cairo_t

typedef struct _cairo cairo_t;

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

cairo_create ()

cairo_t*    cairo_create                    (cairo_surface_t *target);

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 cairo_image_surface_create() (or any other cairo_<backend>_surface_create variant).

This function references target, so you can immediately call cairo_surface_destroy() on it if you don't need to maintain a separate reference to it.

cairo_reference ()

cairo_t*    cairo_reference                 (cairo_t *cr);

Increases the reference count on cr by one. This prevents cr from being destroyed until a matching call to cairo_destroy() is made.

cairo_destroy ()

void        cairo_destroy                   (cairo_t *cr);

Decreases the reference count on cr by one. If the result is zero, then cr and all associated resources are freed. See cairo_reference().

cairo_status ()

cairo_status_t cairo_status                 (cairo_t *cr);

Checks whether an error has previously occurred for this context.

cairo_save ()

void        cairo_save                      (cairo_t *cr);

Makes a copy of the current state of cr and saves it on an internal stack of saved states for cr. When cairo_restore() is called, cr will be restored to the saved state. Multiple calls to cairo_save() and cairo_restore() can be nested; each call to cairo_restore() restores the state from the matching paired cairo_save().

It isn't necessary to clear all saved states before a cairo_t is freed. If the reference count of a cairo_t drops to zero in response to a call to cairo_destroy(), any saved states will be freed along with the cairo_t.

cairo_restore ()

void        cairo_restore                   (cairo_t *cr);

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

cairo_get_target ()

cairo_surface_t* cairo_get_target           (cairo_t *cr);

Gets the target surface for the cairo context as passed to cairo_create().

This function will always return a valid pointer, but the result can be a "nil" surface if cr is already in an error state, (ie. cairo_status() != CAIRO_STATUS_SUCCESS). A nil surface is indicated by cairo_surface_status() != CAIRO_STATUS_SUCCESS.

cairo_push_group ()

void        cairo_push_group                (cairo_t *cr);

Temporarily redirects drawing to an intermediate surface known as a group. The redirection lasts until the group is completed by a call to cairo_pop_group() or cairo_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 cairo_push_group()/cairo_pop_group(). Each call pushes/pops the new target group onto/from a stack.

The cairo_push_group() function calls cairo_save() so that any changes to the graphics state will not be visible outside the group, (the pop_group functions call cairo_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 cairo_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:

cairo_push_group (cr);
cairo_set_source (cr, fill_pattern);
cairo_fill_preserve (cr);
cairo_set_source (cr, stroke_pattern);
cairo_stroke (cr);
cairo_pop_group_to_source (cr);
cairo_paint_with_alpha (cr, alpha);

Since 1.2

cairo_push_group_with_content ()

void        cairo_push_group_with_content   (cairo_t *cr,
                                             cairo_content_t content);

Temporarily redirects drawing to an intermediate surface known as a group. The redirection lasts until the group is completed by a call to cairo_pop_group() or cairo_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 content. The ability to control this content type is the only distinction between this function and cairo_push_group() which you should see for a more detailed description of group rendering.

Since 1.2

cairo_pop_group ()

cairo_pattern_t* cairo_pop_group            (cairo_t *cr);

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

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

Since 1.2

cairo_pop_group_to_source ()

void        cairo_pop_group_to_source       (cairo_t *cr);

Terminates the redirection begun by a call to cairo_push_group() or cairo_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:

cairo_pattern_t *group = cairo_pop_group (cr);
cairo_set_source (cr, group);
cairo_pattern_destroy (group);

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

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

Since 1.2

cairo_get_group_target ()

cairo_surface_t* cairo_get_group_target     (cairo_t *cr);

Gets the target surface for the current group as started by the most recent call to cairo_push_group() or cairo_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 cairo_pop_group() or cairo_pop_group_to_source()).

Since 1.2

cairo_set_source_rgb ()

void        cairo_set_source_rgb            (cairo_t *cr,
                                             double red,
                                             double green,
                                             double blue);

Sets the source pattern within cr 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.

cairo_set_source_rgba ()

void        cairo_set_source_rgba           (cairo_t *cr,
                                             double red,
                                             double green,
                                             double blue,
                                             double alpha);

Sets the source pattern within cr 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.

cairo_set_source ()

void        cairo_set_source                (cairo_t *cr,
                                             cairo_pattern_t *source);

Sets the source pattern within cr 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 cairo_set_source(). This means that further modifications of the current transformation matrix will not affect the source pattern. See cairo_pattern_set_matrix().

XXX: I'd also like to direct the reader's attention to some (not-yet-written) section on cairo's imaging model. How would I do that if such a section existed? (cworth).

cairo_set_source_surface ()

void        cairo_set_source_surface        (cairo_t *cr,
                                             cairo_surface_t *surface,
                                             double x,
                                             double y);

This is a convenience function for creating a pattern from surface and setting it as the source in cr with cairo_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 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 cairo_pattern_create_for_surface(). The resulting pattern can be queried with cairo_get_source() so that these attributes can be modified if desired, (eg. to create a repeating pattern with cairo_pattern_set_extend()).

cairo_get_source ()

cairo_pattern_t* cairo_get_source           (cairo_t *cr);

Gets the current source pattern for cr.

enum cairo_antialias_t

typedef enum _cairo_antialias {
    CAIRO_ANTIALIAS_DEFAULT,
    CAIRO_ANTIALIAS_NONE,
    CAIRO_ANTIALIAS_GRAY,
    CAIRO_ANTIALIAS_SUBPIXEL
} cairo_antialias_t;

Specifies the type of antialiasing to do when rendering text or shapes.

cairo_set_antialias ()

void        cairo_set_antialias             (cairo_t *cr,
                                             cairo_antialias_t 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 cairo_font_options_set_antialias().

cairo_get_antialias ()

cairo_antialias_t cairo_get_antialias       (cairo_t *cr);

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

cairo_set_dash ()

void        cairo_set_dash                  (cairo_t *cr,
                                             const double *dashes,
                                             int num_dashes,
                                             double offset);

Sets the dash pattern to be used by cairo_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 cairo_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 cairo_t will be put into an error state with a status of CAIRO_STATUS_INVALID_DASH.

enum cairo_fill_rule_t

typedef enum _cairo_fill_rule {
    CAIRO_FILL_RULE_WINDING,
    CAIRO_FILL_RULE_EVEN_ODD
} cairo_fill_rule_t;

cairo_fill_rule_t is used to select how paths are filled. For both fill rules, whether or not a point is included in the fill is determined by taking a ray from that point to infinity and looking at intersections with the path. The ray can be in any direction, as long as it doesn't pass through the end point of a segment or have a tricky intersection such as intersecting tangent to the path. (Note that filling is not actually implemented in this way. This is just a description of the rule that is applied.)

New entries may be added in future versions.

cairo_set_fill_rule ()

void        cairo_set_fill_rule             (cairo_t *cr,
                                             cairo_fill_rule_t 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 cairo_fill and cairo_clip. See cairo_fill_rule_t for details on the semantics of each available fill rule.

cairo_get_fill_rule ()

cairo_fill_rule_t cairo_get_fill_rule       (cairo_t *cr);

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

enum cairo_line_cap_t

typedef enum _cairo_line_cap {
    CAIRO_LINE_CAP_BUTT,
    CAIRO_LINE_CAP_ROUND,
    CAIRO_LINE_CAP_SQUARE
} cairo_line_cap_t;

enumeration for style of line-endings

cairo_set_line_cap ()

void        cairo_set_line_cap              (cairo_t *cr,
                                             cairo_line_cap_t 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 cairo_stroke(), cairo_stroke_extents(), and cairo_stroke_to_path(), but does not have any effect during path construction.

cairo_get_line_cap ()

cairo_line_cap_t cairo_get_line_cap         (cairo_t *cr);

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

enum cairo_line_join_t

typedef enum _cairo_line_join {
    CAIRO_LINE_JOIN_MITER,
    CAIRO_LINE_JOIN_ROUND,
    CAIRO_LINE_JOIN_BEVEL
} cairo_line_join_t;

cairo_set_line_join ()

void        cairo_set_line_join             (cairo_t *cr,
                                             cairo_line_join_t 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 cairo_stroke(), cairo_stroke_extents(), and cairo_stroke_to_path(), but does not have any effect during path construction.

cairo_get_line_join ()

cairo_line_join_t cairo_get_line_join       (cairo_t *cr);

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

cairo_set_line_width ()

void        cairo_set_line_width            (cairo_t *cr,
                                             double 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 cairo_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 cairo_set_line_with() and the stroking operation, then one can just pass user-space values to cairo_set_line_width() and ignore this note.

As with the other stroke parameters, the current line width is examined by cairo_stroke(), cairo_stroke_extents(), and cairo_stroke_to_path(), but does not have any effect during path construction.

The default line width value is 2.0.

cairo_get_line_width ()

double      cairo_get_line_width            (cairo_t *cr);

cairo_set_miter_limit ()

void        cairo_set_miter_limit           (cairo_t *cr,
                                             double limit);

cairo_get_miter_limit ()

double      cairo_get_miter_limit           (cairo_t *cr);

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

enum cairo_operator_t

typedef enum _cairo_operator {
    CAIRO_OPERATOR_CLEAR,

    CAIRO_OPERATOR_SOURCE,
    CAIRO_OPERATOR_OVER,
    CAIRO_OPERATOR_IN,
    CAIRO_OPERATOR_OUT,
    CAIRO_OPERATOR_ATOP,

    CAIRO_OPERATOR_DEST,
    CAIRO_OPERATOR_DEST_OVER,
    CAIRO_OPERATOR_DEST_IN,
    CAIRO_OPERATOR_DEST_OUT,
    CAIRO_OPERATOR_DEST_ATOP,

    CAIRO_OPERATOR_XOR,
    CAIRO_OPERATOR_ADD,
    CAIRO_OPERATOR_SATURATE
} cairo_operator_t;

cairo_set_operator ()

void        cairo_set_operator              (cairo_t *cr,
                                             cairo_operator_t op);

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.

