Review of #584: the default must not make guest-visible VRAM depend on the
internal scale. Mode 1 ("on", default; "scaled" kept as an alias) now
puts the PS1 pattern on the native VRAM grid; mode 2 ("fine") is the
elective per-internal-pixel pattern. gl_dithering_test checks the default
mode's native VRAM is identical at 4x and 1x (equal-colour Gouraud now
averages 15.50 in the default at every scale). Docs keep the
semi-transparent approximation explicit. OpenBIOS stamp regenerated.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Maintainer review of #584: PS1 dithering is hardware behaviour, so it is
now on by default whenever the guest sets GP0(E1h) bit 9 ([video]
dithering = "on"; "scaled" stays opt-in, "off" is the old true-colour
output).
Eligibility is decided per primitive from its command and carried in the
vertex instead of being inferred from the colour:
- Gouraud polygons and shaded lines: geometry vertex a_col.a + 2*131072
(decoded in GEO_VS, v_dith);
- texture-modulated polygons: a_semi + 8 (v_dith in TEX_VS);
- flat polygons/lines, raw-texture polygons and every rectangle: never.
This fixes the two reproduced bugs (Gouraud with 5-bit-exact colours was
skipped; textured rectangles were dithered). Bit changes no longer flush:
eligibility is fixed when the primitive is queued; mode changes still drain.
gl_dithering_test covers each case (Gouraud incl. equal colours, shaded
line, modulated and neutral-modulated textured polys dithered; flat tri,
flat rect, flat line, raw poly, modulated and raw textured rects never;
bit clear and off unchanged), plus scaled 4x == 1x, render thread, PGXP
depth, native-wide and the accurate-blending basis. OpenBIOS stamp
regenerated.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The OpenGL renderer has always drawn shaded and texture-modulated pixels
at 8 bits per channel with no dither pattern (true colour). That stays the
default. 'on' applies the PS1 4x4 offset matrix and 5-bit truncation per
internal-resolution pixel; 'scaled' puts the pattern on the native grid,
so it reads like the console at any scale and the native VRAM is the same
at every internal resolution.
GP0(E1h) bit 9 reaches the backend through a new optional facade hook
(gr_set_dither) recorded for the render thread and Smooth motion redraws.
With the mode off nothing flushes and no uniform changes. Flat, raw and
other 5-bit-exact pixels are never touched.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Shokunin