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GdkRGB

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

Synopsis


#include <gdk/gdk.h>


void        gdk_rgb_init                    (void);

void        gdk_draw_rgb_image              (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *rgb_buf,
                                             gint rowstride);
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);
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);
void        gdk_draw_gray_image             (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *buf,
                                             gint rowstride);
void        gdk_draw_rgb_32_image           (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *buf,
                                             gint rowstride);
void        gdk_draw_rgb_32_image_dithalign (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *buf,
                                             gint rowstride,
                                             gint xdith,
                                             gint ydith);
enum        GdkRgbDither;

GdkRgbCmap* gdk_rgb_cmap_new                (guint32 *colors,
                                             gint n_colors);
void        gdk_rgb_cmap_free               (GdkRgbCmap *cmap);
            GdkRgbCmap;

void        gdk_rgb_gc_set_foreground       (GdkGC *gc,
                                             guint32 rgb);
void        gdk_rgb_gc_set_background       (GdkGC *gc,
                                             guint32 rgb);
gulong      gdk_rgb_xpixel_from_rgb         (guint32 rgb);
void        gdk_rgb_find_color              (GdkColormap *colormap,
                                             GdkColor *color);

void        gdk_rgb_set_install             (gboolean install);
void        gdk_rgb_set_min_colors          (gint min_colors);
GdkVisual*  gdk_rgb_get_visual              (void);
GdkColormap* gdk_rgb_get_colormap           (void);
#define     gdk_rgb_get_cmap
gboolean    gdk_rgb_ditherable              (void);
gboolean    gdk_rgb_colormap_ditherable     (GdkColormap *cmap);
void        gdk_rgb_set_verbose             (gboolean verbose);

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_pixbuf_render_to_drawable() 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.

Example 4. A simple example program using GdkRGB

#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;
}

Details

gdk_rgb_init ()

void        gdk_rgb_init                    (void);

Warning

gdk_rgb_init is deprecated and should not be used in newly-written code.

This function no longer does anything at all. It's completely useless (and harmless).


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.

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].

drawable :The GdkDrawable to draw in (usually a GdkWindow).
gc :The graphics context (all GDK drawing operations require one; its contents are ignored).
x :The x coordinate of the top-left corner in the drawable.
y :The y coordinate of the top-left corner in the drawable.
width :The width of the rectangle to be drawn.
height :The height of the rectangle to be drawn.
dith :A GdkRgbDither value, selecting the desired dither mode.
rgb_buf :The pixel data, represented as packed 24-bit data.
rowstride :The number of bytes from the start of one row in rgb_buf to the start of the next.

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.

drawable :The GdkDrawable to draw in (usually a GdkWindow).
gc :The graphics context.
x :The x coordinate of the top-left corner in the drawable.
y :The y coordinate of the top-left corner in the drawable.
width :The width of the rectangle to be drawn.
height :The height of the rectangle to be drawn.
dith :A GdkRgbDither value, selecting the desired dither mode.
rgb_buf :The pixel data, represented as packed 24-bit data.
rowstride :The number of bytes from the start of one row in rgb_buf to the start of the next.
xdith :An x offset for dither alignment.
ydith :A y offset for dither alignment.

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.

drawable :The GdkDrawable to draw in (usually a GdkWindow).
gc :The graphics context.
x :The x coordinate of the top-left corner in the drawable.
y :The y coordinate of the top-left corner in the drawable.
width :The width of the rectangle to be drawn.
height :The height of the rectangle to be drawn.
dith :A GdkRgbDither value, selecting the desired dither mode.
buf :The pixel data, represented as 8-bit color indices.
rowstride :The number of bytes from the start of one row in buf to the start of the next.
cmap :The GdkRgbCmap used to assign 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.

drawable :The GdkDrawable to draw in (usually a GdkWindow).
gc :The graphics context.
x :The x coordinate of the top-left corner in the drawable.
y :The y coordinate of the top-left corner in the drawable.
width :The width of the rectangle to be drawn.
height :The height of the rectangle to be drawn.
dith :A GdkRgbDither value, selecting the desired dither mode.
buf :The pixel data, represented as 8-bit gray values.
rowstride :The number of bytes from the start of one row in buf to the start of the next.