XXX: I'd also like to direct the reader's attention to some (not-yet-written) section on cairo's imaging model. How would I do that if such a section existed? (cworth).

cairo_get_operator ()

cairo_operator_t cairo_get_operator         (cairo_t *cr);

Gets the current compositing operator for a cairo context.

cairo_set_tolerance ()

void        cairo_set_tolerance             (cairo_t *cr,
                                             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.)

cairo_get_tolerance ()

double      cairo_get_tolerance             (cairo_t *cr);

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

cairo_clip ()

void        cairo_clip                      (cairo_t *cr);

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

After cairo_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 cairo_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 cairo_clip() within a cairo_save()/cairo_restore() pair. The only other means of increasing the size of the clip region is cairo_reset_clip().

cairo_clip_preserve ()

void        cairo_clip_preserve             (cairo_t *cr);

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

Unlike cairo_clip(), cairo_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 cairo_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 cairo_clip() within a cairo_save()/cairo_restore() pair. The only other means of increasing the size of the clip region is cairo_reset_clip().

cairo_reset_clip ()

void        cairo_reset_clip                (cairo_t *cr);

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 cairo_reset_clip() as it will cause results unexpected by higher-level code which calls cairo_clip(). Consider using cairo_save() and cairo_restore() around cairo_clip() as a more robust means of temporarily restricting the clip region.

cairo_fill ()

void        cairo_fill                      (cairo_t *cr);

A drawing operator that fills the current path according to the current fill rule, (each sub-path is implicitly closed before being filled). After cairo_fill, the current path will be cleared from the cairo context. See cairo_set_fill_rule() and cairo_fill_preserve().

cairo_fill_preserve ()

void        cairo_fill_preserve             (cairo_t *cr);

A drawing operator that fills the current path according to the current fill rule, (each sub-path is implicitly closed before being filled). Unlike cairo_fill(), cairo_fill_preserve preserves the path within the cairo context.

See cairo_set_fill_rule() and cairo_fill().

cairo_fill_extents ()

void        cairo_fill_extents              (cairo_t *cr,
                                             double *x1,
                                             double *y1,
                                             double *x2,
                                             double *y2);

cairo_in_fill ()

cairo_bool_t cairo_in_fill                  (cairo_t *cr,
                                             double x,
                                             double y);

Tests whether the given point is inside the area that would be filled by doing a cairo_fill() operation on cr given the current path and filling parameters.

See cairo_fill(), cairo_set_fill_rule() and cairo_fill_preserve().

cairo_mask ()

void        cairo_mask                      (cairo_t *cr,
                                             cairo_pattern_t *pattern);

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.)

cairo_mask_surface ()

void        cairo_mask_surface              (cairo_t *cr,
                                             cairo_surface_t *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.)

cairo_paint ()

void        cairo_paint                     (cairo_t *cr);

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

cairo_paint_with_alpha ()

void        cairo_paint_with_alpha          (cairo_t *cr,
                                             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 cairo_paint(), but the drawing is faded out using the alpha value.

cairo_stroke ()

void        cairo_stroke                    (cairo_t *cr);

A drawing operator that strokes the current path according to the current line width, line join, line cap, and dash settings. After cairo_stroke, the current path will be cleared from the cairo context. See cairo_set_line_width(), cairo_set_line_join(), cairo_set_line_cap(), cairo_set_dash(), and cairo_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 cairo_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 cairo_move_to() followed by either a cairo_close_path() or one or more calls to cairo_line_to() to the same coordinate as the cairo_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.

cairo_stroke_preserve ()

void        cairo_stroke_preserve           (cairo_t *cr);

A drawing operator that strokes the current path according to the current line width, line join, line cap, and dash settings. Unlike cairo_stroke(), cairo_stroke_preserve preserves the path within the cairo context.

See cairo_set_line_width(), cairo_set_line_join(), cairo_set_line_cap(), cairo_set_dash(), and cairo_stroke_preserve().

cairo_stroke_extents ()

void        cairo_stroke_extents            (cairo_t *cr,
                                             double *x1,
                                             double *y1,
                                             double *x2,
                                             double *y2);

cairo_in_stroke ()

cairo_bool_t cairo_in_stroke                (cairo_t *cr,
                                             double x,
                                             double y);

Tests whether the given point is inside the area that would be stroked by doing a cairo_stroke() operation on cr given the current path and stroking parameters.

See cairo_stroke(), cairo_set_line_width(), cairo_set_line_join(), cairo_set_line_cap(), cairo_set_dash(), and cairo_stroke_preserve().

cairo_copy_page ()

void        cairo_copy_page                 (cairo_t *cr);

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

cairo_show_page ()

void        cairo_show_page                 (cairo_t *cr);

Emits and clears the current page for backends that support multiple pages. Use cairo_copy_page() if you don't want to clear the page.