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899f062673
The clipping logic is not DRY (Don't Repeat Yourself). The same logic is repeated in multiple parts of an `if-else` statement. This can be simplified to contain fewer branches and eliminate the redundant code.
100 lines
3.5 KiB
C++
100 lines
3.5 KiB
C++
/*
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* Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
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* Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Format.h>
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#include <AK/ScopeGuard.h>
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#include <LibSoftGPU/Clipper.h>
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namespace SoftGPU {
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static constexpr FloatVector4 clip_plane_normals[] = {
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{ 1, 0, 0, 0 }, // Left Plane
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{ -1, 0, 0, 0 }, // Right Plane
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{ 0, -1, 0, 0 }, // Top Plane
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{ 0, 1, 0, 0 }, // Bottom plane
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{ 0, 0, 1, 0 }, // Near Plane
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{ 0, 0, -1, 0 } // Far Plane
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};
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static constexpr bool point_within_clip_plane(FloatVector4 const& vertex, Clipper::ClipPlane plane)
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{
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switch (plane) {
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case Clipper::ClipPlane::LEFT:
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return vertex.x() >= -vertex.w();
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case Clipper::ClipPlane::RIGHT:
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return vertex.x() <= vertex.w();
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case Clipper::ClipPlane::TOP:
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return vertex.y() <= vertex.w();
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case Clipper::ClipPlane::BOTTOM:
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return vertex.y() >= -vertex.w();
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case Clipper::ClipPlane::NEAR:
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return vertex.z() >= -vertex.w();
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case Clipper::ClipPlane::FAR:
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return vertex.z() <= vertex.w();
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}
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return false;
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}
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static Vertex clip_intersection_point(Vertex const& p1, Vertex const& p2, Clipper::ClipPlane plane)
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{
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// See https://www.microsoft.com/en-us/research/wp-content/uploads/1978/01/p245-blinn.pdf
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// "Clipping Using Homogeneous Coordinates" Blinn/Newell, 1978
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float const w1 = p1.clip_coordinates.w();
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float const w2 = p2.clip_coordinates.w();
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float const x1 = clip_plane_normals[to_underlying(plane)].dot(p1.clip_coordinates);
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float const x2 = clip_plane_normals[to_underlying(plane)].dot(p2.clip_coordinates);
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float const a = (w1 + x1) / ((w1 + x1) - (w2 + x2));
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Vertex out;
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out.position = mix(p1.position, p2.position, a);
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out.eye_coordinates = mix(p1.eye_coordinates, p2.eye_coordinates, a);
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out.clip_coordinates = mix(p1.clip_coordinates, p2.clip_coordinates, a);
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out.color = mix(p1.color, p2.color, a);
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for (size_t i = 0; i < NUM_SAMPLERS; ++i)
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out.tex_coords[i] = mix(p1.tex_coords[i], p2.tex_coords[i], a);
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out.normal = mix(p1.normal, p2.normal, a);
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return out;
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}
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static void clip_plane(Vector<Vertex>& read_list, Vector<Vertex>& write_list, Clipper::ClipPlane plane)
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{
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auto read_from = &read_list;
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auto write_to = &write_list;
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write_to->clear_with_capacity();
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// FIXME C++23. Static reflection will provide looping over all enum values.
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for (size_t i = 0; i < read_from->size(); i++) {
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auto const& curr_vec = read_from->at((i + 1) % read_from->size());
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auto const& prev_vec = read_from->at(i);
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bool const is_curr_point_within_clip_plane = point_within_clip_plane(curr_vec.clip_coordinates, plane);
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bool const is_prev_point_within_clip_plane = point_within_clip_plane(prev_vec.clip_coordinates, plane);
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if (is_curr_point_within_clip_plane != is_prev_point_within_clip_plane) {
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auto const intersect = clip_intersection_point(prev_vec, curr_vec, plane);
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write_to->append(intersect);
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}
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if (is_curr_point_within_clip_plane)
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write_to->append(curr_vec);
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}
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swap(write_list, read_list);
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}
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void Clipper::clip_triangle_against_frustum(Vector<Vertex>& input_verts)
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{
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list_a = input_verts;
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list_b.clear_with_capacity();
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for (size_t plane = 0; plane < NUMBER_OF_CLIPPING_PLANES; plane++) {
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clip_plane(list_a, list_b, static_cast<ClipPlane>(plane));
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}
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input_verts = list_a;
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}
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}
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