From 4c9e16d5d4fb6f8ae1b826b9e5dd026f1bff39cc Mon Sep 17 00:00:00 2001 From: Jaklyy <102590697+Jaklyy@users.noreply.github.com> Date: Fri, 16 Aug 2024 20:35:11 -0400 Subject: [PATCH] rework polygon orientation calcs but this time actually correct --- src/GPU3D.cpp | 64 +++++++++++++++++++++++++++++---------------------- 1 file changed, 36 insertions(+), 28 deletions(-) diff --git a/src/GPU3D.cpp b/src/GPU3D.cpp index 865b00a1..ade5c417 100644 --- a/src/GPU3D.cpp +++ b/src/GPU3D.cpp @@ -965,50 +965,58 @@ void GPU3D::SubmitPolygon() noexcept VertexSlotCounter = 1; VertexSlotsFree = 0b11110; - // culling + // polygon orientation // TODO: work out how it works on the real thing // the normalization part is a wild guess - Vertex *v0, *v1, *v2, *v3; + Vertex *v0, *v1, *v2; s64 normalX, normalY, normalZ; s64 dot; + bool facingview; v0 = &TempVertexBuffer[0]; v1 = &TempVertexBuffer[1]; v2 = &TempVertexBuffer[2]; - v3 = &TempVertexBuffer[3]; - normalX = ((s64)(v0->Position[1]-v1->Position[1]) * (v2->Position[3]-v1->Position[3])) - - ((s64)(v0->Position[3]-v1->Position[3]) * (v2->Position[1]-v1->Position[1])); - normalY = ((s64)(v0->Position[3]-v1->Position[3]) * (v2->Position[0]-v1->Position[0])) - - ((s64)(v0->Position[0]-v1->Position[0]) * (v2->Position[3]-v1->Position[3])); - normalZ = ((s64)(v0->Position[0]-v1->Position[0]) * (v2->Position[1]-v1->Position[1])) - - ((s64)(v0->Position[1]-v1->Position[1]) * (v2->Position[0]-v1->Position[0])); - while ((((normalX>>31) ^ (normalX>>63)) != 0) || - (((normalY>>31) ^ (normalY>>63)) != 0) || - (((normalZ>>31) ^ (normalZ>>63)) != 0)) + // setup vectors for v0->v2 and v1->v2, with w serving as the z axis + s32 vector0[3] = { v0->Position[0] - v2->Position[0], v0->Position[1] - v2->Position[1], v0->Position[3] - v2->Position[3] }; + s32 vector1[3] = { v1->Position[0] - v2->Position[0], v1->Position[1] - v2->Position[1], v1->Position[3] - v2->Position[3] }; + + // if either vector is entirely 0, the polygon is accepted, and the front facing flag is set for the rasterizer + if (((vector0[0] | vector0[1] | vector0[2]) == 0) || ((vector1[0] | vector1[1] | vector1[2]) == 0)) { - normalX >>= 4; - normalY >>= 4; - normalZ >>= 4; + facingview = true; } - - dot = ((s64)v1->Position[0] * normalX) + ((s64)v1->Position[1] * normalY) + ((s64)v1->Position[3] * normalZ); - - bool facingview = (dot <= 0); - - if (dot < 0) + else { - if (!(CurPolygonAttr & (1<<7))) + // calculate cross product of the two vectors + normalX = ((s64)vector0[1] * vector1[2]) - ((s64)vector0[2] * vector1[1]); + normalY = ((s64)vector0[2] * vector1[0]) - ((s64)vector0[0] * vector1[2]); + normalZ = ((s64)vector0[0] * vector1[1]) - ((s64)vector0[1] * vector1[0]); + + // normalization (currently a guess) + while ((((normalX>>31) ^ (normalX>>63)) != 0) || + (((normalY>>31) ^ (normalY>>63)) != 0) || + (((normalZ>>31) ^ (normalZ>>63)) != 0)) { - LastStripPolygon = NULL; - return; + normalX >>= 4; + normalY >>= 4; + normalZ >>= 4; } - } - else if (dot > 0) - { - if (!(CurPolygonAttr & (1<<6))) + + // calculate dot product against the "camera vector" (we can use any of the vertices to do that) + dot = (v1->Position[0] * normalX) + (v1->Position[1] * normalY) + (v1->Position[3] * normalZ); + + // front facing flag is set for the rasterizer to be used for: + // unwinding vertices + // determining whether slopes should be treated as "swapped" + // and whether to overwrite a pixel with equal depth when using the < depth test + facingview = (dot >= 0); + + // cull polygon faces + if (!(((dot >= 0) && (CurPolygonAttr & (1<<7))) || // front facing + ((dot <= 0) && (CurPolygonAttr & (1<<6))))) // back facing { LastStripPolygon = NULL; return;