Control Planes - Compaq PowerStorm 1000 Owner's Manual

6.3.6.4 Control Planes

The PowerStorm 1000 graphics subsystem has several types of control planes:
•
Eight window ID planes
•
One Z buffer erase plane
•
One window clip plane
•
Eight stencil planes
•
Double-buffered 8-bit overlay/blink planes
A control plane is a frame buffer plane that allocates one bit per pixel to perform a
function on a per-pixel basis that controls how a pixel value is written into or read from the
frame buffer.
The Window ID planes allow the application to control various attributes on a window by
window basis. Attributes under control of the window ID planes include:
•
Double buffer control
•
Pixel type (indexed or true color)
•
Several blink/overlay options
The Z buffer Erase Plane allows the frame buffer hardware to mark DRAM locations used
for Z buffering as erased, even if they have not been. This allows the corresponding
VRAM locations to be erased at full speed without waiting for the DRAM to be erased.
The Window Clip Plane allows windows to be updated by the server without requiring all
updates to be compared against a list of clip rectangles for all the areas that overlapping
windows intersect. This allows high performance rendering in a window environment.
The Stencil Planes are used for particular cases where round-off or truncation error can
cause Z-fighting for objects intended to have the same Z-value.
The overlay/blink planes provide a mechanism to display 8-bit visuals without affecting
the existing image in the true color planes. These are double-buffered. They can also
produce a minimal true color approximation in 3/3/2 (R/G/B) configuration.
DIGITAL PowerStorm 1000 Graphics Subsystem Owner's Guide 6–11
Technical Description