GEOS SDK TechDocs|
| 
11.2 Clipping
GrBeginUpdate(), GrEndUpdate()
The kernel provides two messages by which the geode may signal that it is updating the contents of a window. When updating a region (as when handling a
MSG_META_EXPOSED
), the geode should call
GrBeginUpdate()
after creating the GState,
and call
GrEndUpdate()
before destroying the GState.
This causes the system to store the GState for future comparisons during clipping region calculation. If you don't call these functions, the clipping region is likely to be wrong for this and other updates. Default system MSG_META_EXPOSED handlers call these routines.
Note that you only need call these routines when performing a requested update; if you are drawing to a window without being asked to do so, you need not call these routines.
GEOS SDK TechDocs|
| 11.2 Clipping