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.

drawable :The GdkDrawable to draw in (usually a GdkWindow).
gc :The graphics context.
x :The x coordinate of the top-left corner in the drawable.
y :The y coordinate of the top-left corner in the drawable.
width :The width of the rectangle to be drawn.
height :The height of the rectangle to be drawn.
dith :A GdkRgbDither value, selecting the desired dither mode.
buf :The pixel data, represented as padded 32-bit data.
rowstride :The number of bytes from the start of one row in buf to the start of the next.

gdk_draw_rgb_32_image_dithalign ()

void        gdk_draw_rgb_32_image_dithalign (GdkDrawable *drawable,
                                             GdkGC *gc,
                                             gint x,
                                             gint y,
                                             gint width,
                                             gint height,
                                             GdkRgbDither dith,
                                             guchar *buf,
                                             gint rowstride,
                                             gint xdith,
                                             gint ydith);

Like gdk_draw_rgb_32_image(), but allows you to specify the dither offsets. See gdk_draw_rgb_image_dithalign() for more details.

drawable : a GdkDrawable
gc : a GdkGC
x : X coordinate on drawable where image should go
y : Y coordinate on drawable where image should go
width : width of area of image to draw
height : height of area of image to draw
dith : dithering mode
buf : RGB image data
rowstride : rowstride of RGB image data
xdith : X dither offset
ydith : Y dither offset

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.

colors :The colors, represented as 0xRRGGBB integer values.
n_colors :The number of colors in the cmap.
Returns :The newly created GdkRgbCmap

gdk_rgb_cmap_free ()

void        gdk_rgb_cmap_free               (GdkRgbCmap *cmap);

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

cmap :The GdkRgbCmap to free.

GdkRgbCmap

typedef struct {
  guint32 colors[256];
  gint n_colors;
} GdkRgbCmap;

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);

Warning

gdk_rgb_gc_set_foreground is deprecated and should not be used in newly-written code.

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

gc :The GdkGC to modify.
rgb :The color, represented as a 0xRRGGBB integer value.

gdk_rgb_gc_set_background ()

void        gdk_rgb_gc_set_background       (GdkGC *gc,
                                             guint32 rgb);

Warning

gdk_rgb_gc_set_background is deprecated and should not be used in newly-written code.

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

gc :The GdkGC to modify.
rgb :The color, represented as a 0xRRGGBB integer value.

gdk_rgb_xpixel_from_rgb ()

gulong      gdk_rgb_xpixel_from_rgb         (guint32 rgb);

Warning

gdk_rgb_xpixel_from_rgb is deprecated and should not be used in newly-written code.

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.

rgb :The color, represented as a 0xRRGGBB integer value.
Returns :The X pixel value.

gdk_rgb_find_color ()

void        gdk_rgb_find_color              (GdkColormap *colormap,
                                             GdkColor *color);

colormap should be the colormap for the graphics context and drawable you're using to draw. If you're drawing to a GtkWidget, call gtk_widget_get_colormap().

color should have its red, green, and blue fields initialized; gdk_rgb_find_color() will fill in the pixel field with the best matching pixel from a color cube. The color is then ready to be used for drawing, e.g. you can call gdk_gc_set_foreground() which expects pixel to be initialized.

In many cases, you can avoid this whole issue by calling gdk_gc_set_rgb_fg_color() or gdk_gc_set_rgb_bg_color(), which do not expect pixel to be initialized in advance. If you use those functions, there's no need for gdk_rgb_find_color().

colormap : a GdkColormap
color : a GdkColor

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.

install :TRUE to set install mode.

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.

min_colors :The minimum number of colors accepted.

gdk_rgb_get_visual ()

GdkVisual*  gdk_rgb_get_visual              (void);

Gets a "preferred visual" chosen by GdkRGB for rendering image data on the default screen. In previous versions of GDK, this was the only visual GdkRGB could use for rendering. In current versions, it's simply the visual GdkRGB would have chosen as the optimal one in those previous versions. GdkRGB can now render to drawables with any visual.

Returns : The GdkVisual chosen by GdkRGB.

gdk_rgb_get_colormap ()

GdkColormap* gdk_rgb_get_colormap           (void);

Get the preferred colormap for rendering image data. Not a very useful function; historically, GDK could only render RGB image data to one colormap and visual, but in the current version it can render to any colormap and visual. So there's no need to call this function.

Returns : the preferred colormap

gdk_rgb_get_cmap

#define gdk_rgb_get_cmap               gdk_rgb_get_colormap

Warning

gdk_rgb_get_cmap is deprecated and should not be used in newly-written code.

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.

Returns :The GdkColormap set by GdkRGB.

gdk_rgb_ditherable ()

gboolean    gdk_rgb_ditherable              (void);

Determines whether the preferred 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.

Returns :TRUE if the preferred visual is ditherable.

gdk_rgb_colormap_ditherable ()

gboolean    gdk_rgb_colormap_ditherable     (GdkColormap *cmap);

Determines whether the visual associated with cmap 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.

cmap :a GdkColormap
Returns :TRUE if the visual associated with cmap is ditherable.

gdk_rgb_set_verbose ()

void        gdk_rgb_set_verbose             (gboolean verbose);

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

verbose :TRUE if verbose messages are desired.

See Also

GdkColor

The underlying GDK mechanism for allocating colors.

GdkPixbuf and gdk_pixbuf_render_to_drawable()

Higher-level image handling.