WinG allows applications to simulate true 24-bit color on 8-bit devices through the WinG halftoning support APIs, WinGCreateHalftonePalette and WinGCreateHalftoneBrush.
The halftone palette is an identity palette containing a carefully selected ramp of colors optimized for dithering true color images to 8-bit devices. The WinGCreateHalftonePalette function returns a handle to a halftone palette which applications can select and realize into a display device context to take advantage of the halftoning capabilities offered by WinG.
The brushes returned by the WinGCreateHalftoneBrush API use patterns of colors in the halftone palette to create areas of simulated true color on 8-bit devices into which the halftone palette has been selected and realized. The CUBE sample application (in the SAMPLES\CUBE subdirectory of the WinG development kit) uses halftoned brushes to generate a wide range of shaded colors on an 8-bit display.
The halftone palette gives applications a framework for dithering 24-bit images to 8-bit devices. The palette itself is a slightly modified 2.6-bit-per-primary RGB cube, giving 216 halftoned values. The 256-color halftone palette also contains the twenty static colors and a range of gray values.
Given a 24-bit RGB color with 8 bits per primitive, you can find the index of the nearest color in the halftone palette using the following formula:
HalftoneIndex = (Red / 51) + (Green / 51) * 6 + (Blue / 51) * 36;
HalftoneColorIndex = aWinGHalftoneTranslation [HalftoneIndex];
The aWinGHalftoneTranslation vector can be found in the HALFTONE source code. The HALFTONE sample (in the SAMPLES\HALFTONE subdirectory of the WinG development kit) applies an ordered 8x8 dither to a 24-bit image, converting it to an 8-bit DIB using the WinG Halftone Palette.
Applications should avoid depending on a specific ordering of the halftone palette by using PALETTERGB instead of PALETTEINDEX to refer to entries in the palette.