Internal-wm/rootless observations

Alexander Gottwald
Thu Dec 2 19:35:00 GMT 2004

Alexander Gottwald wrote:

> Maybe the odd window width is the problem.

Thinking about it revealed that each pixmap line _must_ start at a boundary.

assuming 8bit mode and a window with width 1 at (0, 0)

pixmap starts at 0x100
screen base is at 0x100 (no problem)

moving the pixmap by 4 pixel down
screen base is 0xfc now

moving 1 pixel up
screen base is still 0xfc

We have no way to distinguish where to start. fbCopyNtoN just adds the
stride size to the base and lands somewhere in the wild. But each line must
begin at a 32 bit boundary and distinct lines must have distinct offsets.

ensuring the pixmap width (in bytes) is always a multiple of 4. Every line
starts at a 32bit boundary.

NP: In Strict Confidence - Sleepless
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