Cairo Interaction

Cairo Interaction — Functions to support using cairo

Includes

#include <gdk/gdk.h>

Description

Cairo is a graphics library that supports vector graphics and image compositing that can be used with GDK. GTK+ does all of its drawing using cairo.

GDK does not wrap the cairo API, instead it allows to create cairo contexts which can be used to draw on GdkSurfaces. Additional functions allow use GdkRectangles with cairo and to use GdkRGBAs, GdkPixbufs and GdkSurfaces as sources for drawing operations.

Functions

gdk_surface_create_similar_surface ()

cairo_surface_t *
gdk_surface_create_similar_surface (GdkSurface *surface,
                                    cairo_content_t content,
                                    int width,
                                    int height);

Create a new surface that is as compatible as possible with the given surface . For example the new surface will have the same fallback resolution and font options as surface . Generally, the new surface will also use the same backend as surface , unless that is not possible for some reason. The type of the returned surface may be examined with cairo_surface_get_type().

Initially the surface contents are all 0 (transparent if contents have transparency, black otherwise.)

Parameters

surface

surface to make new surface similar to

 

content

the content for the new surface

 

width

width of the new surface

 

height

height of the new surface

 

Returns

a pointer to the newly allocated surface. The caller owns the surface and should call cairo_surface_destroy() when done with it.

This function always returns a valid pointer, but it will return a pointer to a “nil” surface if other is already in an error state or any other error occurs.


gdk_cairo_get_clip_rectangle ()

gboolean
gdk_cairo_get_clip_rectangle (cairo_t *cr,
                              GdkRectangle *rect);

This is a convenience function around cairo_clip_extents(). It rounds the clip extents to integer coordinates and returns a boolean indicating if a clip area exists.

Parameters

cr

a cairo context

 

rect

return location for the clip, or NULL.

[out][allow-none]

Returns

TRUE if a clip rectangle exists, FALSE if all of cr is clipped and all drawing can be skipped


gdk_cairo_set_source_rgba ()

void
gdk_cairo_set_source_rgba (cairo_t *cr,
                           const GdkRGBA *rgba);

Sets the specified GdkRGBA as the source color of cr .

Parameters

cr

a cairo context

 

rgba

a GdkRGBA

 

gdk_cairo_set_source_pixbuf ()

void
gdk_cairo_set_source_pixbuf (cairo_t *cr,
                             const GdkPixbuf *pixbuf,
                             gdouble pixbuf_x,
                             gdouble pixbuf_y);

Sets the given pixbuf as the source pattern for cr .

The pattern has an extend mode of CAIRO_EXTEND_NONE and is aligned so that the origin of pixbuf is pixbuf_x , pixbuf_y .

Parameters

cr

a cairo context

 

pixbuf

a GdkPixbuf

 

pixbuf_x

X coordinate of location to place upper left corner of pixbuf

 

pixbuf_y

Y coordinate of location to place upper left corner of pixbuf

 

gdk_cairo_rectangle ()

void
gdk_cairo_rectangle (cairo_t *cr,
                     const GdkRectangle *rectangle);

Adds the given rectangle to the current path of cr .

Parameters

cr

a cairo context

 

rectangle

a GdkRectangle

 

gdk_cairo_region ()

void
gdk_cairo_region (cairo_t *cr,
                  const cairo_region_t *region);

Adds the given region to the current path of cr .

Parameters

cr

a cairo context

 

region

a cairo_region_t

 

gdk_cairo_region_create_from_surface ()

cairo_region_t *
gdk_cairo_region_create_from_surface (cairo_surface_t *surface);

Creates region that describes covers the area where the given surface is more than 50% opaque.

This function takes into account device offsets that might be set with cairo_surface_set_device_offset().

Parameters

surface

a cairo surface

 

Returns

A cairo_region_t; must be freed with cairo_region_destroy()


gdk_cairo_draw_from_gl ()

void
gdk_cairo_draw_from_gl (cairo_t *cr,
                        GdkSurface *surface,
                        int source,
                        int source_type,
                        int buffer_scale,
                        int x,
                        int y,
                        int width,
                        int height);

This is the main way to draw GL content in GTK+. It takes a render buffer ID (source_type == GL_RENDERBUFFER) or a texture id (source_type == GL_TEXTURE) and draws it onto cr with an OVER operation, respecting the current clip. The top left corner of the rectangle specified by x , y , width and height will be drawn at the current (0,0) position of the cairo_t.

This will work for *all* cairo_t, as long as surface is realized, but the fallback implementation that reads back the pixels from the buffer may be used in the general case. In the case of direct drawing to a surface with no special effects applied to cr it will however use a more efficient approach.

For GL_RENDERBUFFER the code will always fall back to software for buffers with alpha components, so make sure you use GL_TEXTURE if using alpha.

Calling this may change the current GL context.

Parameters

cr

a cairo context

 

surface

The surface we're rendering for (not necessarily into)

 

source

The GL ID of the source buffer

 

source_type

The type of the source

 

buffer_scale

The scale-factor that the source buffer is allocated for

 

x

The source x position in source to start copying from in GL coordinates

 

y

The source y position in source to start copying from in GL coordinates

 

width

The width of the region to draw

 

height

The height of the region to draw

 

gdk_cairo_surface_upload_to_gl ()

void
gdk_cairo_surface_upload_to_gl (cairo_surface_t *surface,
                                int target,
                                int width,
                                int height,
                                GdkGLContext *context);

Uploads the contents of a Cairo surface to a GL texture target .

Parameters

surface

a Cairo surface

 

target

a GL texture target

 

width

the width of the texture target

 

height

the height of the texture target

 

context

a GdkGLContext, or NULL to use the currently bound context.

[nullable]

Types and Values