba(0,0,100%,1)".
See ->color in Pango Plugin Manual.
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This simple wrapper for cairo_surface_t objects ensures that the
toolkit object is de-referenced when the Scheme object is garbage
collected. The Scheme object is an alien of type
cairo_surface_t.
Creates a Cairo image surface widthxheight pixels.
Writes surface to a new file filename as a PNG image.
Does any pending drawing for surface. Also restores any temporary modifications Cairo has made to the surface’s state.
De-references a cairo surface object. Further operations on surface will produce an error.
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This simple wrapper for cairo_pattern_t objects ensures that the
toolkit object is de-referenced when the Scheme object is garbage
collected. The Scheme object is an alien of type
cairo_pattern_t.
Creates a new radial gradient pattern from the circle defined by
(x0, y0, radius0) to a second circle defined by
(x1, y1, radius1). Before using the gradient
pattern, a number of color stops should be defined using
cairo-pattern-add-color-stop.
Creates a new linear gradient pattern along the line from (x0,
y0) to (x1, y1). Before using the gradient pattern,
a number of color stops should be defined using
cairo-pattern-add-color-stop.
Adds a color stop to a gradient pattern. Offset specifies the location along the gradient’s control vector. Color should be an RGBA color. See colors. If two (or more) stops are specified with identical offset values, they will be sorted according to the order in which the stops are added. Stops added earlier will compare less than stops added later. This can be useful for reliably making sharp color transitions instead of the typical blend.
De-references a cairo pattern object. Further operations on pattern will produce an error.
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