perf(vello_cpu): statically dispatch f32 image sampling quality
#1343
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By using a `const` generic to dispatch statically between bilinear and
bicubic sampling, we get a 7% timing decrease for bilinear sampling
(medium quality) in the f32 pipeline. It appears not to impact bicubic
sampling (high quality).
The benchmark was performed by temporarily adding medium and high
quality variants of `transform::rotate` in
`sparse_strips/vello_bench/src/fine/image.rs`.
```
fine/image/transform/rotate_medium_f32_scalar
time: [10.142 µs 10.149 µs 10.157 µs]
change: [-7.5294% -7.3741% -7.2353%] (p = 0.00 < 0.05)
Performance has improved.
Found 26 outliers among 100 measurements (26.00%)
4 (4.00%) low severe
9 (9.00%) low mild
6 (6.00%) high mild
7 (7.00%) high severe
Benchmarking fine/image/transform/rotate_high_f32_scalar: Collecting 100 samples in estimated 5.0357 s (162k iterfine/image/transform/rotate_high_f32_scalar
time: [31.144 µs 31.175 µs 31.215 µs]
change: [-0.3454% +0.1490% +0.4994%] (p = 0.57 > 0.05)
No change in performance detected.
Found 14 outliers among 100 measurements (14.00%)
2 (2.00%) high mild
12 (12.00%) high severe
```
LaurenzV
approved these changes
Jan 7, 2026
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By using a
constgeneric to dispatch statically between bilinear and bicubic sampling, on x86 we get a 7% timing decrease for bilinear sampling (medium quality) in the f32 pipeline. It appears not to impact timings for bicubic sampling (high quality).The benchmark was performed by temporarily adding medium and high quality variants of
transform::rotateinsparse_strips/vello_bench/src/fine/image.rs.