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rework polygon orientation calcs 

but this time actually correct
This commit is contained in:
Jaklyy 2024-08-16 20:35:11 -04:00
parent f79eb72ca5
commit 4c9e16d5d4
1 changed files with 36 additions and 28 deletions
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52
src/GPU3D.cpp
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@ -965,26 +965,37 @@ 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]));
// 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))
{
facingview = true;
}
else
{
// 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))
@ -994,21 +1005,18 @@ void GPU3D::SubmitPolygon() noexcept
normalZ >>= 4;
}
dot = ((s64)v1->Position[0] * normalX) + ((s64)v1->Position[1] * normalY) + ((s64)v1->Position[3] * normalZ);
// 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);
bool facingview = (dot <= 0);
// 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);
if (dot < 0)
{
if (!(CurPolygonAttr & (1<<7)))
{
LastStripPolygon = NULL;
return;
}
}
else if (dot > 0)
{
if (!(CurPolygonAttr & (1<<6)))
// cull polygon faces
if (!(((dot >= 0) && (CurPolygonAttr & (1<<7))) || // front facing
((dot <= 0) && (CurPolygonAttr & (1<<6))))) // back facing
{
LastStripPolygon = NULL;
return;