Description
Low-level display hardware informationDetailed Description
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 (gdkColormapGetVisual), so
you won't have to provide a visual in addition. There are several standard visuals. The visual returned
by gdkVisualGetSystem is the system's default
visual. gdkRgbGetVisual 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
gdkRgbGetColormap). 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.Enums and Flags
GdkVisualType-
A set of values that describe the manner in which the
pixel values for a visual are converted into RGB
values for display.
static-gray- Each pixel value indexes a grayscale value directly.
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.
static-color- Each pixel value is an index into a predefined,
unmodifiable color map that maps pixel values into RGB values.
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.
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. direct-color- Each pixel value contains red, green, and blue
components as for
GDK_VISUAL_TRUE_COLOR, but the components are mapped via a
color table into the final output table instead of being converted directly.
GdkByteOrder-
A set of values describing the possible byte-orders
for storing pixel values in memory.
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.
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.