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LibSoftGPU: Optimize clipping code

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Three optimizations are applied:

1. If the list of vertices to clip is empty, return immediately after
   clearing the output list.

2. Remember the previous vertex instead of recalculating whether it is
   within the clip plane.

3. Instead of copying and swapping lists around, operate on the input
   and output lists directly. This prevents a lot of `malloc`/`free`
   traffic as a result of vector assignments.

This takes the clipping code CPU load from 3.9% down to 1.8% for
Quake 3 on my machine.
This commit is contained in:
Jelle Raaijmakers 2022-04-10 02:50:26 +02:00 • committed by Brian Gianforcaro
parent 60fccdbd71
commit 4c1d8a7785
2 changed files with 25 additions and 28 deletions
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50
Userland/Libraries/LibSoftGPU/Clipper.cpp
View file

@ -65,43 +65,41 @@ static constexpr GPU::Vertex clip_intersection_point(GPU::Vertex const& p1, GPU:
}
template<Clipper::ClipPlane plane>
FLATTEN static constexpr void clip_plane(Vector<GPU::Vertex>& read_list, Vector<GPU::Vertex>& write_list)
FLATTEN static constexpr void clip_plane(Vector<GPU::Vertex>& input_list, Vector<GPU::Vertex>& output_list)
{
auto read_from = &read_list;
auto write_to = &write_list;
output_list.clear_with_capacity();
write_to->clear_with_capacity();
for (size_t i = 0; i < read_from->size(); i++) {
auto const& curr_vec = read_from->at((i + 1) % read_from->size());
auto const& prev_vec = read_from->at(i);
auto input_list_size = input_list.size();
if (input_list_size == 0)
return;
bool const is_curr_point_within_clip_plane = point_within_clip_plane<plane>(curr_vec.clip_coordinates);
bool const is_prev_point_within_clip_plane = point_within_clip_plane<plane>(prev_vec.clip_coordinates);
if (is_curr_point_within_clip_plane != is_prev_point_within_clip_plane) {
auto const intersect = clip_intersection_point<plane>(prev_vec, curr_vec);
write_to->append(intersect);
}
auto const* prev_vec = &input_list.data()[0];
auto is_prev_point_within_clip_plane = point_within_clip_plane<plane>(prev_vec->clip_coordinates);
for (size_t i = 1; i <= input_list_size; i++) {
auto const& curr_vec = input_list[i % input_list_size];
auto const is_curr_point_within_clip_plane = point_within_clip_plane<plane>(curr_vec.clip_coordinates);
if (is_curr_point_within_clip_plane != is_prev_point_within_clip_plane)
output_list.append(clip_intersection_point<plane>(*prev_vec, curr_vec));
if (is_curr_point_within_clip_plane)
write_to->append(curr_vec);
output_list.append(curr_vec);
prev_vec = &curr_vec;
is_prev_point_within_clip_plane = is_curr_point_within_clip_plane;
}
swap(write_list, read_list);
}
void Clipper::clip_triangle_against_frustum(Vector<GPU::Vertex>& input_verts)
{
list_a = input_verts;
list_b.clear_with_capacity();
// FIXME C++23. Static reflection will provide looping over all enum values.
clip_plane<ClipPlane::LEFT>(list_a, list_b);
clip_plane<ClipPlane::RIGHT>(list_a, list_b);
clip_plane<ClipPlane::TOP>(list_a, list_b);
clip_plane<ClipPlane::BOTTOM>(list_a, list_b);
clip_plane<ClipPlane::NEAR>(list_a, list_b);
clip_plane<ClipPlane::FAR>(list_a, list_b);
input_verts = list_a;
clip_plane<ClipPlane::LEFT>(input_verts, m_vertex_buffer);
clip_plane<ClipPlane::RIGHT>(m_vertex_buffer, input_verts);
clip_plane<ClipPlane::TOP>(input_verts, m_vertex_buffer);
clip_plane<ClipPlane::BOTTOM>(m_vertex_buffer, input_verts);
clip_plane<ClipPlane::NEAR>(input_verts, m_vertex_buffer);
clip_plane<ClipPlane::FAR>(m_vertex_buffer, input_verts);
}
}

3
Userland/Libraries/LibSoftGPU/Clipper.h
View file

@ -29,8 +29,7 @@ public:
void clip_triangle_against_frustum(Vector<GPU::Vertex>& input_vecs);
private:
Vector<GPU::Vertex> list_a;
Vector<GPU::Vertex> list_b;
Vector<GPU::Vertex> m_vertex_buffer;
};
}