GdkRGB

## GdkRGB GdkRGB — Renders RGB, grayscale, or indexed image data to a GdkDrawable |

## Includes

    #include <gdk/gdk.h>

## Description

GdkRGB is a low-level module which renders RGB, grayscale, and indexed colormap images to a GdkDrawable. It does this as efficiently as possible, handling issues such as colormaps, visuals, dithering, temporary buffers, and so on. Most code should use the higher-level GdkPixbuf features in place of this module; for example, `gdk_draw_pixbuf()` uses GdkRGB in its implementation.

GdkRGB allocates a color cube to use when rendering images. You can set the threshold for installing colormaps with `gdk_rgb_set_min_colors()`. The default is 5x5x5 (125). If a colorcube of this size or larger can be allocated in the default colormap, then that's done. Otherwise, GdkRGB creates its own private colormap. Setting it to 0 means that it always tries to use the default colormap, and setting it to 216 means that it always creates a private one if it cannot allocate the 6x6x6 colormap in the default. If you always want a private colormap (to avoid consuming too many colormap entries for other apps, say), you can use `gdk_rgb_set_install(TRUE)`. Setting the value greater than 216 exercises a bug in older versions of GdkRGB. Note, however, that setting it to 0 doesn't let you get away with ignoring the colormap and visual - a colormap is always created in grayscale and direct color modes, and the visual is changed in cases where a "better" visual than the default is available.

If GDK is built with the Sun mediaLib library, the GdkRGB functions are accelerated using mediaLib, which provides hardware acceleration on Intel, AMD, and Sparc chipsets. If desired, mediaLib support can be turned off by setting the GDK_DISABLE_MEDIALIB environment variable.

Example 3. A simple example program using GdkRGB

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    #include <gtk/gtk.h>
    #define IMAGE_WIDTH 256
    #define IMAGE_HEIGHT    256
    guchar rgbbuf[IMAGE_WIDTH * IMAGE_HEIGHT * 3];
    gboolean on_darea_expose (GtkWidget *widget,
                  GdkEventExpose *event,
                  gpointer user_data);
    int
    main (int argc, char *argv[])
    {
      GtkWidget *window, *darea;
      gint x, y;
      guchar *pos;
      gtk_init (&argc, &argv);
      window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
      darea = gtk_drawing_area_new ();
      gtk_widget_set_size_request (darea, IMAGE_WIDTH, IMAGE_HEIGHT);
      gtk_container_add (GTK_CONTAINER (window), darea);
      gtk_signal_connect (GTK_OBJECT (darea), "expose-event",
                          GTK_SIGNAL_FUNC (on_darea_expose), NULL);
      gtk_widget_show_all (window);
      /* Set up the RGB buffer. */
      pos = rgbbuf;
      for (y = 0; y < IMAGE_HEIGHT; y++)
        {
          for (x = 0; x < IMAGE_WIDTH; x++)
        {
          *pos++ = x - x % 32;          /* Red. */
          *pos++ = (x / 32) * 4 + y - y % 32;   /* Green. */
          *pos++ = y - y % 32;          /* Blue. */
        }
        }
      gtk_main ();
      return 0;
    }
    gboolean
    on_darea_expose (GtkWidget *widget,
             GdkEventExpose *event,
             gpointer user_data)
    {
      gdk_draw_rgb_image (widget->window, widget->style->fg_gc[GTK_STATE_NORMAL],
                  0, 0, IMAGE_WIDTH, IMAGE_HEIGHT,
                  GDK_RGB_DITHER_MAX, rgbbuf, IMAGE_WIDTH * 3);
      return TRUE;
    }

## Functions

## Types and Values

## See Also

GdkColor | The underlying GDK mechanism for allocating colors.
GdkPixbuf and `gdk_draw_pixbuf()` | Higher-level image handling.