The Video Display List Processor

The Graphics folio component that controls the display generator is the video display list processor (VDLP). It reads the display control commands in the video display list (VDL), and executes them according to their timing: Each command is linked to one line in the video display. During each horizontal blank, the VDLP checks to see what commands in the VDL need to be executed, and then executes them.

The display control commands sets the display mode of the frame buffer, change the contents of the custom CLUT set registers, set the pointer to the location of the frame buffer, and do much more. You'll find details in the graphics programming chapters that follow this one.

In 3DO Portfolio's multitasking environment, multiple tasks can have something to display on the screen at the same time. The VDLP recognizes only one task as the display owner and only allows that task full control, setting CLUT registers and performing other display alterations. Other tasks are subordinate display users and operate under the parameters set by the display owner; they can modify only a small and limited set of display parameters.

This brings us to the end of the detailed look at the display generator. You'll find programming information about the display generator in Using the Display Generator. The next chapter is another overview chapter, this one containing details about the cel engine.