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LibSoftGPU: Implement 5 bits of subpixel precision

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This snaps vertices to 1/32 of a pixel before rasterization resulting
in smoother movement and less floaty appearance of moving triangles.

This also reduces the severity of the artifacts in the glquake port.

5 bits should allow up to 1024x1024 render targets. Anything larger
needs a different implementation.
This commit is contained in:
Stephan Unverwerth 2021-12-30 18:40:20 +01:00 • committed by Andreas Kling
parent c00014fa54
commit 8ae3eb6c33
2 changed files with 15 additions and 12 deletions
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26
Userland/Libraries/LibSoftGPU/Device.cpp
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@ -130,10 +130,12 @@ static void rasterize_triangle(const RasterizerOptions& options, Gfx::Bitmap& re
Vertex const vertex1 = triangle.vertices[1];
Vertex const vertex2 = triangle.vertices[2];
constexpr int subpixel_factor = 1 << SUBPIXEL_BITS;
// Calculate area of the triangle for later tests
IntVector2 const v0 { static_cast<int>(vertex0.window_coordinates.x()), static_cast<int>(vertex0.window_coordinates.y()) };
IntVector2 const v1 { static_cast<int>(vertex1.window_coordinates.x()), static_cast<int>(vertex1.window_coordinates.y()) };
IntVector2 const v2 { static_cast<int>(vertex2.window_coordinates.x()), static_cast<int>(vertex2.window_coordinates.y()) };
IntVector2 const v0 { static_cast<int>(vertex0.window_coordinates.x() * subpixel_factor), static_cast<int>(vertex0.window_coordinates.y() * subpixel_factor) };
IntVector2 const v1 { static_cast<int>(vertex1.window_coordinates.x() * subpixel_factor), static_cast<int>(vertex1.window_coordinates.y() * subpixel_factor) };
IntVector2 const v2 { static_cast<int>(vertex2.window_coordinates.x() * subpixel_factor), static_cast<int>(vertex2.window_coordinates.y() * subpixel_factor) };
int area = edge_function(v0, v1, v2);
if (area == 0)
@ -204,12 +206,12 @@ static void rasterize_triangle(const RasterizerOptions& options, Gfx::Bitmap& re
auto render_bounds = render_target.rect();
if (options.scissor_enabled)
render_bounds.intersect(scissor_box_to_window_coordinates(options.scissor_box, render_target.rect()));
int const block_padding = RASTERIZER_BLOCK_SIZE - 1;
// clang-format off
int const bx0 = max(render_bounds.left(), min(min(v0.x(), v1.x()), v2.x())) / RASTERIZER_BLOCK_SIZE;
int const bx1 = (min(render_bounds.right(), max(max(v0.x(), v1.x()), v2.x())) + block_padding) / RASTERIZER_BLOCK_SIZE;
int const by0 = max(render_bounds.top(), min(min(v0.y(), v1.y()), v2.y())) / RASTERIZER_BLOCK_SIZE;
int const by1 = (min(render_bounds.bottom(), max(max(v0.y(), v1.y()), v2.y())) + block_padding) / RASTERIZER_BLOCK_SIZE;
int const bx0 = max(render_bounds.left(), min(min(v0.x(), v1.x()), v2.x()) / subpixel_factor) / RASTERIZER_BLOCK_SIZE;
int const bx1 = (min(render_bounds.right(), max(max(v0.x(), v1.x()), v2.x()) / subpixel_factor)) / RASTERIZER_BLOCK_SIZE + 1;
int const by0 = max(render_bounds.top(), min(min(v0.y(), v1.y()), v2.y()) / subpixel_factor) / RASTERIZER_BLOCK_SIZE;
int const by1 = (min(render_bounds.bottom(), max(max(v0.y(), v1.y()), v2.y()) / subpixel_factor)) / RASTERIZER_BLOCK_SIZE + 1;
// clang-format on
u8 pixel_mask[RASTERIZER_BLOCK_SIZE];
@ -231,10 +233,10 @@ static void rasterize_triangle(const RasterizerOptions& options, Gfx::Bitmap& re
// Edge values of the 4 block corners
// clang-format off
auto b0 = calculate_edge_values({ bx * RASTERIZER_BLOCK_SIZE, by * RASTERIZER_BLOCK_SIZE });
auto b1 = calculate_edge_values({ bx * RASTERIZER_BLOCK_SIZE + RASTERIZER_BLOCK_SIZE, by * RASTERIZER_BLOCK_SIZE });
auto b2 = calculate_edge_values({ bx * RASTERIZER_BLOCK_SIZE, by * RASTERIZER_BLOCK_SIZE + RASTERIZER_BLOCK_SIZE });
auto b3 = calculate_edge_values({ bx * RASTERIZER_BLOCK_SIZE + RASTERIZER_BLOCK_SIZE, by * RASTERIZER_BLOCK_SIZE + RASTERIZER_BLOCK_SIZE });
auto b0 = calculate_edge_values(IntVector2{ bx, by } * RASTERIZER_BLOCK_SIZE * subpixel_factor);
auto b1 = calculate_edge_values(IntVector2{ bx + 1, by } * RASTERIZER_BLOCK_SIZE * subpixel_factor);
auto b2 = calculate_edge_values(IntVector2{ bx, by + 1 } * RASTERIZER_BLOCK_SIZE * subpixel_factor);
auto b3 = calculate_edge_values(IntVector2{ bx + 1, by + 1 } * RASTERIZER_BLOCK_SIZE * subpixel_factor);
// clang-format on
// If the whole block is outside any of the triangle edges we can discard it completely