Default Palette
The
default palette is an array of color values identifying the colors that can be used with a
device context by default. Windows associates the default palette with a context
whenever an application creates a context for a device that supports color
palettes. The default palette ensures that colors are available for use by an
application without any further action.
The default palette typically has 20 entries (colors), but the exact number of
entries may vary from device to device. This number is equal to the NUMCOLORS
value returned by the
GetDeviceCaps function. An application can retrieve the color values for colors in the
default palette by enumerating solid pens, the same technique used to discover the
colors available on nonpalette devices. The colors in the default palette
depend on the device. Display devices, for example, often use the 16 standard colors
of the VGA display and 4 other colors defined by Windows. Printer devices may
use other default colors.
When using the default palette, applications use color values to specify pen
and text colors. If the requested color is not in the palette, Windows
approximates the color by using the closest color in the palette. If an application
requests a solid brush color that is not in the palette, Windows simulates the
color by dithering with colors that are in the palette.
To avoid approximations and dithering, applications can also specify pen,
brush, and text colors by using color palette indices rather than color values. A
color palette index is an integer value that identifies a specific palette
entry. Applications can use color palette indices in place of color values but must
use the
PALETTEINDEX macro to create the indices.
Color palette indices are only useful for devices that support color palettes.
To avoid this device dependence, applications that use the same code to draw
to both palette and nonpalette devices should use palette-relative color values
to specify pen, brush, and text colors. These values are identical to color
values except when creating solid brushes. (On palette devices, a solid brush
color specified by a palette-relative color value is subject to color approximation
instead of dithering.) Applications must use the
PALETTERGB macro to create palette-relative color values.
Windows does not allow an application to change the entries in the default
palette. To use colors other than those in the default palette, an application
must create its own logical palette and select the palette into the device context.
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