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392 lines
10 KiB
Plaintext
392 lines
10 KiB
Plaintext
<!-- ##### SECTION Title ##### -->
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Visuals
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<!-- ##### SECTION Short_Description ##### -->
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manipulation of visuals.
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<!-- ##### SECTION Long_Description ##### -->
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<para>
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The way that the data stored on the screen is stored
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in memory can vary considerably between different X
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servers; some X servers even support multiple formats
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used simultaneously. An X <firstterm>visual</firstterm>
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represents a particular format for screen data.
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It includes information about the number of bits
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used for each color, the way the bits are translated
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into an RGB value for display, and the way the bits
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are stored in memory.
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</para>
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<para>
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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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</para>
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<para>
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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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</para>
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<!-- ##### SECTION See_Also ##### -->
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<para>
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</para>
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<!-- ##### STRUCT GdkVisual ##### -->
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<para>
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The GdkVisual structure contains information about
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a particular visual. It contains the following
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public fields.
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<informaltable pgwide=1 frame="none" role="struct">
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<tgroup cols="2"><colspec colwidth="2*"><colspec colwidth="8*">
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<tbody>
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<row>
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<entry><structfield>type</structfield></entry>
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<entry>The type of this visual.</entry>
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</row>
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<row>
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<entry><structfield>depth</structfield></entry>
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<entry>The number of bits per pixel.</entry>
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</row>
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<row>
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<entry><structfield>byte_order</structfield></entry>
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<entry>The byte-order for this visual.</entry>
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</row>
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<row>
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<entry><structfield>colormap_size</structfield></entry>
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<entry>The number of entries in the colormap, for
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visuals of type GDK_VISUAL_PSEUDO_COLOR or
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GDK_VISUAL_GRAY_SCALE. For other visual types, it
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is the number of possible levels per color component.
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If the visual has different numbers of levels for
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different components, the value of this field is
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undefined.</entry>
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</row>
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<row>
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<entry><structfield>bits_per_rgb</structfield></entry>
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<entry>
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The number of significant bits per red, green, or blue
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when specifying colors for this visual. (For instance,
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for gdk_colormap_alloc_color())
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</entry>
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</row>
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<row>
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<entry><structfield>red_mask</structfield></entry>
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<entry>
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A mask giving the bits in a pixel value that
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correspond to the red field. Significant only for
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%GDK_VISUAL_PSEUDOCOLOR and %GDK_VISUAL_DIRECTCOLOR.
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</entry>
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</row>
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<row>
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<entry><structfield>red_shift, red_prec</structfield></entry>
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<entry>
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The <structfield>red_shift</structfield> and
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<structfield>red_prec</structfield> give an alternate presentation
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of the information in <structfield>red_mask</structfield>.
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<structfield>red_mask</structfield> is a contiguous sequence
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of <structfield>red_prec</structfield> starting at bit
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number <structfield>red_shift</structfield>. For example,
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<xref linkend="rgbmask"> shows constructing a pixel value
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out of three 16 bit color values.
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</entry>
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</row>
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<row>
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<entry><structfield>green_mask</structfield></entry>
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<entry>
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A mask giving the bits in a pixel value that
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correspond to the green field.
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</entry>
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</row>
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<row>
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<entry><structfield>green_shift, green_prec</structfield></entry>
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<entry>
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The <structfield>green_shift</structfield> and
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<structfield>green_prec</structfield> give an alternate presentation
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of the information in <structfield>green_mask</structfield>.
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</entry>
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</row>
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<row>
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<entry><structfield>blue_mask</structfield></entry>
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<entry>
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A mask giving the bits in a pixel value that
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correspond to the blue field.
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</entry>
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</row>
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<row>
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<entry><structfield>blue_shift, blue_prec</structfield></entry>
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<entry>
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The <structfield>blue_shift</structfield> and
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<structfield>blue_prec</structfield> give an alternate presentation
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of the information in <structfield>blue_mask</structfield>.
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</entry>
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</row>
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</tbody></tgroup></informaltable>
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</para>
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<figure float="1" id="rgbmask">
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<title>Constructing a pixel value from components</title>
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<programlisting>
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guint
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pixel_from_rgb (GdkVisual *visual,
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guchar r, guchar b, guchar g)
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{
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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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}
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</programlisting>
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</figure>
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@type:
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@depth:
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@byte_order:
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@colormap_size:
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@bits_per_rgb:
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@red_mask:
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@red_shift:
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@red_prec:
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@green_mask:
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@green_shift:
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@green_prec:
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@blue_mask:
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@blue_shift:
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@blue_prec:
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<!-- ##### ENUM GdkVisualType ##### -->
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<para>
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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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values for display.
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<informaltable pgwide=1 frame="none" role="enum">
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<tgroup cols="2"><colspec colwidth="2*"><colspec colwidth="8*">
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<tbody>
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<row>
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<entry>GDK_VISUAL_STATIC_GRAY</entry>
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<entry>Each pixel value indexes a grayscale value directly.</entry>
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</row>
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<row>
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<entry>GDK_VISUAL_GRAYSCALE</entry>
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<entry>Each pixel is an index into a color map that maps
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pixel values into grayscale values. The color map can
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be changed by an application.</entry>
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</row>
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<row>
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<entry>GDK_VISUAL_STATIC_COLOR</entry>
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<entry>Each pixel value is an index into a predefined,
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unmodifiable color map that maps pixel values into
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rgb values.</entry>
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</row>
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<row>
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<entry>GDK_VISUAL_PSEUDO_COLOR</entry>
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<entry>Each pixel is an index into a color map that maps
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pixel values into rgb values. The color map can
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be changed by an application.</entry>
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</row>
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<row>
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<entry>GDK_TRUE_COLOR</entry>
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<entry>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
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a pixel value.
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.</entry>
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</row>
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<row>
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<entry>GDK_DIRECT_COLOR</entry>
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<entry>Each pixel value contains red, green, and blue
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components as for %GDK_TRUE_COLOR, but the components
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are mapped via a color table into the final output
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table instead of being converted directly..</entry>
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</row>
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</tbody></tgroup></informaltable>
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</para>
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@GDK_VISUAL_STATIC_GRAY:
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@GDK_VISUAL_GRAYSCALE:
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@GDK_VISUAL_STATIC_COLOR:
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@GDK_VISUAL_PSEUDO_COLOR:
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@GDK_VISUAL_TRUE_COLOR:
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@GDK_VISUAL_DIRECT_COLOR:
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<!-- ##### ENUM GdkByteOrder ##### -->
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<para>
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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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<informaltable pgwide=1 frame="none" role="enum">
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<tgroup cols="2"><colspec colwidth="2*"><colspec colwidth="8*">
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<tbody>
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<row>
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<entry>GDK_LSB_FIRST</entry>
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<entry>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.</entry>
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</row>
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<row>
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<entry>GDK_MSB_FIRST</entry>
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<entry>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 0xff, 0xee, 0xcc, 0x00.</entry>
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</row>
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</tbody></tgroup></informaltable>
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</para>
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@GDK_LSB_FIRST:
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@GDK_MSB_FIRST:
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<!-- ##### FUNCTION gdk_query_depths ##### -->
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<para>
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Lists the available color depths. The returned values
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are pointers to static storage and should not be
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modified or freed.
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</para>
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@depths: a location to store a pointer to an array
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holding the available color depths.
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@count: a location to store the number of values in @depths.
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<!-- ##### FUNCTION gdk_query_visual_types ##### -->
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<para>
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Lists the available visual types. The returned values
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are pointers to static storage and should not be
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modified or freed.
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</para>
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@visual_types: a location to store a pointer to an
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array holding the available visual types.
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@count: a location to store the number of values in @visual types.
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<!-- ##### FUNCTION gdk_list_visuals ##### -->
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<para>
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Lists the available visuals.
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</para>
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@Returns: A #GList of the available visuals. The list
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should be freed this list with g_list_free().
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<!-- ##### FUNCTION gdk_visual_get_best_depth ##### -->
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<para>
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Returns the best available color depth.
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</para>
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@Returns: the best available color depth.
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<!-- ##### FUNCTION gdk_visual_get_best_type ##### -->
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<para>
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Returns the best available visual type.
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</para>
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@Returns: the best available visual type.
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<!-- ##### FUNCTION gdk_visual_get_system ##### -->
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<para>
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Returns the system's default visual.
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</para>
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@Returns: the system's default visual.
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<!-- ##### FUNCTION gdk_visual_get_best ##### -->
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<para>
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Returns the best available visual.
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</para>
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@Returns: the best available visual.
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<!-- ##### FUNCTION gdk_visual_get_best_with_depth ##### -->
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<para>
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Returns the best available visual with a certain depth.
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</para>
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@depth: the desired color depth
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@Returns: the best available visual with @depth bits per pixel
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or %NULL if no visuals with that type are available.
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<!-- ##### FUNCTION gdk_visual_get_best_with_type ##### -->
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<para>
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Returns the best available visual of a certain visual type.
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</para>
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@visual_type: the desired visual type.
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@Returns: the visual of the given type with the highest depth
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or %NULL if no visuals of that type are available.
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<!-- ##### FUNCTION gdk_visual_get_best_with_both ##### -->
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<para>
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Returns the best available visual
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</para>
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@depth: the desired visual type.
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@visual_type: the desired depth.
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@Returns: the best available visual with the given depth
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and visual type, or %NULL if no matching visuals are
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available.
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<!-- ##### FUNCTION gdk_visual_ref ##### -->
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<para>
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In theory, increases the reference count of a visual. However,
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the set of visuals is determined statically when GTK+ is
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initialized, so this operation does nothing.
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</para>
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@visual: a #GdkVisual.
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@Returns: @visual.
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<!-- ##### FUNCTION gdk_visual_unref ##### -->
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<para>
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In theory, decreases the reference count of a visual. Like
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gdk_visual_ref(), this operation does nothing.
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</para>
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@visual: a #GdkVisual.
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