GdkRGB

gdk_rgb_init ()

void        gdk_rgb_init                    (void);

Initializes GdkRgb statically. It may be called more than once with no ill effects. It must, however, be called before any other GdkRgb operations are performed.

The GdkRgb "context" is allocated statically. Thus, GdkRgb may be used to drive only one visual in any given application. GdkRgb automatically selects a best visual and sets its own colormap, if necessary. gdk_rgb_get_visual() and gdk_rgb_get_cmap() retrieve the chosen visual and colormap, respectively.

gdk_draw_rgb_image ()

void        gdk_draw_rgb_image              (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *rgb_buf,
                                             gint rowstride);

Draws an RGB image in the drawable. This is the core GdkRgb function, and likely the only one you will need to use other than the initialization stuff.

The rowstride parameter allows for lines to be aligned more flexibly. For example, lines may be allocated to begin on 32-bit boundaries, even if the width of the rectangle is odd. Rowstride is also useful when drawing a subrectangle of a larger image in memory. Finally, to replicate the same line a number of times, the trick of setting rowstride to 0 is allowed.

In general, for 0 <= i < width and 0 <= j < height, the pixel (x + i, y + j) is colored with red value rgb_buf[j * rowstride + i * 3], green value rgb_buf[j * rowstride + i * 3 + 1], and blue value rgb_buf[j * rowstride + i * 3 + 2].

gdk_draw_rgb_image_dithalign ()

void        gdk_draw_rgb_image_dithalign    (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *rgb_buf,
                                             gint rowstride,
                                             gint xdith,
                                             gint ydith);

Draws an RGB image in the drawable, with an adjustment for dither alignment.

This function is useful when drawing dithered images into a window that may be scrolled. Pixel (x, y) will be drawn dithered as if its actual location is (x + xdith, y + ydith). Thus, if you draw an image into a window using zero dither alignment, then scroll up one pixel, subsequent draws to the window should have ydith = 1.

Setting the dither alignment correctly allows updating of small parts of the screen while avoiding visible "seams" between the different dither textures.

gdk_draw_indexed_image ()

void        gdk_draw_indexed_image          (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *buf,
                                             gint rowstride,
                                             GdkRgbCmap *cmap);

Draws an indexed image in the drawable, using a GdkRgbCmap to assign actual colors to the color indices.

gdk_draw_gray_image ()

void        gdk_draw_gray_image             (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *buf,
                                             gint rowstride);

Draws a grayscale image in the drawable.

gdk_draw_rgb_32_image ()

void        gdk_draw_rgb_32_image           (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *buf,
                                             gint rowstride);

Draws a padded RGB image in the drawable. The image is stored as one pixel per 32-bit word. It is laid out as a red byte, a green byte, a blue byte, and a padding byte.

It's unlikely that this function will give significant performance gains in practice. In my experience, the performance gain from having pixels aligned to 32-bit boundaries is cancelled out by the increased memory bandwidth.

enum GdkRgbDither

typedef enum
{
  GDK_RGB_DITHER_NONE,
  GDK_RGB_DITHER_NORMAL,
  GDK_RGB_DITHER_MAX
} GdkRgbDither;

Selects whether or not GdkRgb applies dithering to the image on display. There are three values:

• GDK_RGB_DITHER_NONE: Never use dithering.

• GDK_RGB_DITHER_NORMAL: Use dithering in 8 bits per pixel (and below) only.

• GDK_RGB_DITHER_MAX: Use dithering in 16 bits per pixel and below.

Since GdkRgb currently only handles images with 8 bits per component, dithering on 24 bit per pixel displays is a moot point.

gdk_rgb_cmap_new ()

GdkRgbCmap* gdk_rgb_cmap_new                (guint32 *colors,
                                             gint n_colors);

Creates a new GdkRgbCmap structure. The cmap maps color indexes to RGB colors. If n_colors is less than 256, then images containing color values greater than or equal to n_colors will produce undefined results, including possibly segfaults.

gdk_rgb_cmap_free ()

void        gdk_rgb_cmap_free               (GdkRgbCmap *cmap);

Frees the memory associated with a GdkRgbCmap created by gdk_rgb_cmap_new().

struct GdkRgbCmap

struct GdkRgbCmap {
  guint32 colors[256];
  guchar lut[256]; /* for 8-bit modes */
};

A private data structure which maps color indices to actual RGB colors. This is used only for gdk_draw_indexed_image().

gdk_rgb_gc_set_foreground ()

void        gdk_rgb_gc_set_foreground       (GdkGC *gc,
                                             guint32 rgb);

Sets the foreground color in gc to the specified color (or the closest approximation, in the case of limited visuals).

gdk_rgb_gc_set_background ()

void        gdk_rgb_gc_set_background       (GdkGC *gc,
                                             guint32 rgb);

Sets the background color in gc to the specified color (or the closest approximation, in the case of limited visuals).

gdk_rgb_xpixel_from_rgb ()

gulong      gdk_rgb_xpixel_from_rgb         (guint32 rgb);

Finds the X pixel closest in color to the rgb color specified. This value may be used to set the pixel field of a GdkColor struct.

gdk_rgb_set_install ()

void        gdk_rgb_set_install             (gboolean install);

If install is TRUE, directs GdkRgb to always install a new "private" colormap rather than trying to find a best fit with the colors already allocated. Ordinarily, GdkRgb will install a colormap only if a sufficient cube cannot be allocated.

A private colormap has more colors, leading to better quality display, but also leads to the dreaded "colormap flashing" effect.

gdk_rgb_set_min_colors ()

void        gdk_rgb_set_min_colors          (gint min_colors);

Sets the minimum number of colors for the color cube. Generally, GdkRgb tries to allocate the largest color cube it can. If it can't allocate a color cube at least as large as min_colors, it installs a private colormap.

gdk_rgb_get_visual ()

GdkVisual*  gdk_rgb_get_visual              (void);

Gets the visual chosen by GdkRgb. This visual and the corresponding colormap should be used when creating windows that will be drawn in by GdkRgb.

gdk_rgb_get_cmap ()

GdkColormap* gdk_rgb_get_cmap               (void);

Gets the colormap set by GdkRgb. This colormap and the corresponding visual should be used when creating windows that will be drawn in by GdkRgb.

gdk_rgb_ditherable ()

gboolean    gdk_rgb_ditherable              (void);

Determine whether the visual is ditherable. This function may be useful for presenting a user interface choice to the user about which dither mode is desired; if the display is not ditherable, it may make sense to gray out or hide the corresponding UI widget.

gdk_rgb_set_verbose ()

void        gdk_rgb_set_verbose             (gboolean verbose);

Sets the "verbose" flag. This is generally only useful for debugging.