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.

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.

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,
                                                         GdkPixbufAlphaMode alpha_mode,
                                                         int alpha_threshold,
                                                         GdkRgbDither dither,
                                                         int x_dither,
                                                         int y_dither);

Renders a rectangular portion of a pixbuf to a drawable. The destination drawable must have a colormap. All windows have a colormap, however, pixmaps only have colormap by default if they were created with a non-NULL window argument. Otherwise a colormap must be set on them with gdk_drawable_set_colormap.

On older X servers, rendering pixbufs with an alpha channel involves round trips to the X server, and may be somewhat slow.

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 thresholded 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_draw_pixbuf() and gdk_pixbuf_render_threshold_alpha().

The pixmap that is created is created for the colormap returned by gdk_rgb_get_colormap(). You normally will want to instead use the actual colormap for a widget, and use gdk_pixbuf_render_pixmap_and_mask_for_colormap().

If the pixbuf does not have an alpha channel, then *mask_return will be set to NULL.

gdk_pixbuf_render_pixmap_and_mask_for_colormap ()

void                gdk_pixbuf_render_pixmap_and_mask_for_colormap
                                                        (GdkPixbuf *pixbuf,
                                                         GdkColormap *colormap,
                                                         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_draw_pixbuf(), and gdk_pixbuf_render_threshold_alpha().

The pixmap that is created uses the GdkColormap specified by colormap. This colormap must match the colormap of the window where the pixmap will eventually be used or an error will result.

If the pixbuf does not have an alpha channel, then *mask_return will be set to NULL.

gdk_pixbuf_get_from_drawable ()

GdkPixbuf*          gdk_pixbuf_get_from_drawable        (GdkPixbuf *dest,
                                                         GdkDrawable *src,
                                                         GdkColormap *cmap,
                                                         int src_x,
                                                         int src_y,
                                                         int dest_x,
                                                         int dest_y,
                                                         int width,
                                                         int height);

Transfers image data from a GdkDrawable and converts it to an RGB(A) representation inside a GdkPixbuf. In other words, copies image data from a server-side drawable to a client-side RGB(A) buffer. This allows you to efficiently read individual pixels on the client side.

If the drawable src has no colormap (gdk_drawable_get_colormap() returns NULL), then a suitable colormap must be specified. Typically a GdkWindow or a pixmap created by passing a GdkWindow to gdk_pixmap_new() will already have a colormap associated with it. If the drawable has a colormap, the cmap argument will be ignored. If the drawable is a bitmap (1 bit per pixel pixmap), then a colormap is not required; pixels with a value of 1 are assumed to be white, and pixels with a value of 0 are assumed to be black. For taking screenshots, gdk_colormap_get_system() returns the correct colormap to use.

If the specified destination pixbuf dest is NULL, then this function will create an RGB pixbuf with 8 bits per channel and no alpha, with the same size specified by the width and height arguments. In this case, the dest_x and dest_y arguments must be specified as 0. If the specified destination pixbuf is not NULL and it contains alpha information, then the filled pixels will be set to full opacity (alpha = 255).

If the specified drawable is a pixmap, then the requested source rectangle must be completely contained within the pixmap, otherwise the function will return NULL. For pixmaps only (not for windows) passing -1 for width or height is allowed to mean the full width or height of the pixmap.

If the specified drawable is a window, and the window is off the screen, then there is no image data in the obscured/offscreen regions to be placed in the pixbuf. The contents of portions of the pixbuf corresponding to the offscreen region are undefined.

If the window you're obtaining data from is partially obscured by other windows, then the contents of the pixbuf areas corresponding to the obscured regions are undefined.

If the target drawable is not mapped (typically because it's iconified/minimized or not on the current workspace), then NULL will be returned.

If memory can't be allocated for the return value, NULL will be returned instead.

(In short, there are several ways this function can fail, and if it fails it returns NULL; so check the return value.)

This function calls gdk_drawable_get_image() internally and converts the resulting image to a GdkPixbuf, so the documentation for gdk_drawable_get_image() may also be relevant.

gdk_pixbuf_get_from_image ()

GdkPixbuf*          gdk_pixbuf_get_from_image           (GdkPixbuf *dest,
                                                         GdkImage *src,
                                                         GdkColormap *cmap,
                                                         int src_x,
                                                         int src_y,
                                                         int dest_x,
                                                         int dest_y,
                                                         int width,
                                                         int height);

Same as gdk_pixbuf_get_from_drawable() but gets the pixbuf from an image.