The
gdk-pixbuf
Library
gdk-pixbuf-creating.html
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Rendering
Name
Rendering -- Rendering a pixbuf to a GDK drawable.
Synopsis
#include <gdk-pixbuf/gdk-pixbuf.h>
enum
gdk-pixbuf-rendering.html#GDKPIXBUFALPHAMODE
GdkPixbufAlphaMode
;
void
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-TO-DRAWABLE-ALPHA
gdk_pixbuf_render_to_drawable_alpha
(GdkPixbuf *pixbuf,
GdkDrawable *drawable,
int src_x,
int src_y,
int dest_x,
int dest_y,
int width,
int height,
gdk-pixbuf-rendering.html#GDKPIXBUFALPHAMODE
GdkPixbufAlphaMode
alpha_mode,
int alpha_threshold,
GdkRgbDither dither,
int x_dither,
int y_dither);
void
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-TO-DRAWABLE
gdk_pixbuf_render_to_drawable
(GdkPixbuf *pixbuf,
GdkDrawable *drawable,
GdkGC *gc,
int src_x,
int src_y,
int dest_x,
int dest_y,
int width,
int height,
GdkRgbDither dither,
int x_dither,
int y_dither);
void
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-THRESHOLD-ALPHA
gdk_pixbuf_render_threshold_alpha
(GdkPixbuf *pixbuf,
GdkBitmap *bitmap,
int src_x,
int src_y,
int dest_x,
int dest_y,
int width,
int height,
int alpha_threshold);
void
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-PIXMAP-AND-MASK
gdk_pixbuf_render_pixmap_and_mask
(GdkPixbuf *pixbuf,
GdkPixmap **pixmap_return,
GdkBitmap **mask_return,
int alpha_threshold);
Description
The
gdk-pixbuf
library provides several convenience functions to
render pixbufs to GDK drawables.  It uses the GdkRGB to render the
image data.
At this point there is not a standard alpha channel extension for
the X Window System, so it is not possible to use full opacity
information when painting images to arbitrary drawables.  The
gdk-pixbuf
convenience functions will threshold the opacity
information to create a bi-level clipping mask (black and white),
and use that to draw the image onto a drawable.
Important:
Since these functions use GdkRGB for rendering, you must
initialize GdkRGB before using any of them.  You can do this by
calling gdk_rgb_init() near the beginning of your program.
Details
enum GdkPixbufAlphaMode
typedef enum {
GDK_PIXBUF_ALPHA_BILEVEL,
GDK_PIXBUF_ALPHA_FULL
} GdkPixbufAlphaMode;
These values can be passed to
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-TO-DRAWABLE-ALPHA
gdk_pixbuf_render_to_drawable_alpha
() to control how the alpha
chanel of an image should be handled.  This function can create a
bilevel clipping mask (black and white) and use it while painting
the image.  In the future, when the X Window System gets an alpha
channel extension, it will be possible to do full alpha
compositing onto arbitrary drawables.  For now both cases fall
back to a bilevel clipping mask.
GDK_PIXBUF_ALPHA_BILEVEL
A bilevel clipping mask (black and white)
will be created and used to draw the image.  Pixels below 0.5 opacity
will be considered fully transparent, and all others will be
considered fully opaque.
GDK_PIXBUF_ALPHA_FULL
For now falls back to GDK_PIXBUF_ALPHA_BILEVEL.
In the future it will do full alpha compositing.
gdk_pixbuf_render_to_drawable_alpha ()
void        gdk_pixbuf_render_to_drawable_alpha
(GdkPixbuf *pixbuf,
GdkDrawable *drawable,
int src_x,
int src_y,
int dest_x,
int dest_y,
int width,
int height,
gdk-pixbuf-rendering.html#GDKPIXBUFALPHAMODE
GdkPixbufAlphaMode
alpha_mode,
int alpha_threshold,
GdkRgbDither dither,
int x_dither,
int y_dither);
Renders a rectangular portion of a pixbuf to a drawable.  This is done using
GdkRGB, so the specified drawable must have the GdkRGB visual and colormap.
When used with GDK_PIXBUF_ALPHA_BILEVEL, this function has to create a bitmap
out of the thresholded alpha channel of the image and, it has to set this
bitmap as the clipping mask for the GC used for drawing.  This can be a
significant performance penalty depending on the size and the complexity of
the alpha channel of the image.  If performance is crucial, consider handling
the alpha channel yourself (possibly by caching it in your application) and
using
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-TO-DRAWABLE
gdk_pixbuf_render_to_drawable
() or GdkRGB directly instead.
pixbuf
:
A pixbuf.
drawable
:
Destination drawable.
src_x
:
Source X coordinate within pixbuf.
src_y
:
Source Y coordinates within pixbuf.
dest_x
:
Destination X coordinate within drawable.
dest_y
:
Destination Y coordinate within drawable.
width
:
Width of region to render, in pixels.
height
:
Height of region to render, in pixels.
alpha_mode
:
If the image does not have opacity information, this is ignored.
