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LibSoftGPU: Take sample from pixel center

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This adds a half pixel offset to the edge value calculation in order to
sample the triangle at pixel centers. This is in line with actual OpenGL
rasterization rules and generates correctly interpolated vertex
attributes including texture coordinates.
This commit is contained in:
Stephan Unverwerth 2022-01-08 03:37:32 +01:00 • committed by Ali Mohammad Pur
parent 5028b53b49
commit d45931b423
1 changed files with 6 additions and 1 deletions
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7
Userland/Libraries/LibSoftGPU/Device.cpp
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@ -259,6 +259,11 @@ void Device::rasterize_triangle(const Triangle& triangle)
int const render_bounds_top = render_bounds.y();
int const render_bounds_bottom = render_bounds.y() + render_bounds.height();
auto const half_pixel_offset = Vector2<i32x4> {
expand4(subpixel_factor / 2),
expand4(subpixel_factor / 2),
};
// Iterate over all blocks within the bounds of the triangle
for (int by = by0; by < by1; by += 2) {
for (int bx = bx0; bx < bx1; bx += 2) {
@ -270,7 +275,7 @@ void Device::rasterize_triangle(const Triangle& triangle)
i32x4 { by, by, by + 1, by + 1 },
};
auto edge_values = calculate_edge_values4(quad.screen_coordinates * subpixel_factor);
auto edge_values = calculate_edge_values4(quad.screen_coordinates * subpixel_factor + half_pixel_offset);
// Generate triangle coverage mask
quad.mask = test_point4(edge_values);