The software motion video component of the Multimedia Presentation Manager/2 must update bit maps very quickly. The system must be able to play movie files at 15 frames per second or faster, with each frame having a bit map size of 320 x 240 pels or larger.
GPI calls such as GpiBitBlt cannot meet these objectives. A set of DevEscape calls are provided so that the software motion video component can directly update the Video Random Access Memory (VRAM) of packed-pel display adapters.
Most of the movie frames are delta frames, containing only those pels that have changed from the previously displayed frame. By directly updating VRAM, the software motion video component only needs to selectively update a small number of pels in a typical 320 x 240 pel image. This selective updating allows better performance than a GPI call, which requires redrawing of the entire bit map and makes a heavy call/return overhead when updating small runs of pels.
Software motion video DevEscape functions are provided to: