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https://github.com/RGBCube/serenity
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220ac5eb02
The previous clipping implementation was problematic especially when clipping against the near plane. Triangles are now correctly clipped using homogenous coordinates against all frustum planes. Texture coordinates and vertex colors are now correctly interpolated. The earier implementation was just a placeholder.
83 lines
2.8 KiB
C++
83 lines
2.8 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 <LibGL/Clipper.h>
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namespace GL {
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bool Clipper::point_within_clip_plane(const FloatVector4& vertex, ClipPlane plane)
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{
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switch (plane) {
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case ClipPlane::LEFT:
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return vertex.x() > -vertex.w();
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case ClipPlane::RIGHT:
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return vertex.x() < vertex.w();
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case ClipPlane::TOP:
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return vertex.y() < vertex.w();
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case ClipPlane::BOTTOM:
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return vertex.y() > -vertex.w();
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case ClipPlane::NEAR:
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return vertex.z() > -vertex.w();
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case 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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GLVertex Clipper::clip_intersection_point(const GLVertex& p1, const GLVertex& p2, ClipPlane plane_index)
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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 Homogenous Coordinates" Blinn/Newell, 1978
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float w1 = p1.position.w();
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float w2 = p2.position.w();
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float x1 = clip_plane_normals[plane_index].dot(p1.position);
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float x2 = clip_plane_normals[plane_index].dot(p2.position);
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float a = (w1 + x1) / ((w1 + x1) - (w2 + x2));
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GLVertex out;
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out.position = p1.position * (1 - a) + p2.position * a;
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out.color = p1.color * (1 - a) + p2.color * a;
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out.tex_coord = p1.tex_coord * (1 - a) + p2.tex_coord * a;
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return out;
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}
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void Clipper::clip_triangle_against_frustum(Vector<GLVertex>& 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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auto read_from = &list_a;
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auto write_to = &list_b;
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for (size_t plane = 0; plane < NUMBER_OF_CLIPPING_PLANES; plane++) {
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write_to->clear_with_capacity();
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// Save me, C++23
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for (size_t i = 0; i < read_from->size(); i++) {
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const auto& curr_vec = read_from->at((i + 1) % read_from->size());
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const auto& prev_vec = read_from->at(i);
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if (point_within_clip_plane(curr_vec.position, static_cast<ClipPlane>(plane))) {
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if (!point_within_clip_plane(prev_vec.position, static_cast<ClipPlane>(plane))) {
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auto intersect = clip_intersection_point(prev_vec, curr_vec, static_cast<ClipPlane>(plane));
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write_to->append(intersect);
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}
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write_to->append(curr_vec);
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} else if (point_within_clip_plane(prev_vec.position, static_cast<ClipPlane>(plane))) {
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auto intersect = clip_intersection_point(prev_vec, curr_vec, static_cast<ClipPlane>(plane));
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write_to->append(intersect);
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}
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}
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swap(write_to, read_from);
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}
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input_verts = *read_from;
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}
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}
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