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feat(A.5 T20): MSAA 4x + alpha-to-coverage on foliage

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Per Phase A.5 spec §4.9.2: ClipMap foliage uses binary alpha-cutoff.
At N₂=12 horizon distance the pixel-stepped silhouettes are visible.
A2C with MSAA 4x produces smooth retail-faithful tree edges.

GL context now requests Samples=4. WbDrawDispatcher's opaque pass
toggles GL_SAMPLE_ALPHA_TO_COVERAGE on/off around the multi-draw
indirect call. mesh_modern.frag's opaque pass now discards only
truly-empty (α<0.05) so the GPU derives sample mask from coverage;
transparent pass boundary logic is unchanged.

MSAA audit: no custom FBOs found — all rendering uses default
framebuffer. Sky/particles/ImGui are all MSAA-compatible.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-05-10 08:25:59 +02:00
parent 4b84e5650b
commit 26b2871b10
3 changed files with 10 additions and 1 deletions
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5
src/AcDream.App/Rendering/Shaders/mesh_modern.frag
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@ -80,8 +80,11 @@ void main() {
vec4 color = texture(tex, vec3(vTexCoord, float(vTextureLayer)));
// Two-pass alpha-test (N.5 Decision 2).
// A.5 T20: opaque pass writes alpha as-sampled so GL_SAMPLE_ALPHA_TO_COVERAGE
// derives the MSAA sample mask from it — ClipMap foliage edges become smooth.
// Discard only fully-transparent (α < 0.05); the GPU handles coverage masking.
if (uRenderPass == 0) {
if (color.a < 0.95) discard; // opaque pass
if (color.a < 0.05) discard; // opaque pass — kill truly empty only (A2C)
} else {
if (color.a >= 0.95) discard; // transparent pass
if (color.a < 0.05) discard; // skip totally-empty