IMB_transform is used by Sequencer (and other places) to do image
translation/rotation/scale on the CPU. This PR speeds up parts of it,
particularly when bilinear filtering is used. No behavior changes are
expected.
- Don't use virtual function calls inside inner loop. The code was using
class hierarchies with virtual calls just to do equivalent of "outside
of image? ignore" and "wrap UV coordinates or not?" decisions. Make those
use non-virtual function based code.
- Simplify pixel sampling functions to only do the work as needed by
anything within Blender codebase. For example, bilinear sampling of uchar
images always uses 4 RGBA channels and never does "UV wrap" logic.
- Bilinear interpolation uchar: completely branchless SIMD code now.
- Bilinear interpolation float: 2x floor() calls instead of 4x floor() +
2x ceil(), and final sample blending is done with SIMD.
Sequencer at 4K UHD resolution, with two image strips that need a transform,
playback framerate:
- Windows Ryzen 5950X: 18.7fps -> 26.2fps (IMB_transform time per frame goes
26.3ms -> 11.2ms)
- Mac M1 Max: 27.3fps -> 31.4fps
At that point the IMB_transform is not the slowest part of where playback
takes time (but rather sequencer effect application etc.).
Note: the amount of _actual code_ got a bit smaller. But I've added 100 lines
of unit tests in BLI_math_interp_test.cc, the bilinear interpolation
functions were only tested very indirectly by CPU compositor template
image tests.
Pull Request: https://projects.blender.org/blender/blender/pulls/115653
1e0bf33b00