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LibSoftGPU: Check for bottom edge in top-left rule in Device

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If a triangle edge is completely horizontal and moving in a positive X
direction, we were erroneously treating it as a top edge. This adds
a better check that accounts for those edges. :^)
This commit is contained in:
Jelle Raaijmakers 2022-04-17 22:14:45 +02:00 • committed by Andreas Kling
parent 838cee37a2
commit e1a6966863
1 changed files with 5 additions and 6 deletions
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11
Userland/Libraries/LibSoftGPU/Device.cpp
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@ -213,16 +213,15 @@ void Device::rasterize_triangle(Triangle const& triangle)
// Zero is used in testing against edge values below, applying the "top-left rule". If a pixel // Zero is used in testing against edge values below, applying the "top-left rule". If a pixel
// lies exactly on an edge shared by two triangles, we only render that pixel if the edge in // lies exactly on an edge shared by two triangles, we only render that pixel if the edge in
// question is a "top" or "left" edge. We can detect those easily by testing for Y2 <= Y1, // question is a "top" or "left" edge. By changing a float epsilon to 0, we effectively change
// since we know our vertices are in CCW order. By changing a float epsilon to 0, we // the comparisons against the edge values below from "> 0" into ">= 0".
// effectively change the comparisons against the edge values below from "> 0" into ">= 0".
constexpr auto epsilon = NumericLimits<float>::epsilon(); constexpr auto epsilon = NumericLimits<float>::epsilon();
FloatVector3 zero { epsilon, epsilon, epsilon }; FloatVector3 zero { epsilon, epsilon, epsilon };
if (v2.y() <= v1.y()) if (v2.y() < v1.y() || (v2.y() == v1.y() && v2.x() < v1.x()))
zero.set_x(0.f); zero.set_x(0.f);
if (v0.y() <= v2.y()) if (v0.y() < v2.y() || (v0.y() == v2.y() && v0.x() < v2.x()))
zero.set_y(0.f); zero.set_y(0.f);
if (v1.y() <= v0.y()) if (v1.y() < v0.y() || (v1.y() == v0.y() && v1.x() < v0.x()))
zero.set_z(0.f); zero.set_z(0.f);
// This function tests whether a point as identified by its 3 edge values lies within the triangle // This function tests whether a point as identified by its 3 edge values lies within the triangle