Xlib Rendering
3
GDK-PIXBUF Library

# Xlib Rendering

Rendering a pixbuf to an X drawable.

## Synopsis

    #include <gdk-pixbuf/gdk-pixbuf.h>

    void                gdk_pixbuf_xlib_render_threshold_alpha
                                                            (GdkPixbuf *pixbuf,
                                                             Pixmap bitmap,
                                                             int src_x,
                                                             int src_y,
                                                             int dest_x,
                                                             int dest_y,
                                                             int width,
                                                             int height,
                                                             int alpha_threshold);
    void                gdk_pixbuf_xlib_render_to_drawable  (GdkPixbuf *pixbuf,
                                                             Drawable drawable,
                                                             GC gc,
                                                             int src_x,
                                                             int src_y,
                                                             int dest_x,
                                                             int dest_y,
                                                             int width,
                                                             int height,
                                                             XlibRgbDither dither,
                                                             int x_dither,
                                                             int y_dither);
    void                gdk_pixbuf_xlib_render_to_drawable_alpha
                                                            (GdkPixbuf *pixbuf,
                                                             Drawable drawable,
                                                             int src_x,
                                                             int src_y,
                                                             int dest_x,
                                                             int dest_y,
                                                             int width,
                                                             int height,
                                                             GdkPixbufAlphaMode alpha_mode,
                                                             int alpha_threshold,
                                                             XlibRgbDither dither,
                                                             int x_dither,
                                                             int y_dither);
    void                gdk_pixbuf_xlib_render_pixmap_and_mask
                                                            (GdkPixbuf *pixbuf,
                                                             Pixmap *pixmap_return,
                                                             Pixmap *mask_return,
                                                             int alpha_threshold);

## Description

The &gdk-pixbuf; Xlib library provides several convenience functions to render pixbufs to X drawables. It uses XlibRGB to render the image data.

These functions are analogous to those for the GDK version of &gdk-pixbuf;.

## Details

### gdk_pixbuf_xlib_render_threshold_alpha ()

    void                gdk_pixbuf_xlib_render_threshold_alpha
                                                            (GdkPixbuf *pixbuf,
                                                             Pixmap 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_xlib_render_to_drawable ()

    void                gdk_pixbuf_xlib_render_to_drawable  (GdkPixbuf *pixbuf,
                                                             Drawable drawable,
                                                             GC gc,
                                                             int src_x,
                                                             int src_y,
                                                             int dest_x,
                                                             int dest_y,
                                                             int width,
                                                             int height,
                                                             XlibRgbDither 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 XlibRGB, so the specified drawable must have the XlibRGB 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 XlibRGB 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 XlibRGB.

`x_dither` :

  X offset for dither.

`y_dither` :

  Y offset for dither.

### gdk_pixbuf_xlib_render_to_drawable_alpha ()

    void                gdk_pixbuf_xlib_render_to_drawable_alpha
                                                            (GdkPixbuf *pixbuf,
                                                             Drawable drawable,
                                                             int src_x,
                                                             int src_y,
                                                             int dest_x,
                                                             int dest_y,
                                                             int width,
                                                             int height,
                                                             GdkPixbufAlphaMode alpha_mode,
                                                             int alpha_threshold,
                                                             XlibRgbDither dither,
                                                             int x_dither,
                                                             int y_dither);

Renders a rectangular portion of a pixbuf to a drawable. This is done using XlibRGB, so the specified drawable must have the XlibRGB 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_xlib_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 XlibRGB.

`x_dither` :

  X offset for dither.

`y_dither` :

  Y offset for dither.

### gdk_pixbuf_xlib_render_pixmap_and_mask ()

    void                gdk_pixbuf_xlib_render_pixmap_and_mask
                                                            (GdkPixbuf *pixbuf,
                                                             Pixmap *pixmap_return,
                                                             Pixmap *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_xlib_render_to_drawable_alpha()` or `gdk_pixbuf_xlib_render_to_drawable()`, and `gdk_pixbuf_xlib_render_threshold_alpha()`.

If the pixbuf does not have an alpha channel, then *`mask_return` will be set to None.

`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.