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Cairo: A Vector Graphics Library | ![]() |
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Top | Description |
typedef cairo_t; cairo_t * cairo_create (cairo_surface_t *target); cairo_t * cairo_reference (cairo_t *cr); void cairo_destroy (cairo_t *cr); cairo_status_t cairo_status (cairo_t *cr); void cairo_save (cairo_t *cr); void cairo_restore (cairo_t *cr); cairo_surface_t * cairo_get_target (cairo_t *cr); void cairo_push_group (cairo_t *cr); void cairo_push_group_with_content (cairo_t *cr, cairo_content_t content); cairo_pattern_t * cairo_pop_group (cairo_t *cr); void cairo_pop_group_to_source (cairo_t *cr); cairo_surface_t * cairo_get_group_target (cairo_t *cr); void cairo_set_source_rgb (cairo_t *cr, double red, double green, double blue); void cairo_set_source_rgba (cairo_t *cr, double red, double green, double blue, double alpha); void cairo_set_source (cairo_t *cr, cairo_pattern_t *source); void cairo_set_source_surface (cairo_t *cr, cairo_surface_t *surface, double x, double y); cairo_pattern_t * cairo_get_source (cairo_t *cr); enum cairo_antialias_t; void cairo_set_antialias (cairo_t *cr, cairo_antialias_t antialias); cairo_antialias_t cairo_get_antialias (cairo_t *cr); void cairo_set_dash (cairo_t *cr, const double *dashes, int num_dashes, double offset); int cairo_get_dash_count (cairo_t *cr); void cairo_get_dash (cairo_t *cr, double *dashes, double *offset); enum cairo_fill_rule_t; void cairo_set_fill_rule (cairo_t *cr, cairo_fill_rule_t fill_rule); cairo_fill_rule_t cairo_get_fill_rule (cairo_t *cr); enum cairo_line_cap_t; void cairo_set_line_cap (cairo_t *cr, cairo_line_cap_t line_cap); cairo_line_cap_t cairo_get_line_cap (cairo_t *cr); enum cairo_line_join_t; void cairo_set_line_join (cairo_t *cr, cairo_line_join_t line_join); cairo_line_join_t cairo_get_line_join (cairo_t *cr); void cairo_set_line_width (cairo_t *cr, double width); double cairo_get_line_width (cairo_t *cr); void cairo_set_miter_limit (cairo_t *cr, double limit); double cairo_get_miter_limit (cairo_t *cr); enum cairo_operator_t; void cairo_set_operator (cairo_t *cr, cairo_operator_t op); cairo_operator_t cairo_get_operator (cairo_t *cr); void cairo_set_tolerance (cairo_t *cr, double tolerance); double cairo_get_tolerance (cairo_t *cr); void cairo_clip (cairo_t *cr); void cairo_clip_preserve (cairo_t *cr); void cairo_clip_extents (cairo_t *cr, double *x1, double *y1, double *x2, double *y2); void cairo_reset_clip (cairo_t *cr); cairo_rectangle_t; cairo_rectangle_list_t; void cairo_rectangle_list_destroy (cairo_rectangle_list_t *rectangle_list); cairo_rectangle_list_t * cairo_copy_clip_rectangle_list (cairo_t *cr); void cairo_fill (cairo_t *cr); void cairo_fill_preserve (cairo_t *cr); void cairo_fill_extents (cairo_t *cr, double *x1, double *y1, double *x2, double *y2); cairo_bool_t cairo_in_fill (cairo_t *cr, double x, double y); void cairo_mask (cairo_t *cr, cairo_pattern_t *pattern); void cairo_mask_surface (cairo_t *cr, cairo_surface_t *surface, double surface_x, double surface_y); void cairo_paint (cairo_t *cr); void cairo_paint_with_alpha (cairo_t *cr, double alpha); void cairo_stroke (cairo_t *cr); void cairo_stroke_preserve (cairo_t *cr); void cairo_stroke_extents (cairo_t *cr, double *x1, double *y1, double *x2, double *y2); cairo_bool_t cairo_in_stroke (cairo_t *cr, double x, double y); void cairo_copy_page (cairo_t *cr); void cairo_show_page (cairo_t *cr); unsigned int cairo_get_reference_count (cairo_t *cr); cairo_status_t cairo_set_user_data (cairo_t *cr, const cairo_user_data_key_t *key, void *user_data, cairo_destroy_func_t destroy); void * cairo_get_user_data (cairo_t *cr, const cairo_user_data_key_t *key);
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 cairo_move_to()
and cairo_line_to()
, and then
draw shapes with cairo_stroke()
or cairo_fill()
.
cairo_t's can be pushed to a stack via cairo_save()
.
