Simplest solution to perform screen rotation without hardware support is to perform rotation while coping screen backbuffer to frontbuffer (https://git.haiku-os.org/haiku/tree/src/servers/app/drawing/HWInterface.cpp#n381). Also rotation will be needed for screen capture (https://git.haiku-os.org/haiku/tree/src/servers/app/drawing/DrawingEngine.cpp#n1503). BDirectWindow software screen rotation support is not possible and it should be disabled.
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