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LibSoftGPU: Use approximation for maximum depth slope
OpenGL allows GPUs to approximate a triangle's maximum depth slope which prevents a number computationally expensive instructions. On my machine, this gives me +6% FPS in Quake III. We are able to reuse `render_bounds` here since it is the containing rect of the (X, Y) window coordinates of the triangle, thus its width and height are the maximum delta X and delta Y, respectively.
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sideshowbarker
2024-07-17 07:21:04 +09:00
Author: https://github.com/gmta Commit: https://github.com/SerenityOS/serenity/commit/b42feb76a0 Pull-request: https://github.com/SerenityOS/serenity/pull/15165
@ -743,33 +743,13 @@ void Device::rasterize_triangle(Triangle& triangle)
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// Calculate depth offset to apply
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float depth_offset = 0.f;
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if (m_options.depth_offset_enabled) {
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// Edge value deltas
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auto edge_value_step_x = FloatVector3 {
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static_cast<float>(v1.y() - v2.y()),
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static_cast<float>(v2.y() - v0.y()),
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static_cast<float>(v0.y() - v1.y()),
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};
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auto edge_value_step_y = FloatVector3 {
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static_cast<float>(v2.x() - v1.x()),
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static_cast<float>(v0.x() - v2.x()),
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static_cast<float>(v1.x() - v0.x()),
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};
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// Barycentric deltas
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auto barycentric_step_x = edge_value_step_x * one_over_area;
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auto barycentric_step_y = edge_value_step_y * one_over_area;
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// Depth delta vector and slope (magnitude)
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auto depth_coordinates = FloatVector3 {
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vertex0.window_coordinates.z(),
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vertex1.window_coordinates.z(),
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vertex2.window_coordinates.z(),
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};
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auto depth_step = FloatVector2 {
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depth_coordinates.dot(barycentric_step_x),
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depth_coordinates.dot(barycentric_step_y),
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};
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auto depth_max_slope = depth_step.length();
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// OpenGL 2.0 § 3.5.5 allows us to approximate the maximum slope
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auto delta_z = max(
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max(
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abs(vertex0.window_coordinates.z() - vertex1.window_coordinates.z()),
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abs(vertex1.window_coordinates.z() - vertex2.window_coordinates.z())),
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abs(vertex2.window_coordinates.z() - vertex0.window_coordinates.z()));
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auto depth_max_slope = max(delta_z / render_bounds.width(), delta_z / render_bounds.height());
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// Calculate total depth offset
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depth_offset = depth_max_slope * m_options.depth_offset_factor + NumericLimits<float>::epsilon() * m_options.depth_offset_constant;
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