improve xinerama once more? #673
Description
I have found another problem with the xinerama code, see attached image.
The light blue area in the lower left screen of the screenshot is invisible in reality on my setup because the left screen is only 1080 in height. That's all ok. The problem is, that our (fixed in #670) xinerama code should increase the xinerama height of the left screen to the full 900 because is partly in the invisible area (I hope you understand the explanation).
I am not sure about the correct solution. Sunweaver's suggestion about an inner bounding box (see #670) could probably help here but will it help in any case?
I think we need to check these cases after the intersection
a) intersection edge is within the inner bounding box - nothing to do, take intersection result
b) intersection edge is outside the inner bounding box change intersection - increase height
(I have just tried and failed; turns out calculation of the inner bounding box is more complicated than it appears on first thought.)