They may then safely be changed, without loosing the current state.
Use cairo_restore()
to restore to the saved state.
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 contexts, as cairo_t objects are named, are central to cairo and all drawing with cairo is always done to a cairo_t object.
Memory management of cairo_t is done with
cairo_reference()
and cairo_destroy()
.
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.
|
target surface for the context |
Returns : |
a newly allocated cairo_t with a reference
count of 1. The initial reference count should be released
with cairo_destroy() when you are done using the cairo_t.
This function never returns NULL . If memory cannot be
allocated, a special cairo_t object will be returned on
which cairo_status() returns CAIRO_STATUS_NO_MEMORY .
You can use this object normally, but no drawing will
be done.
|
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.
The number of references to a cairo_t can be get using
cairo_get_reference_count()
.
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()
.
|
a cairo_t |
cairo_status_t cairo_status (cairo_t *cr);
Checks whether an error has previously occurred for this context.
|
a cairo context |
Returns : |
the current status of this context, see cairo_status_t |
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.
|
a cairo_t |
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.
|
a cairo_t |
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
.
|
a cairo context |
Returns : |
the target surface. This object is owned by cairo. To
keep a reference to it, you must call cairo_surface_reference() .
|
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);
|
a cairo context |
Since 1.2
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.
|
a cairo context |
|
a %cairo_content_t indicating the type of group that will be created |
Since 1.2
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.
|
a cairo context |
Returns : |
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
cairo_pattern_destroy() when finished with it.
|
Since 1.2
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.
|
a cairo context |
Since 1.2
cairo_surface_t * cairo_get_group_target (cairo_t *cr);
Gets the current destination surface for the context. This is either
the original target surface as passed to cairo_create()
or 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 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
.
|
a cairo context |
Returns : |
the target surface. This object is owned by cairo. To
keep a reference to it, you must call cairo_surface_reference() .
|
Since 1.2
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.
The default source pattern is opaque black, (that is, it is equivalent to cairo_set_source_rgb(cr, 0.0, 0.0, 0.0)).
|
a cairo context |
|
red component of color |
|
green component of color |
|
blue component of color |
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.
The default source pattern is opaque black, (that is, it is equivalent to cairo_set_source_rgba(cr, 0.0, 0.0, 0.0, 1.0)).
|
a cairo context |
|
red component of color |
|
green component of color |
|
blue component of color |
|
alpha component of color |
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()
.
The default source pattern is a solid pattern that is opaque black, (that is, it is equivalent to cairo_set_source_rgb(cr, 0.0, 0.0, 0.0)).
|
a cairo context |
|
a cairo_pattern_t to be used as the source for subsequent drawing operations. |
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()
).
|
a cairo context |
|
a surface to be used to set the source pattern |
|
User-space X coordinate for surface origin |
|
User-space Y coordinate for surface origin |
cairo_pattern_t * cairo_get_source (cairo_t *cr);
Gets the current source pattern for cr
.
|
a cairo context |
Returns : |
the current source pattern. This object is owned by
cairo. To keep a reference to it, you must call
cairo_pattern_reference() .
|
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.
