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/*
* Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
* Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Format.h>
#include <AK/ScopeGuard.h>
#include <LibGL/Clipper.h>
namespace GL {
bool Clipper::point_within_clip_plane(const FloatVector4& vertex, ClipPlane plane)
{
switch (plane) {
case ClipPlane::LEFT:
return vertex.x() > -vertex.w();
case ClipPlane::RIGHT:
return vertex.x() < vertex.w();
case ClipPlane::TOP:
return vertex.y() < vertex.w();
case ClipPlane::BOTTOM:
return vertex.y() > -vertex.w();
case ClipPlane::NEAR:
return vertex.z() > -vertex.w();
case ClipPlane::FAR:
return vertex.z() < vertex.w();
}
return false;
}
GLVertex Clipper::clip_intersection_point(const GLVertex& p1, const GLVertex& p2, ClipPlane plane_index)
{
// See https://www.microsoft.com/en-us/research/wp-content/uploads/1978/01/p245-blinn.pdf
// "Clipping Using Homogeneous Coordinates" Blinn/Newell, 1978
float w1 = p1.position.w();
float w2 = p2.position.w();
float x1 = clip_plane_normals[plane_index].dot(p1.position);
float x2 = clip_plane_normals[plane_index].dot(p2.position);
float a = (w1 + x1) / ((w1 + x1) - (w2 + x2));
GLVertex out;
out.position = p1.position * (1 - a) + p2.position * a;
out.color = p1.color * (1 - a) + p2.color * a;
out.tex_coord = p1.tex_coord * (1 - a) + p2.tex_coord * a;
return out;
}
void Clipper::clip_triangle_against_frustum(Vector<GLVertex>& input_verts)
{
list_a = input_verts;
list_b.clear_with_capacity();
auto read_from = &list_a;
auto write_to = &list_b;
for (size_t plane = 0; plane < NUMBER_OF_CLIPPING_PLANES; plane++) {
write_to->clear_with_capacity();
// Save me, C++23
for (size_t i = 0; i < read_from->size(); i++) {
const auto& curr_vec = read_from->at((i + 1) % read_from->size());
const auto& prev_vec = read_from->at(i);
if (point_within_clip_plane(curr_vec.position, static_cast<ClipPlane>(plane))) {
if (!point_within_clip_plane(prev_vec.position, static_cast<ClipPlane>(plane))) {
auto intersect = clip_intersection_point(prev_vec, curr_vec, static_cast<ClipPlane>(plane));
write_to->append(intersect);
}
write_to->append(curr_vec);
} else if (point_within_clip_plane(prev_vec.position, static_cast<ClipPlane>(plane))) {
auto intersect = clip_intersection_point(prev_vec, curr_vec, static_cast<ClipPlane>(plane));
write_to->append(intersect);
}
}
swap(write_to, read_from);
}
input_verts = *read_from;
}
}
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