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52d6ae36cb
Most resources seem to suggest that points on the clip planes are also inside the frustum, e.g.: https://www.cubic.org/docs/3dclip.htm This seems to resolve some rendering issues in Grim Fandango in OpenGL mode where the screen remained black. This was because of quads being drawn with their vertex positions exactly on the clip planes.
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 Homogeneous 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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