Use the default antialiasing for the subsystem and target device | |
Use a bilevel alpha mask | |
Perform single-color antialiasing (using shades of gray for black text on a white background, for example). | |
Perform antialiasing by taking advantage of the order of subpixel elements on devices such as LCD panels |
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()
.
|
a cairo_t |
|
the new antialiasing mode |
cairo_antialias_t cairo_get_antialias (cairo_t *cr);
Gets the current shape antialiasing mode, as set by cairo_set_shape_antialias()
.
|
a cairo context |
Returns : |
the current shape antialiasing mode. |
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
cr
will be put into an error state with a status of
#CAIRO_STATUS_INVALID_DASH
.
|
a cairo context |
|
an array specifying alternate lengths of on and off stroke portions |
|
the length of the dashes array |
|
an offset into the dash pattern at which the stroke should start |
int cairo_get_dash_count (cairo_t *cr);
This function returns the length of the dash array in cr
(0 if dashing
is not currently in effect).
See also cairo_set_dash()
and cairo_get_dash()
.
|
a cairo_t |
Returns : |
the length of the dash array, or 0 if no dash array set. |
Since 1.4
void cairo_get_dash (cairo_t *cr, double *dashes, double *offset);
Gets the current dash array. If not NULL
, dashes
should be big
enough to hold at least the number of values returned by
cairo_get_dash_count()
.
|
a cairo_t |
|
return value for the dash array, or NULL
|
|
return value for the current dash offset, or NULL
|
Since 1.4
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.)
The default fill rule is CAIRO_FILL_RULE_WINDING
.
New entries may be added in future versions.
If the path crosses the ray from left-to-right, counts +1. If the path crosses the ray from right to left, counts -1. (Left and right are determined from the perspective of looking along the ray from the starting point.) If the total count is non-zero, the point will be filled. | |
Counts the total number of intersections, without regard to the orientation of the contour. If the total number of intersections is odd, the point will be filled. |
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.
The default fill rule is CAIRO_FILL_RULE_WINDING
.
|
a cairo_t |
|
a fill rule, specified as a cairo_fill_rule_t |
cairo_fill_rule_t cairo_get_fill_rule (cairo_t *cr);
Gets the current fill rule, as set by cairo_set_fill_rule()
.
|
a cairo context |
Returns : |
the current fill rule. |
typedef enum _cairo_line_cap { CAIRO_LINE_CAP_BUTT, CAIRO_LINE_CAP_ROUND, CAIRO_LINE_CAP_SQUARE } cairo_line_cap_t;
Specifies how to render the endpoints of the path when stroking.
The default line cap style is CAIRO_LINE_CAP_BUTT
.
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.
The default line cap style is CAIRO_LINE_CAP_BUTT
.
|
a cairo context |
|
a line cap style |
cairo_line_cap_t cairo_get_line_cap (cairo_t *cr);
Gets the current line cap style, as set by cairo_set_line_cap()
.
|
a cairo context |
Returns : |
the current line cap style. |
typedef enum _cairo_line_join { CAIRO_LINE_JOIN_MITER, CAIRO_LINE_JOIN_ROUND, CAIRO_LINE_JOIN_BEVEL } cairo_line_join_t;
Specifies how to render the junction of two lines when stroking.
The default line join style is CAIRO_LINE_JOIN_MITER
.
use a sharp (angled) corner, see
cairo_set_miter_limit()
|
|
use a rounded join, the center of the circle is the joint point | |
use a cut-off join, the join is cut off at half the line width from the joint point |
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.
The default line join style is CAIRO_LINE_JOIN_MITER
.
|
a cairo context |
|
a line join style |
cairo_line_join_t cairo_get_line_join (cairo_t *cr);
Gets the current line join style, as set by cairo_set_line_join()
.
|
a cairo context |
Returns : |
the current line join style. |
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.
|
a cairo_t |
|
a line width |
double cairo_get_line_width (cairo_t *cr);
This function returns the current line width value exactly as set by
cairo_set_line_width()
. Note that the value is unchanged even if
the CTM has changed between the calls to cairo_set_line_width()
and
cairo_get_line_width()
.
|
a cairo context |
Returns : |
the current line width. |
void cairo_set_miter_limit (cairo_t *cr, 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 cairo_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 cairo_stroke()
, cairo_stroke_extents()
, and
cairo_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)
|
a cairo context |
|
miter limit to set |
double cairo_get_miter_limit (cairo_t *cr);
Gets the current miter limit, as set by cairo_set_miter_limit()
.
|
a cairo context |
Returns : |
the current miter limit. |
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_operator_t is used to set the compositing operator for all cairo drawing operations.
