[smooth] Minor speedup to smooth rasterizer
This speeds up the smooth rasterizer by avoiding a
conditional branches in the hot path. Namely:
- Define a fixed "null cell" which will be pointed
to whenever the current cell is outside of the current
target region. This avoids a "ras.cell != NULL"
check in the FT_INTEGRATE() macro.
- Also use the null cell as a sentinel at the end of
all ycells[] linked-lists, by setting its x coordinate
to INT_MAX. This avoids a 'if (!cell)' check in
gray_set_cell() as well.
- Slightly change the worker struct fields to perform
a little less operations during rendering.
Example results (on a 2013 Corei5-3337U CPU)
out/ftbench -p -s10 -t5 -bc /usr/share/fonts/truetype/droid/DroidSansFallbackFull.ttf
Before: 5.472 us/op
After: 5.275 us/op
out/ftbench -p -s60 -t5 -bc /usr/share/fonts/truetype/droid/DroidSansFallbackFull.ttf
Before: 17.988 us/op
After: 17.389 us/op
2 files changed
