mirror of
https://github.com/RGBCube/serenity
synced 2025-10-31 07:22:45 +00:00
e8cd89a538
This code has also been optimised to be much more memory friendly by removing a _lot_ of extraneous copies. The result is that, when profiled, it's around 8x faster than the previous implementation. Co-Authored-By: Ali Mohammad Pur <ali.mpfard@gmail.com>
110 lines
4.3 KiB
C++
110 lines
4.3 KiB
C++
/*
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* Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
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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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bool GL::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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// TODO: This needs to interpolate color/UV data as well!
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FloatVector4 GL::Clipper::clip_intersection_point(const FloatVector4& vec, const FloatVector4& prev_vec, ClipPlane plane_index)
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{
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//
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// This is an implementation of the Cyrus-Beck algorithm to clip lines against a plane
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// using the triangle's line segment in parametric form.
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// In this case, we find that n . [P(t) - plane] == 0 if the point lies on
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// the boundary, which in this case is the clip plane. We then substitute
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// P(t)= P1 + (P2-P1)*t (where P2 is a point inside the clipping boundary, and P1 is,
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// in this case, the point that lies outside the boundary due to our implementation of Sutherland-Hogdman)
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// into P(t) to arrive at the equation:
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//
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// n · [P1 + ((P2 - P1) * t) - plane] = 0.
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// Substitude seg_length = P2 - P1 (length of line segment) and dist = P1 - plane (distance from P1 to plane)
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//
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// By rearranging, we now end up with
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//
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// n·[P1 + (seg_length * t) - plane] = 0
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// n·(dist) + n·(seg_length * t) = 0
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// n·(seg_length*t) = -n·(dist)
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// Therefore
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// t = (-n·(dist))/(n·seg_length)
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//
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// NOTE: n is the normal vector to the plane we are clipping against.
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//
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// Proof of algorithm found here
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// http://studymaterial.unipune.ac.in:8080/jspui/bitstream/123456789/4843/1/Cyrus_Beck_Algo.pdf
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// And here (slightly more intuitive with a better diagram)
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// https://www.csee.umbc.edu/~rheingan/435/pages/res/gen-5.Clipping-single-page-0.html
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FloatVector4 seg_length = vec - prev_vec; // P2 - P1
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FloatVector4 dist = prev_vec - clip_planes[plane_index]; // Distance from "out of bounds" vector to plane
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float plane_normal_line_segment_dot_product = clip_plane_normals[plane_index].dot(seg_length);
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float neg_plane_normal_dist_dot_procut = -clip_plane_normals[plane_index].dot(dist);
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float t = (plane_normal_line_segment_dot_product / neg_plane_normal_dist_dot_procut);
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// P(t) = P1 + (t * (P2 - P1))
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FloatVector4 lerped_vec = prev_vec + (seg_length * t);
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return lerped_vec;
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}
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// FIXME: Getting too close to zNear causes VERY serious artifacting. Should we cull the whole triangle??
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void GL::Clipper::clip_triangle_against_frustum(Vector<FloatVector4>& input_verts)
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{
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Vector<FloatVector4, 6> clipped_polygon;
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Vector<FloatVector4, 6> input = input_verts;
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Vector<FloatVector4, 6>* current = &clipped_polygon;
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Vector<FloatVector4, 6>* output_list = &input;
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ScopeGuard guard { [&] { input_verts = *output_list; } };
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for (u8 plane = 0; plane < NUMBER_OF_CLIPPING_PLANES; plane++) {
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swap(current, output_list);
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clipped_polygon.clear();
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if (current->size() == 0) {
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return;
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}
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// Save me, C++23
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for (size_t i = 0; i < current->size(); i++) {
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const auto& curr_vec = current->at(i);
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const auto& prev_vec = current->at((i - 1) % current->size());
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if (point_within_clip_plane(curr_vec, static_cast<ClipPlane>(plane))) {
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if (!point_within_clip_plane(prev_vec, static_cast<ClipPlane>(plane))) {
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FloatVector4 intersect = clip_intersection_point(prev_vec, curr_vec, static_cast<ClipPlane>(plane));
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clipped_polygon.append(intersect);
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}
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clipped_polygon.append(curr_vec);
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} else if (point_within_clip_plane(prev_vec, static_cast<ClipPlane>(plane))) {
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FloatVector4 intersect = clip_intersection_point(prev_vec, curr_vec, static_cast<ClipPlane>(plane));
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clipped_polygon.append(intersect);
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}
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}
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}
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}
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