The default operator is CAIRO_OPERATOR_OVER
.
The operators marked as unbounded modify their destination even outside of the mask layer (that is, their effect is not bound by the mask layer). However, their effect can still be limited by way of clipping.
To keep things simple, the operator descriptions here document the behavior for when both source and destination are either fully transparent or fully opaque. The actual implementation works for translucent layers too. For a more detailed explanation of the effects of each operator, including the mathematical definitions, see http://cairographics.org/operators/.
clear destination layer (bounded) | |
replace destination layer (bounded) | |
draw source layer on top of destination layer (bounded) | |
draw source where there was destination content (unbounded) | |
draw source where there was no destination content (unbounded) | |
draw source on top of destination content and only there | |
ignore the source | |
draw destination on top of source | |
leave destination only where there was source content (unbounded) | |
leave destination only where there was no source content | |
leave destination on top of source content and only there (unbounded) | |
source and destination are shown where there is only one of them | |
source and destination layers are accumulated | |
like over, but assuming source and dest are disjoint geometries |
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.
The default operator is CAIRO_OPERATOR_OVER
.
|
a cairo_t |
|
a compositing operator, specified as a cairo_operator_t |
cairo_operator_t cairo_get_operator (cairo_t *cr);
Gets the current compositing operator for a cairo context.
|
a cairo context |
Returns : |
the current compositing operator. |
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.)
|
a cairo_t |
|
the tolerance, in device units (typically pixels) |
double cairo_get_tolerance (cairo_t *cr);
Gets the current tolerance value, as set by cairo_set_tolerance()
.
|
a cairo context |
Returns : |
the current tolerance value. |
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()
.
|
a cairo context |
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()
.
|
a cairo context |
void cairo_clip_extents (cairo_t *cr, double *x1, double *y1, double *x2, double *y2);
Computes a bounding box in user coordinates covering the area inside the current clip.
|
a cairo context |
|
left of the resulting extents |
|
top of the resulting extents |
|
right of the resulting extents |
|
bottom of the resulting extents |
Since 1.4
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.
|
a cairo context |
typedef struct { double x, y, width, height; } cairo_rectangle_t;
A data structure for holding a rectangle.
double |
X coordinate of the left side of the rectangle |
double |
Y coordinate of the the top side of the rectangle |
double |
width of the rectangle |
double |
height of the rectangle |
Since 1.4
typedef struct { cairo_status_t status; cairo_rectangle_t *rectangles; int num_rectangles; } cairo_rectangle_list_t;
A data structure for holding a dynamically allocated array of rectangles.
cairo_status_t |
Error status of the rectangle list |
cairo_rectangle_t * |
Array containing the rectangles |
int |
Number of rectangles in this list |
Since 1.4
void cairo_rectangle_list_destroy (cairo_rectangle_list_t *rectangle_list);
Unconditionally frees rectangle_list
and all associated
references. After this call, the rectangle_list
pointer must not
be dereferenced.
|
a rectangle list, as obtained from cairo_copy_clip_rectangles()
|
Since 1.4
cairo_rectangle_list_t * cairo_copy_clip_rectangle_list (cairo_t *cr);
Gets the current clip region as a list of rectangles in user coordinates.
Never returns NULL
.
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.
|
a cairo context |
Returns : |
the current clip region as a list of rectangles in user coordinates,
which should be destroyed using cairo_rectangle_list_destroy() .
|
Since 1.4
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()
.
|
a cairo context |
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()
.
|
a cairo context |
void cairo_fill_extents (cairo_t *cr, double *x1, double *y1, double *x2, double *y2);
Computes a bounding box in user coordinates covering the area that
would be affected, (the "inked" area), by a cairo_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 cairo_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 cairo_fill_extents()
must necessarily do more work to
compute the precise inked areas in light of the fill rule, so
cairo_path_extents()
may be more desirable for sake of performance
if the non-inked path extents are desired.
