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LibSoftGPU: Implement depth offset factor

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This implements the depth offset factor that you can set through e.g.
OpenGL's `glPolygonOffset`. Without it, triangles might start to Z-
fight amongst each other.

This fixes the floor decals in Quake 3.
This commit is contained in:
Jelle Raaijmakers 2022-05-10 01:32:04 +02:00 • committed by Andreas Kling
parent 62d41d58d6
commit b8c0ebccfd
1 changed files with 37 additions and 5 deletions
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42
Userland/Libraries/LibSoftGPU/Device.cpp
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@ -336,9 +336,6 @@ ALWAYS_INLINE void Device::rasterize(Gfx::IntRect& render_bounds, CB1 set_covera
};
if (m_options.enable_depth_test) {
set_quad_depth(quad);
// FIXME: Also apply depth_offset_factor which depends on the depth gradient
if (m_options.depth_offset_enabled)
quad.depth += m_options.depth_offset_constant * NumericLimits<float>::epsilon();
auto depth = load4_masked(depth_ptrs[0], depth_ptrs[1], depth_ptrs[2], depth_ptrs[3], quad.mask);
i32x4 depth_test_passed;
@ -742,6 +739,41 @@ void Device::rasterize_triangle(Triangle& triangle)
expand4(vertex2.window_coordinates.w()),
};
// Calculate depth offset to apply
float depth_offset = 0.f;
if (m_options.depth_offset_enabled) {
// Edge value deltas
auto edge_value_step_x = FloatVector3 {
static_cast<float>(v1.y() - v2.y()),
static_cast<float>(v2.y() - v0.y()),
static_cast<float>(v0.y() - v1.y()),
};
auto edge_value_step_y = FloatVector3 {
static_cast<float>(v2.x() - v1.x()),
static_cast<float>(v0.x() - v2.x()),
static_cast<float>(v1.x() - v0.x()),
};
// Barycentric deltas
auto barycentric_step_x = edge_value_step_x * one_over_area;
auto barycentric_step_y = edge_value_step_y * one_over_area;
// Depth delta vector and slope (magnitude)
auto depth_coordinates = FloatVector3 {
vertex0.window_coordinates.z(),
vertex1.window_coordinates.z(),
vertex2.window_coordinates.z(),
};
auto depth_step = FloatVector2 {
depth_coordinates.dot(barycentric_step_x),
depth_coordinates.dot(barycentric_step_y),
};
auto depth_max_slope = depth_step.length();
// Calculate total depth offset
depth_offset = depth_max_slope * m_options.depth_offset_factor + NumericLimits<float>::epsilon() * m_options.depth_offset_constant;
}
rasterize(
render_bounds,
[&](auto& quad) {
@ -754,12 +786,12 @@ void Device::rasterize_triangle(Triangle& triangle)
to_f32x4(edge_values.z()),
};
},
[&one_over_area, &window_z_coordinates](auto& quad) {
[&](auto& quad) {
// Determine each edge's ratio to the total area
quad.barycentrics = quad.barycentrics * one_over_area;
// Because the Z coordinates were divided by W, we can interpolate between them
quad.depth = window_z_coordinates.dot(quad.barycentrics);
quad.depth = window_z_coordinates.dot(quad.barycentrics) + depth_offset;
},
[&](auto& quad) {
auto const interpolated_reciprocal_w = window_w_coordinates.dot(quad.barycentrics);