The problem can not be solved with DX7. Its a pure hardware restriction. the systems that have problems do not nearly meet the BM minimum requirement for Max2D. They fallback to pure emulation most likely or pretend to DX that they are capable and just fail to really work.
DX7 has no scissor test (the thing that cuts drawing on GL drivers). Using viewports creates problems far larger (thats what I've tried, using real viewports).
What BRL did was using clipplanes like in 3D to restrict the drawing. and the systems that fail on the viewport end actually do so because of their graphic cards that don't support 4 clip planes but only 2 (most likely meant for near and far but no side).
If you only need to restrict the viewport to right and down you could do that and have it working on those systems as you would only need 2 clip planes. but with x,y,width,height in the viewport it wouldn't work I fear
DX7 has no scissor test (the thing that cuts drawing on GL drivers). Using viewports creates problems far larger (thats what I've tried, using real viewports).
What BRL did was using clipplanes like in 3D to restrict the drawing. and the systems that fail on the viewport end actually do so because of their graphic cards that don't support 4 clip planes but only 2 (most likely meant for near and far but no side).
If you only need to restrict the viewport to right and down you could do that and have it working on those systems as you would only need 2 clip planes. but with x,y,width,height in the viewport it wouldn't work I fear