Ramdac - Matrox Corona Installation And Hardware Reference

The display section 57
The frame buffer's dual-ported design allows it to accept data
from the graphics display controller and refresh the screen
simultaneously, increasing display speed and performance.
You can overlay 24-bit true-color text and graphics on the image
frame buffer using a specified color key. The key color can be
set using the MIL-Lite MdispOverlayKey() command.
To configure the overlay frame buffer to the desired resolution,
use the VGA setup (see Chapter 4 - MGA Display Properties
and MGA PowerDesk). The image frame buffer automatically
uses the same resolution. If you are not using Matrox Corona
as the main VGA display controller, set the resolution of the
display using the MIL-Lite MdispAlloc() command.
You can move images larger than the display resolution around
using pan and scroll operations. In addition, you can zoom in
on images by a factor of 2 or 4. These effects will be applied on
both the image and overlay frame buffers. Note that zoom, pan,
and scroll operations are only display effects and do not modify
the data in the frame buffers.

RAMDAC

The RAMDAC is a 128-bit Video Interface Palette (VIP) that
provides two 64-bit pixel ports for use in a dual split frame
buffer architecture.
There is a built-in 3x256x8-bit color look-up table (LUT). In
24-bit or 32-bit pixel mode, it can be applied to either the image
data or the overlay data. Note that if Matrox Corona is in 8-bit
single-screen mode, under Windows, the LUTs are associated
with the overlay frame buffer. The RAMDAC also features color
and luminance keying for non-destructive true-color overlay of
text and graphics over a true-color image (24-bit per pixel
mode). The RAMDAC outputs drive the RGB analog inputs of
the monitor through a shape reconstruction filter for a high
quality display.