culling.cpp

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/* Copyright (c) 2014-2017, ARM Limited and Contributors
 *
 * SPDX-License-Identifier: MIT
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 * to any person obtaining a copy of this software and associated documentation files (the "Software"),
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 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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#include "culling.hpp"

void CullingInterface::compute_frustum_from_view_projection(vec4 *planes, const mat4 &view_projection)
{
    mat4 inv_view_proj = mat_inverse(view_projection);

    // Get world-space coordinates for clip-space bounds.
    vec4 lbn = inv_view_proj * vec4(-1, -1, -1, 1);
    vec4 ltn = inv_view_proj * vec4(-1, 1, -1, 1);
    vec4 lbf = inv_view_proj * vec4(-1, -1, 1, 1);
    vec4 rbn = inv_view_proj * vec4( 1, -1, -1, 1);
    vec4 rtn = inv_view_proj * vec4( 1, 1, -1, 1);
    vec4 rbf = inv_view_proj * vec4( 1, -1, 1, 1);
    vec4 rtf = inv_view_proj * vec4( 1, 1, 1, 1);

    vec3 lbn_pos = vec_project(lbn);
    vec3 ltn_pos = vec_project(ltn);
    vec3 lbf_pos = vec_project(lbf);
    vec3 rbn_pos = vec_project(rbn);
    vec3 rtn_pos = vec_project(rtn);
    vec3 rbf_pos = vec_project(rbf);
    vec3 rtf_pos = vec_project(rtf);

    // Get plane equations for all sides of frustum.
    vec3 left_normal = vec_normalize(vec_cross(lbf_pos - lbn_pos, ltn_pos - lbn_pos));
    vec3 right_normal = vec_normalize(vec_cross(rtn_pos - rbn_pos, rbf_pos - rbn_pos));
    vec3 top_normal = vec_normalize(vec_cross(ltn_pos - rtn_pos, rtf_pos - rtn_pos));
    vec3 bottom_normal = vec_normalize(vec_cross(rbf_pos - rbn_pos, lbn_pos - rbn_pos));
    vec3 near_normal = vec_normalize(vec_cross(ltn_pos - lbn_pos, rbn_pos - lbn_pos));
    vec3 far_normal = vec_normalize(vec_cross(rtf_pos - rbf_pos, lbf_pos - rbf_pos));

    planes[0] = vec4(left_normal, -vec_dot(left_normal, lbn_pos)); // Left
    planes[1] = vec4(right_normal, -vec_dot(right_normal, rbn_pos)); // Right
    planes[2] = vec4(near_normal, -vec_dot(near_normal, lbn_pos)); // Near
    planes[3] = vec4(far_normal, -vec_dot(far_normal, lbf_pos)); // Far
    planes[4] = vec4(top_normal, -vec_dot(top_normal, ltn_pos)); // Top
    planes[5] = vec4(bottom_normal, -vec_dot(bottom_normal, lbn_pos)); // Bottom
}