(*Image).At can be unnecessarily slow since this tries to get
pixels from GPU. This change reduces the chance to read GPU by
using its pending pixels when possible.
Fixes#1137
This simple change brings my simple test project from 752 allocations per frame to 474 allocations per frame. It seems a shame that go's escape analysis is not smart enough to leave this variable on the stack.
GeoM is a 24-byte struct and there is a slight perf difference that we are storing it in stack, but also copying it around with this change (instead of an 8-byte pointer). This could make things faster (due to stack / CPU cache) or slower (due to copying more memory) - when I try a stress test (drawing 100K images per frame), I can't see any actual performance difference (but I do see 100K fewer allocations, and GC is no longer running almost all the time).
Now grpahicscommand saves the error and shows the error after a
while. This was good to simplify the API but was the cause to hide
some issues.
This change fixes all the errors to be returned immediately, and
buffer this in the ebiten package instead.
Fixes#971
Mipmap calculation must be executed after the main loop starts
because the graphics driver's HasHighPrecisionFloat is needed.
Then, operations on mipmap images must be called from images in
buffered package.
Updates #1044
