Low-level display hardware information
A <gdk-visual> 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 <gdk-image>, but you should avoid
<gdk-image> precisely because its contents depend on the display
hardware; use <gdk-pixbuf> instead, for all but the most low-level
purposes. Also, anytime you provide a <gdk-colormap>, 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 <gdk-rgb>, 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’.
glist-of)Lists the available visuals for the default screen. (See
gdk-screen-list-visuals) A visual describes a hardware image data format. For example, a visual might support 24-bit color, or 8-bit color, and might expect pixels to be in a certain format.Call
g-list-freeon the return value when you're finished with it.
- ret
- a list of visuals; the list must be freed, but not its contents
int)Get the best available depth for the default GDK screen. "Best" means "largest," i.e. 32 preferred over 24 preferred over 8 bits per pixel.
- ret
- best available depth
<gdk-visual-type>)Return the best available visual type for the default GDK screen.
- ret
- best visual type
<gdk-visual>)Get the system'sdefault visual for the default GDK screen. This is the visual for the root window of the display. The return value should not be freed.
- ret
- system visual
<gdk-visual>)Get the visual with the most available colors for the default GDK screen. The return value should not be freed.
- ret
- best visual
int) ⇒ (ret <gdk-visual>)Get the best visual with depth depth for the default GDK screen. Color visuals and visuals with mutable colormaps are preferred over grayscale or fixed-colormap visuals. The return value should not be freed. ‘
#f’ may be returned if no visual supports depth.
- depth
- a bit depth
- ret
- best visual for the given depth
<gdk-visual-type>) ⇒ (ret <gdk-visual>)Get the best visual of the given visual-type for the default GDK screen. Visuals with higher color depths are considered better. The return value should not be freed. ‘
#f’ may be returned if no visual has type visual-type.
- visual-type
- a visual type
- ret
- best visual of the given type