See cairo_fill()
, cairo_set_fill_rule()
and cairo_fill_preserve()
.
|
a cairo context |
|
left of the resulting extents |
|
top of the resulting extents |
|
right of the resulting extents |
|
bottom of the resulting extents |
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
affected by a cairo_fill()
operation given the current path and
filling parameters. Surface dimensions and clipping are not taken
into account.
See cairo_fill()
, cairo_set_fill_rule()
and cairo_fill_preserve()
.
|
a cairo context |
|
X coordinate of the point to test |
|
Y coordinate of the point to test |
Returns : |
A non-zero value if the point is inside, or zero if outside. |
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.)
|
a cairo context |
|
a cairo_pattern_t |
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.)
|
a cairo context |
|
a cairo_surface_t |
|
X coordinate at which to place the origin of surface
|
|
Y coordinate at which to place the origin of surface
|
void cairo_paint (cairo_t *cr);
A drawing operator that paints the current source everywhere within the current clip region.
|
a cairo context |
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.
|
a cairo context |
|
alpha value, between 0 (transparent) and 1 (opaque) |
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.
|
a cairo context |
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()
.
|
a cairo context |
void cairo_stroke_extents (cairo_t *cr, double *x1, double *y1, double *x2, double *y2);
Computes a bounding box in user coordinates covering the area that
would be affected, (the "inked" area), by a cairo_stroke()
operation 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
cairo_stroke_extents()
will return an empty rectangle. Contrast with
cairo_path_extents()
which can be used to compute the non-empty
bounds as the line width approaches zero.
Note that cairo_stroke_extents()
must necessarily do more work to
compute the precise inked areas in light of the stroke parameters,
so cairo_path_extents()
may be more desirable for sake of
performance if non-inked path extents are desired.
See cairo_stroke()
, cairo_set_line_width()
, cairo_set_line_join()
,
cairo_set_line_cap()
, cairo_set_dash()
, and
cairo_stroke_preserve()
.
|
a cairo context |
|
left of the resulting extents |
|
top of the resulting extents |
|
right of the resulting extents |
|
bottom of the resulting extents |
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
affected by a cairo_stroke()
operation given the current path and
stroking parameters. Surface dimensions and clipping are not taken
into account.
See cairo_stroke()
, cairo_set_line_width()
, cairo_set_line_join()
,
cairo_set_line_cap()
, cairo_set_dash()
, and
cairo_stroke_preserve()
.
|
a cairo context |
|
X coordinate of the point to test |
|
Y coordinate of the point to test |
Returns : |
A non-zero value if the point is inside, or zero if outside. |
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.
This is a convenience function that simply calls
cairo_surface_copy_page()
on cr
's target.
|
a cairo context |
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.
This is a convenience function that simply calls
cairo_surface_show_page()
on cr
's target.
|
a cairo context |
unsigned int cairo_get_reference_count (cairo_t *cr);
Returns the current reference count of cr
.
|
a cairo_t |
Returns : |
the current reference count of cr . If the
object is a nil object, 0 will be returned.
|
Since 1.4
cairo_status_t cairo_set_user_data (cairo_t *cr, const cairo_user_data_key_t *key, void *user_data, cairo_destroy_func_t destroy);
Attach user data to cr
. To remove user data from a surface,
call this function with the key that was used to set it and NULL
for data
.
|
a cairo_t |
|
the address of a cairo_user_data_key_t to attach the user data to |
|
the user data to attach to the cairo_t |
|
a cairo_destroy_func_t which will be called when the cairo_t is destroyed or when new user data is attached using the same key. |
Returns : |
CAIRO_STATUS_SUCCESS or CAIRO_STATUS_NO_MEMORY if a
slot could not be allocated for the user data.
|
Since 1.4
void * cairo_get_user_data (cairo_t *cr, const cairo_user_data_key_t *key);
Return user data previously attached to cr
using the specified
key. If no user data has been attached with the given key this
function returns NULL
.
|
a cairo_t |
|
the address of the cairo_user_data_key_t the user data was attached to |
Returns : |
the user data previously attached or NULL .
|
Since 1.4