rect_union_add takes a pixman_box32_t by value, and passes it along by
value to internal helpers. render_pass_mark_box_updated which is the
only caller receives the pixman_box32_t by reference, so just plumb it
through that way.
Results in a 13% improvement in CPU time when using the Vulkan renderer
on the stacked/clip200/1024 benchmarks on my machine.
Signed-off-by: Kenny Levinsen <kl@kl.wtf>
The new struct rect_union is designed to make it easier to
efficiently accumulate a list of rectangles, and then operate
on an exact cover of their union.
Using rect_union, the times needed to added t rectangles, and then
compute their exact cover will be O(t), and something between Ω(t) and
O(t^2), depending on the rectangle arrangement. If one tries to do
the same by storing a pixman_region32_t and updating it with
pixman_region32_union_rect(), then total time needed would be between
Ω(t^2) and O(t^3), depending on the input. Without changing the public
API (data structure + rectangle ordering rules) for pixman_region32_t,
it is impossible to improve its worst case time.