Otherwise, specifies how to handle transparency when rendering.
alpha_threshold
:
If the image does have opacity information and
alpha_mode
is GDK_PIXBUF_ALPHA_BILEVEL, specifies the threshold value for opacity
values.
dither
:
Dithering mode for GdkRGB.
x_dither
:
X offset for dither.
y_dither
:
Y offset for dither.
gdk_pixbuf_render_to_drawable ()
void        gdk_pixbuf_render_to_drawable   (GdkPixbuf *pixbuf,
GdkDrawable *drawable,
GdkGC *gc,
int src_x,
int src_y,
int dest_x,
int dest_y,
int width,
int height,
GdkRgbDither dither,
int x_dither,
int y_dither);
Renders a rectangular portion of a pixbuf to a drawable while using the
specified GC.  This is done using GdkRGB, so the specified drawable must have
the GdkRGB visual and colormap.  Note that this function will ignore the
opacity information for images with an alpha channel; the GC must already
have the clipping mask set if you want transparent regions to show through.
For an explanation of dither offsets, see the GdkRGB documentation.  In
brief, the dither offset is important when re-rendering partial regions of an
image to a rendered version of the full image, or for when the offsets to a
base position change, as in scrolling.  The dither matrix has to be shifted
for consistent visual results.  If you do not have any of these cases, the
dither offsets can be both zero.
pixbuf
:
A pixbuf.
drawable
:
Destination drawable.
gc
:
GC used for rendering.
src_x
:
Source X coordinate within pixbuf.
src_y
:
Source Y coordinate within pixbuf.
dest_x
:
Destination X coordinate within drawable.
dest_y
:
Destination Y coordinate within drawable.
width
:
Width of region to render, in pixels.
height
:
Height of region to render, in pixels.
dither
:
Dithering mode for GdkRGB.
x_dither
:
X offset for dither.
y_dither
:
Y offset for dither.
gdk_pixbuf_render_threshold_alpha ()
void        gdk_pixbuf_render_threshold_alpha
(GdkPixbuf *pixbuf,
GdkBitmap *bitmap,
int src_x,
int src_y,
int dest_x,
int dest_y,
int width,
int height,
int alpha_threshold);
Takes the opacity values in a rectangular portion of a pixbuf and thresholds
them to produce a bi-level alpha mask that can be used as a clipping mask for
a drawable.
pixbuf
:
A pixbuf.
bitmap
:
Bitmap where the bilevel mask will be painted to.
src_x
:
Source X coordinate.
src_y
:
source Y coordinate.
dest_x
:
Destination X coordinate.
dest_y
:
Destination Y coordinate.
width
:
Width of region to threshold.
height
:
Height of region to threshold.
alpha_threshold
:
Opacity values below this will be painted as zero; all
other values will be painted as one.
gdk_pixbuf_render_pixmap_and_mask ()
void        gdk_pixbuf_render_pixmap_and_mask
(GdkPixbuf *pixbuf,
GdkPixmap **pixmap_return,
GdkBitmap **mask_return,
int alpha_threshold);
Creates a pixmap and a mask bitmap which are returned in the
pixmap_return
and
mask_return
arguments, respectively, and renders a pixbuf and its
corresponding tresholded alpha mask to them.  This is merely a convenience
function; applications that need to render pixbufs with dither offsets or to
given drawables should use
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-TO-DRAWABLE-ALPHA
gdk_pixbuf_render_to_drawable_alpha
() or
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-TO-DRAWABLE
gdk_pixbuf_render_to_drawable
(), and
gdk-pixbuf-rendering.html#GDK-PIXBUF-RENDER-THRESHOLD-ALPHA
gdk_pixbuf_render_threshold_alpha
().
If the pixbuf does not have an alpha channel, then *
mask_return
will be set
to
NULL
.
pixbuf
:
A pixbuf.
pixmap_return
:
Return value for the created pixmap.
mask_return
:
Return value for the created mask.
alpha_threshold
:
Threshold value for opacity values.
See Also
GdkRGB
gdk-pixbuf-creating.html
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Image Data in Memory
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