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<!-- ##### SECTION Title ##### -->
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<!-- ##### SECTION Short_Description ##### -->
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Low-level display hardware information
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<!-- ##### SECTION Long_Description ##### -->
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A #GdkVisual describes a particular video hardware display format. It includes
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information about the number of bits used for each color, the way the bits are
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translated into an RGB value for display, and the way the bits are stored in
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memory. For example, a piece of display hardware might support 24-bit color,
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16-bit color, or 8-bit color; meaning 24/16/8-bit pixel sizes. For a given
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pixel size, pixels can be in different formats; for example the "red" element
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of an RGB pixel may be in the top 8 bits of the pixel, or may be in the lower
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Usually you can avoid thinking about visuals in GTK+. Visuals are useful to
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interpret the contents of a #GdkImage, but you should avoid #GdkImage precisely
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because its contents depend on the display hardware; use #GdkPixbuf instead, for
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all but the most low-level purposes. Also, anytime you provide a #GdkColormap,
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the visual is implied as part of the colormap (gdk_colormap_get_visual()), so
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you won't have to provide a visual in addition.
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There are several standard visuals. The visual returned
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by gdk_visual_get_system() is the system's default
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visual. gdk_rgb_get_visual() return the visual most
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suited to displaying full-color image data. If you
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use the calls in #GdkRGB, you should create your windows
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using this visual (and the colormap returned by
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gdk_rgb_get_colormap()).
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A number of functions are provided for determining
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the "best" available visual. For the purposes of
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making this determination, higher bit depths are
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considered better, and for visuals of the same
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bit depth, %GDK_VISUAL_PSEUDO_COLOR is preferred at
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8bpp, otherwise, the visual types are ranked in the
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order of (highest to lowest) %GDK_VISUAL_DIRECT_COLOR,
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%GDK_VISUAL_TRUE_COLOR, %GDK_VISUAL_PSEUDO_COLOR,
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%GDK_VISUAL_STATIC_COLOR, %GDK_VISUAL_GRAYSCALE,
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then %GDK_VISUAL_STATIC_GRAY.
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<!-- ##### SECTION See_Also ##### -->
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#GdkImage, #GdkColormap, #GdkRGB
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<!-- ##### SECTION Stability_Level ##### -->
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<!-- ##### SECTION Image ##### -->
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<!-- ##### STRUCT GdkVisual ##### -->
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The <type>GdkVisual</type> structure contains information about
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<example id="rgbmask">
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<title>Constructing a pixel value from components</title>
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pixel_from_rgb (GdkVisual *visual,
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guchar r, guchar b, guchar g)
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return ((r >> (16 - visual->red_prec)) << visual->red_shift) |
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((g >> (16 - visual->green_prec)) << visual->green_shift) |
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((r >> (16 - visual->blue_prec)) << visual->blue_shift);
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@parent_instance: inherited portion from #GObject
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<!-- ##### ENUM GdkVisualType ##### -->
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A set of values that describe the manner in which the
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pixel values for a visual are converted into RGB
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@GDK_VISUAL_STATIC_GRAY: Each pixel value indexes a grayscale value directly.
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@GDK_VISUAL_GRAYSCALE: Each pixel is an index into a color map that maps pixel
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values into grayscale values. The color map can be changed by an application.
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@GDK_VISUAL_STATIC_COLOR: Each pixel value is an index into a predefined,
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unmodifiable color map that maps pixel values into RGB values.
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@GDK_VISUAL_PSEUDO_COLOR: Each pixel is an index into a color map that maps
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pixel values into rgb values. The color map can be changed by an application.
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@GDK_VISUAL_TRUE_COLOR: Each pixel value directly contains red, green,
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and blue components. The <structfield>red_mask</structfield>,
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<structfield>green_mask</structfield>, and
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<structfield>blue_mask</structfield> fields of the #GdkVisual
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structure describe how the components are assembled into a pixel value.
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@GDK_VISUAL_DIRECT_COLOR: Each pixel value contains red, green, and blue
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components as for %GDK_VISUAL_TRUE_COLOR, but the components are mapped via a
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color table into the final output table instead of being converted directly.
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<!-- ##### ENUM GdkByteOrder ##### -->
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A set of values describing the possible byte-orders
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for storing pixel values in memory.
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@GDK_LSB_FIRST: The values are stored with the least-significant byte
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first. For instance, the 32-bit value 0xffeecc would be stored
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in memory as 0xcc, 0xee, 0xff, 0x00.
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@GDK_MSB_FIRST: The values are stored with the most-significant byte
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first. For instance, the 32-bit value 0xffeecc would be stored
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in memory as 0x00, 0xcc, 0xee, 0xff.
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<!-- ##### FUNCTION gdk_query_depths ##### -->
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<!-- ##### FUNCTION gdk_query_visual_types ##### -->
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<!-- ##### FUNCTION gdk_list_visuals ##### -->
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<!-- ##### FUNCTION gdk_visual_get_best_depth ##### -->
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<!-- ##### FUNCTION gdk_visual_get_best_type ##### -->
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<!-- ##### FUNCTION gdk_visual_get_system ##### -->
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<!-- ##### FUNCTION gdk_visual_get_best ##### -->
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<!-- ##### FUNCTION gdk_visual_get_best_with_depth ##### -->
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<!-- ##### FUNCTION gdk_visual_get_best_with_type ##### -->
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<!-- ##### FUNCTION gdk_visual_get_best_with_both ##### -->
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<!-- ##### MACRO gdk_visual_ref ##### -->
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Deprecated equivalent of g_object_ref().
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@Returns: the same visual
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<!-- ##### MACRO gdk_visual_unref ##### -->
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Deprecated equivalent of g_object_unref().
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<!-- ##### FUNCTION gdk_visual_get_screen ##### -->
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<!-- ##### FUNCTION gdk_visual_get_bits_per_rgb ##### -->
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<!-- ##### FUNCTION gdk_visual_get_blue_pixel_details ##### -->
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<!-- ##### FUNCTION gdk_visual_get_byte_order ##### -->
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<!-- ##### FUNCTION gdk_visual_get_colormap_size ##### -->
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<!-- ##### FUNCTION gdk_visual_get_depth ##### -->
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<!-- ##### FUNCTION gdk_visual_get_green_pixel_details ##### -->
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<!-- ##### FUNCTION gdk_visual_get_red_pixel_details ##### -->
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<!-- ##### FUNCTION gdk_visual_get_visual_type ##### -->
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docs/reference/gdk/tmpl/visuals.sgml
