A SkPaint runs its shader BEFORE its colourFilter, so setting the exposure
matrix on the same paint as the tone shader landed the gain after the tone
pass: HIGHLIGHT -10 rolled a bright pixel back to 0.78, +EXPOSURE then
multiplied it by 1.2 and +0.15 and it clamped back to 1.0 — the HIGHLIGHT
slider looked dead the moment exposure went up.
The matrix now renders into its own image and the tone/cinema chain samples
that. Measured on the real engine (HIGHLIGHT -10 first, then EXPOSURE +10):
top end stays 0.780 (was 1.000), midtone 0.502 -> 0.722.
3dtours
8e6c1493e8