3 people cf804c4b27 feat(brush): Photoshop's measured round tip (#4617) ...

Photoshop 27.11's round tip, measured on single dabs (hardness 0-100 in
steps of 10 at 40 px, checked at 100, 9, 7, 5, 3, 2 and 1 px): a solid
core of radius r0*R, then a Gaussian shoulder exp(-((d - r0) / s)^2) of
width s*R, both from a table by hardness. A soft tip reaches well past its
nominal radius (hardness 0 is a Gaussian of sigma 0.47 R: 8 % at 1.05 R);
PhotoCraft's (1 - t^2)^4 ended at R and kept far less coverage (a 40 px
hardness-0 dab held 251 coverage units against Photoshop's 542). The edge
stays at least ~1 px wide (0.3 R on small tips, never under 1/4 px).
exp is (1 - u/64)^64 by squaring, so it is the same on every platform.

Dab rectangles, reaches and the retouch footprint grow to the tip's reach
(tip_reach); the brush cursor's 50 % ring (half_coverage_radius) follows the
new curve. Tests that hard-coded the old curve now check measured values;
tests that bounded a stroke by the nominal radius use the reach.

Measured against Photoshop (max levels / mean): 40 px dabs, hardness 0-70:
70-156 / 12-15 -> 2-6.5 / <0.7; 100 px dabs 70-177 -> 2-27; strokes
(probe 13) soft and medium 20-60 px 133-178 / up to 17 -> 4-26 / <=0.5;
spacing sweeps 134-221 -> 7-9; soft Flow build-up 85 / 7.5 -> 5 / 0.16;
small 1-7 px total error lower in 21 of 30 cases (medium hardness at
2-5 px a little higher: a follow-up).

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

2026-10-13 01:14:26 -04:00

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tests.rs

feat(brush): Photoshop's measured round tip (#4617)

2026-10-13 01:14:26 -04:00