Relative safety margin applied to the peak scale before the footprint
radius is derived from it (see gsplatVisibleMahalSq). The fragment
reads the amplitude and alpha through mediump varyings (fp16 on mobile
GPUs: relative rounding 2^-11 ≈ 4.9e-4) and evaluates exp/log at GPU
precision. The worst case is the volumetric alpha → optical-density map
w = −ln(1 − a): half an fp16 ulp of a near ALPHA_CLAMP moves w by up to
2^-12·512 ≈ 0.125 of its ≈ 6.24, i.e. 2%. A 5% margin covers that with
headroom, while costing only 2·ln(1.05) ≈ 0.1 in the squared radius of a
splat that is dim enough to be tightened at all (bright splats keep T).
Relative safety margin applied to the peak scale before the footprint radius is derived from it (see gsplatVisibleMahalSq). The fragment reads the amplitude and alpha through
mediumpvaryings (fp16 on mobile GPUs: relative rounding 2^-11 ≈ 4.9e-4) and evaluatesexp/logat GPU precision. The worst case is the volumetric alpha → optical-density map w = −ln(1 − a): half an fp16 ulp ofanearALPHA_CLAMPmoves w by up to 2^-12·512 ≈ 0.125 of its ≈ 6.24, i.e. 2%. A 5% margin covers that with headroom, while costing only 2·ln(1.05) ≈ 0.1 in the squared radius of a splat that is dim enough to be tightened at all (bright splats keep T).