Visuals
Low-level display hardware information
A #GdkVisual describes a particular video hardware display format. It includes
information about the number of bits used for each color, the way the bits are
translated into an RGB value for display, and the way the bits are stored in
memory. For example, a piece of display hardware might support 24-bit color,
16-bit color, or 8-bit color; meaning 24/16/8-bit pixel sizes. For a given
pixel size, pixels can be in different formats; for example the "red" element
of an RGB pixel may be in the top 8 bits of the pixel, or may be in the lower
4 bits.
Usually you can avoid thinking about visuals in GTK+. Visuals are useful to
interpret the contents of a #GdkImage, but you should avoid #GdkImage precisely
because its contents depend on the display hardware; use #GdkPixbuf instead, for
all but the most low-level purposes. Also, anytime you provide a #GdkColormap,
the visual is implied as part of the colormap (gdk_colormap_get_visual()), so
you won't have to provide a visual in addition.
There are several standard visuals. The visual returned
by gdk_visual_get_system() is the system's default
visual. gdk_rgb_get_visual() return the visual most
suited to displaying full-color image data. If you
use the calls in #GdkRGB, you should create your windows
using this visual (and the colormap returned by
gdk_rgb_get_colormap()).
A number of functions are provided for determining
the "best" available visual. For the purposes of
making this determination, higher bit depths are
considered better, and for visuals of the same
bit depth, %GDK_VISUAL_PSEUDO_COLOR is preferred at
8bpp, otherwise, the visual types are ranked in the
order of (highest to lowest) %GDK_VISUAL_DIRECT_COLOR,
%GDK_VISUAL_TRUE_COLOR, %GDK_VISUAL_PSEUDO_COLOR,
%GDK_VISUAL_STATIC_COLOR, %GDK_VISUAL_GRAYSCALE,
then %GDK_VISUAL_STATIC_GRAY.
#GdkImage, #GdkColormap, #GdkRGB
The GdkVisual structure contains information about
a particular visual.
Constructing a pixel value from components
guint
pixel_from_rgb (GdkVisual *visual,
guchar r, guchar b, guchar g)
{
return ((r >> (16 - visual->red_prec)) << visual->red_shift) |
((g >> (16 - visual->green_prec)) << visual->green_shift) |
((r >> (16 - visual->blue_prec)) << visual->blue_shift);
}
@parent_instance: inherited portion from #GObject
@type: The type of this visual.
@depth: The number of bits per pixel.
@byte_order: The byte-order for this visual.
@colormap_size: The number of entries in the colormap, for
visuals of type %GDK_VISUAL_PSEUDO_COLOR or
%GDK_VISUAL_GRAY_SCALE. For other visual types, it
is the number of possible levels per color component.
If the visual has different numbers of levels for
different components, the value of this field is undefined.
@bits_per_rgb: The number of significant bits per red, green, or blue
when specifying colors for this visual. (For instance, for
gdk_colormap_alloc_color())
@red_mask: A mask giving the bits in a pixel value that
correspond to the red field. Significant only for
%GDK_VISUAL_PSEUDOCOLOR and %GDK_VISUAL_DIRECTCOLOR.
@red_shift: The red_shift and
red_prec give an alternate presentation
of the information in red_mask.
red_mask is a contiguous sequence
of red_prec bits starting at bit
number red_shift. For example,
shows constructing a pixel value
out of three 16 bit color values.
@red_prec: See above.
@green_mask: A mask giving the bits in a pixel value that
correspond to the green field.
@green_shift: The green_shift and
green_prec give an alternate presentation
of the information in green_mask.
@green_prec: See above.
@blue_mask: A mask giving the bits in a pixel value that
correspond to the blue field.
@blue_shift: The blue_shift and
blue_prec give an alternate presentation
of the information in blue_mask.
@blue_prec: See above.
A set of values that describe the manner in which the
pixel values for a visual are converted into RGB
values for display.
@GDK_VISUAL_STATIC_GRAY: Each pixel value indexes a grayscale value directly.
@GDK_VISUAL_GRAYSCALE: Each pixel is an index into a color map that maps pixel
values into grayscale values. The color map can be changed by an application.
@GDK_VISUAL_STATIC_COLOR: Each pixel value is an index into a predefined,
unmodifiable color map that maps pixel values into RGB values.
@GDK_VISUAL_PSEUDO_COLOR: Each pixel is an index into a color map that maps
pixel values into rgb values. The color map can be changed by an application.
@GDK_VISUAL_TRUE_COLOR: Each pixel value directly contains red, green,
and blue components. The red_mask,
green_mask, and
blue_mask fields of the #GdkVisual
structure describe how the components are assembled into a pixel value.
@GDK_VISUAL_DIRECT_COLOR: Each pixel value contains red, green, and blue
components as for %GDK_TRUE_COLOR, but the components are mapped via a
color table into the final output table instead of being converted directly.
A set of values describing the possible byte-orders
for storing pixel values in memory.
@GDK_LSB_FIRST: The values are stored with the least-significant byte
first. For instance, the 32-bit value 0xffeecc would be stored
in memory as 0xcc, 0xee, 0xff, 0x00.
@GDK_MSB_FIRST: The values are stored with the most-significant byte
first. For instance, the 32-bit value 0xffeecc would be stored
in memory as 0x00, 0xcc, 0xee, 0xff.
@depths:
@count:
@visual_types:
@count:
@Returns:
@Returns:
@Returns:
@Returns:
@Returns:
@depth:
@Returns:
@visual_type:
@Returns:
@depth:
@visual_type:
@Returns:
Deprecated equivalent of g_object_ref().
@v:
@Returns:
Deprecated equivalent of g_object_unref().
@v: