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- Handle degenerate triangles either sent as input or caused by clipping

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This commit is contained in:
Magnus Norddahl 2017-05-10 02:43:00 +02:00
commit f492e92cb5
3 changed files with 43 additions and 22 deletions
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32
src/polyrenderer/drawers/poly_triangle.cpp
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@ -152,8 +152,28 @@ ShadedTriVertex PolyTriangleDrawer::shade_vertex(const TriMatrix &objectToClip,
return sv;
}
bool PolyTriangleDrawer::is_degenerate(const ShadedTriVertex *vert)
{
// A degenerate triangle has a zero cross product for two of its sides.
float ax = vert[1].x - vert[0].x;
float ay = vert[1].y - vert[0].y;
float az = vert[1].w - vert[0].w;
float bx = vert[2].x - vert[0].x;
float by = vert[2].y - vert[0].y;
float bz = vert[2].w - vert[0].w;
float crossx = ay * bz - az * by;
float crossy = az * bx - ax * bz;
float crossz = ax * by - ay * bx;
float crosslengthsqr = crossx * crossx + crossy * crossy + crossz * crossz;
return crosslengthsqr <= 1.e-6f;
}
void PolyTriangleDrawer::draw_shaded_triangle(const ShadedTriVertex *vert, bool ccw, TriDrawTriangleArgs *args, WorkerThreadData *thread)
{
// Reject triangle if degenerate
if (is_degenerate(vert))
return;
// Cull, clip and generate additional vertices as needed
TriVertex clippedvert[max_additional_vertices];
int numclipvert = clipedge(vert, clippedvert);
@ -224,14 +244,13 @@ void PolyTriangleDrawer::draw_shaded_triangle(const ShadedTriVertex *vert, bool
// Draw screen triangles
if (ccw)
{
for (int i = numclipvert; i > 1; i--)
for (int i = numclipvert - 1; i > 1; i--)
{
args->v1 = &clippedvert[numclipvert - 1];
args->v2 = &clippedvert[i - 1];
args->v3 = &clippedvert[i - 2];
args->CalculateGradients();
ScreenTriangle::Draw(args, thread);
if (args->CalculateGradients())
ScreenTriangle::Draw(args, thread);
}
}
else
@ -241,9 +260,8 @@ void PolyTriangleDrawer::draw_shaded_triangle(const ShadedTriVertex *vert, bool
args->v1 = &clippedvert[0];
args->v2 = &clippedvert[i - 1];
args->v3 = &clippedvert[i];
args->CalculateGradients();
ScreenTriangle::Draw(args, thread);
if (args->CalculateGradients())
ScreenTriangle::Draw(args, thread);
}
}
}