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LibGfx: Prevent out-of-bounds accumulation in PathRasterizer

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Negative accumulation on the right-hand side of the accumulation bitmap
would wrap around to the left, causing a negative start for certain
lines which resulted in horizontal streaks of lower alpha values.
Prevent this by not writing out of bounds :^)

Fixes #18394
This commit is contained in:
Jelle Raaijmakers 2023-04-18 23:55:57 +02:00 • committed by Andreas Kling
parent 8dc55f5fda
commit 0e8ef1b886
1 changed files with 2 additions and 1 deletions
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3
Userland/Libraries/LibGfx/Font/PathRasterizer.cpp
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@ -102,7 +102,8 @@ void PathRasterizer::draw_line(Gfx::FloatPoint p0, Gfx::FloatPoint p1)
// If x0 and x1 are within the same pixel, then area to the right is (1 - (mid(x0, x1) - x0_floor)) * dy
float area = .5f * (x0 + x1) - x0_floor;
m_data[line_offset + x0_floor_i] += directed_dy * (1.f - area);
m_data[line_offset + x0_floor_i + 1] += directed_dy * area;
if (x0_floor_i + 1 < static_cast<u32>(m_size.width()))
m_data[line_offset + x0_floor_i + 1] += directed_dy * area;
} else {
float x0_right = 1.f - (x0 - x0_floor);
u32 x1_floor_i = floorf(x1);