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Mention why PrimDepth is used in PreRender_FetchFbufCoverage (#1520)

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* Mention why PrimDepth is used in PreRender_FetchFbufCoverage

* Clarify that this only affects the memory alpha blender input, not all alpha blender inputs

* Try to make the subtle difference between coverage and memory alpha more clear
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Tharo 2023-08-15 06:21:12 +01:00 committed by GitHub
parent 6e7a6d4181
commit 18d609c1a3
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1 changed files with 9 additions and 4 deletions
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13
src/code/PreRender.c
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@ -361,7 +361,11 @@ void PreRender_FetchFbufCoverage(PreRender* this, Gfx** gfxp) {
Gfx* gfx = *gfxp; Gfx* gfx = *gfxp;
gDPPipeSync(gfx++); gDPPipeSync(gfx++);
// Set the blend color to full white and set maximum depth // Set the blend color to full white and set maximum depth.
// It is important that at least dz is set to full here as the blender will shift memory alpha values based on the
// value of dz even if depth compare is disabled. If per-pixel depth was enabled, fill rectangle always uses 0 z/dz,
// causing a maximal shift of 4 to be applied to the memory alpha value. Full dz results in no shift, which is
// desired here.
gDPSetBlendColor(gfx++, 255, 255, 255, 8); gDPSetBlendColor(gfx++, 255, 255, 255, 8);
gDPSetPrimDepth(gfx++, 0xFFFF, 0xFFFF); gDPSetPrimDepth(gfx++, 0xFFFF, 0xFFFF);
@ -372,9 +376,10 @@ void PreRender_FetchFbufCoverage(PreRender* this, Gfx** gfxp) {
// FORCE_BL : Apply the blender to all pixels rather than just edges, skip the division step of the blend formula // FORCE_BL : Apply the blender to all pixels rather than just edges, skip the division step of the blend formula
// (G_BL_CLR_IN * G_BL_0 + G_BL_CLR_BL * G_BL_A_MEM) = G_BL_CLR_BL * G_BL_A_MEM // (G_BL_CLR_IN * G_BL_0 + G_BL_CLR_BL * G_BL_A_MEM) = G_BL_CLR_BL * G_BL_A_MEM
// //
// G_BL_A_MEM ("memory alpha") is coverage, therefore this blender configuration emits only the coverage (up to a // G_BL_A_MEM ("memory alpha") is coverage (shifted into the most significant 3 bits of the 5-bit blender alpha
// constant factor determined by blend color) and discards any pixel colors. For an RGBA16 framebuffer, each of the // input), therefore this blender configuration emits only the coverage (up to a constant factor determined by
// three color channels r,g,b will receive the coverage value individually. // blend color) and discards any pixel colors. For an RGBA16 framebuffer, each of the three color channels r,g,b
// will receive the coverage value individually.
// //
// Also disables other modes such as alpha compare and texture perspective correction // Also disables other modes such as alpha compare and texture perspective correction
gDPSetOtherMode(gfx++, gDPSetOtherMode(gfx++,