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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
parent 7ad61a97ed
commit f492e92cb5
3 changed files with 43 additions and 22 deletions
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32
src/polyrenderer/drawers/poly_triangle.cpp
View file

@ -152,8 +152,28 @@ ShadedTriVertex PolyTriangleDrawer::shade_vertex(const TriMatrix &objectToClip,
return sv; 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) 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 // Cull, clip and generate additional vertices as needed
TriVertex clippedvert[max_additional_vertices]; TriVertex clippedvert[max_additional_vertices];
int numclipvert = clipedge(vert, clippedvert); int numclipvert = clipedge(vert, clippedvert);
@ -224,14 +244,13 @@ void PolyTriangleDrawer::draw_shaded_triangle(const ShadedTriVertex *vert, bool
// Draw screen triangles // Draw screen triangles
if (ccw) if (ccw)
{ {
for (int i = numclipvert; i > 1; i--) for (int i = numclipvert - 1; i > 1; i--)
{ {
args->v1 = &clippedvert[numclipvert - 1]; args->v1 = &clippedvert[numclipvert - 1];
args->v2 = &clippedvert[i - 1]; args->v2 = &clippedvert[i - 1];
args->v3 = &clippedvert[i - 2]; args->v3 = &clippedvert[i - 2];
args->CalculateGradients(); if (args->CalculateGradients())
ScreenTriangle::Draw(args, thread);
ScreenTriangle::Draw(args, thread);
} }
} }
else else
@ -241,9 +260,8 @@ void PolyTriangleDrawer::draw_shaded_triangle(const ShadedTriVertex *vert, bool
args->v1 = &clippedvert[0]; args->v1 = &clippedvert[0];
args->v2 = &clippedvert[i - 1]; args->v2 = &clippedvert[i - 1];
args->v3 = &clippedvert[i]; args->v3 = &clippedvert[i];
args->CalculateGradients(); if (args->CalculateGradients())
ScreenTriangle::Draw(args, thread);
ScreenTriangle::Draw(args, thread);
} }
} }
} }

1
src/polyrenderer/drawers/poly_triangle.h
View file

@ -47,6 +47,7 @@ private:
static ShadedTriVertex shade_vertex(const TriMatrix &objectToClip, const float *clipPlane, const TriVertex &v); static ShadedTriVertex shade_vertex(const TriMatrix &objectToClip, const float *clipPlane, const TriVertex &v);
static void draw_arrays(const PolyDrawArgs &args, WorkerThreadData *thread); static void draw_arrays(const PolyDrawArgs &args, WorkerThreadData *thread);
static void draw_shaded_triangle(const ShadedTriVertex *vertices, bool ccw, TriDrawTriangleArgs *args, WorkerThreadData *thread); static void draw_shaded_triangle(const ShadedTriVertex *vertices, bool ccw, TriDrawTriangleArgs *args, WorkerThreadData *thread);
static bool is_degenerate(const ShadedTriVertex *vertices);
static int clipedge(const ShadedTriVertex *verts, TriVertex *clippedvert); static int clipedge(const ShadedTriVertex *verts, TriVertex *clippedvert);

32
src/polyrenderer/drawers/screen_triangle.h
View file

@ -66,29 +66,31 @@ struct TriDrawTriangleArgs
ScreenTriangleStepVariables gradientX; ScreenTriangleStepVariables gradientX;
ScreenTriangleStepVariables gradientY; ScreenTriangleStepVariables gradientY;
void CalculateGradients() bool CalculateGradients()
{ {
gradientX.W = FindGradientX(v1->x, v1->y, v2->x, v2->y, v3->x, v3->y, v1->w, v2->w, v3->w); float bottomX = (v2->x - v3->x) * (v1->y - v3->y) - (v1->x - v3->x) * (v2->y - v3->y);
gradientY.W = FindGradientY(v1->x, v1->y, v2->x, v2->y, v3->x, v3->y, v1->w, v2->w, v3->w); float bottomY = (v1->x - v3->x) * (v2->y - v3->y) - (v2->x - v3->x) * (v1->y - v3->y);
gradientX.U = FindGradientX(v1->x, v1->y, v2->x, v2->y, v3->x, v3->y, v1->u * v1->w, v2->u * v2->w, v3->u * v3->w); if ((bottomX >= -FLT_EPSILON && bottomX <= FLT_EPSILON) || (bottomY >= -FLT_EPSILON && bottomY <= FLT_EPSILON))
gradientY.U = FindGradientY(v1->x, v1->y, v2->x, v2->y, v3->x, v3->y, v1->u * v1->w, v2->u * v2->w, v3->u * v3->w); return false;
gradientX.V = FindGradientX(v1->x, v1->y, v2->x, v2->y, v3->x, v3->y, v1->v * v1->w, v2->v * v2->w, v3->v * v3->w);
gradientY.V = FindGradientY(v1->x, v1->y, v2->x, v2->y, v3->x, v3->y, v1->v * v1->w, v2->v * v2->w, v3->v * v3->w); gradientX.W = FindGradientX(bottomX, v1->w, v2->w, v3->w);
gradientY.W = FindGradientY(bottomY, v1->w, v2->w, v3->w);
gradientX.U = FindGradientX(bottomX, v1->u * v1->w, v2->u * v2->w, v3->u * v3->w);
gradientY.U = FindGradientY(bottomY, v1->u * v1->w, v2->u * v2->w, v3->u * v3->w);
gradientX.V = FindGradientX(bottomX, v1->v * v1->w, v2->v * v2->w, v3->v * v3->w);
gradientY.V = FindGradientY(bottomY, v1->v * v1->w, v2->v * v2->w, v3->v * v3->w);
return true;
} }
private: private:
static float FindGradientX(float x0, float y0, float x1, float y1, float x2, float y2, float c0, float c1, float c2) float FindGradientX(float bottomX, float c0, float c1, float c2)
{ {
float top = (c1 - c2) * (y0 - y2) - (c0 - c2) * (y1 - y2); return ((c1 - c2) * (v1->y - v3->y) - (c0 - c2) * (v2->y - v3->y)) / bottomX;
float bottom = (x1 - x2) * (y0 - y2) - (x0 - x2) * (y1 - y2);
return top / bottom;
} }
static float FindGradientY(float x0, float y0, float x1, float y1, float x2, float y2, float c0, float c1, float c2) float FindGradientY(float bottomY, float c0, float c1, float c2)
{ {
float top = (c1 - c2) * (x0 - x2) - (c0 - c2) * (x1 - x2); return ((c1 - c2) * (v1->x - v3->x) - (c0 - c2) * (v2->x - v3->x)) / bottomY;
float bottom = (x0 - x2) * (y1 - y2) - (x1 - x2) * (y0 - y2);
return top / bottom;
} }
}; };