Solaris Handbook for Sun Frame Buffers

Single Color LUT

CG14 has two hardware color LUTs. One is used by the 8-bit underlay visuals and the other is used by the 8-bit overlay visual. In contrast, the Creator accelerator Series 1 and 2 have only one hardware color LUT. This means that an overlay window on the Creator accelerator will colormap flash against an 8-bit underlay window unless precautions are taken to make sure that the colormaps of the two windows use the same colors in the same pixel locations. Creator series 3 has four hardware color LUTs whose allocation and sharing is managed by the Xserver.

When programming for the case where there is only one color LUT on a Creator accelerator, take precautions to share overlay and underlay colors on transparent overlay applications. Since the overlay visual is always a different visual from the underlay visual, a transparent overlay application always requires at least two separate colormaps: one for the overlay and one for the underlay. The overlay window is usually a child of the underlay window and the pixels are correlated (i.e., spatially congruent) by the application. In this situation, when the mouse pointer is inside the boundary of the underlay and overlay window pair, the overlay colormap will be installed in the hardware CLUT and the underlay colormap will not be installed. Thus, take care to ensure that underlay pixels display the correct colors when viewed through the overlay colormap. This can be done by allocating colors in the same position in both the underlay and overlay colormaps.