Region Management and Screen Updating

ADVANCED TOPICS

Region Management and Screen Updating

Only the portions of the screen that change get rendered. This makes many operations, such as modifying and dragging items, or panning the view, much more efficient. Panning is optimized by shifting the pixels in the appropriate direction and then re-rendering just the strips left blank. This optimization can be turned off with the -fastPan widget configuration option. Zooming speed is not improved by this process because it requires re-rendering the entire view.

Screen updating is controlled by region management which uses the concepts of damage and repair. When an item changes, the region within its bounding box is automatically damaged. The act of damaging a region adds it to a list that gets scheduled for repair. The repair doesn't occur until either the system is idle, or the update command is called. Many commands implicitly damage items, but damage can be triggered manually with the damage command.

Pad++ Programmer's Guide - 10 JUN 1996

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