113 lines
4.8 KiB
C
113 lines
4.8 KiB
C
#include "frustum.h"
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#include "_internal/private_frustum.h"
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#include <math.h>
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#include <stdint.h>
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/**
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* Extracts the six clipping planes from a combined View-Projection matrix.
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* * This function utilizes the Gribb-Hartmann method to derive plane equations
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* directly from the matrix rows. The resulting planes are normalized to ensure
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* that the distance calculations in visibility tests are accurate.
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*/
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void extract_frustum_planes(frustum_plane_struct planes[number_of_planes],
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Matrix view_projection)
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{
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/* Left Clipping Plane */
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planes[left].normal.x = view_projection.m3 + view_projection.m0;
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planes[left].normal.y = view_projection.m7 + view_projection.m4;
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planes[left].normal.z = view_projection.m11 + view_projection.m8;
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planes[left].distance = view_projection.m15 + view_projection.m12;
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/* Right Clipping Plane */
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planes[right].normal.x = view_projection.m3 - view_projection.m0;
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planes[right].normal.y = view_projection.m7 - view_projection.m4;
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planes[right].normal.z = view_projection.m11 - view_projection.m8;
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planes[right].distance = view_projection.m15 - view_projection.m12;
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/* Bottom Clipping Plane */
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planes[bottom].normal.x = view_projection.m3 + view_projection.m1;
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planes[bottom].normal.y = view_projection.m7 + view_projection.m5;
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planes[bottom].normal.z = view_projection.m11 + view_projection.m9;
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planes[bottom].distance = view_projection.m15 + view_projection.m13;
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/* Top Clipping Plane */
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planes[top].normal.x = view_projection.m3 - view_projection.m1;
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planes[top].normal.y = view_projection.m7 - view_projection.m5;
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planes[top].normal.z = view_projection.m11 - view_projection.m9;
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planes[top].distance = view_projection.m15 - view_projection.m13;
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/* Near Clipping Plane */
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planes[near].normal.x = view_projection.m3 + view_projection.m2;
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planes[near].normal.y = view_projection.m7 + view_projection.m6;
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planes[near].normal.z = view_projection.m11 + view_projection.m10;
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planes[near].distance = view_projection.m15 + view_projection.m14;
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/* Far Clipping Plane */
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planes[far].normal.x = view_projection.m3 - view_projection.m2;
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planes[far].normal.y = view_projection.m7 - view_projection.m6;
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planes[far].normal.z = view_projection.m11 - view_projection.m10;
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planes[far].distance = view_projection.m15 - view_projection.m14;
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/* Normalize all planes so that normal length equals 1.0 */
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for (uint8_t plane_index = 0; plane_index < number_of_planes; plane_index++)
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{
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float magnitude = sqrtf(
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planes[plane_index].normal.x * planes[plane_index].normal.x +
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planes[plane_index].normal.y * planes[plane_index].normal.y +
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planes[plane_index].normal.z * planes[plane_index].normal.z
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);
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if (magnitude > 0.0f)
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{
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float inverse_magnitude = 1.0f / magnitude;
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planes[plane_index].normal.x *= inverse_magnitude;
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planes[plane_index].normal.y *= inverse_magnitude;
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planes[plane_index].normal.z *= inverse_magnitude;
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planes[plane_index].distance *= inverse_magnitude;
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}
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}
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}
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/**
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* Checks if an Axis-Aligned Bounding Box (AABB) is within the view frustum.
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* * This function performs a fast visibility test by finding the "positive vertex"
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* of the box (the corner most aligned with the plane normal). If this vertex
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* is outside any of the six planes, the entire box is considered culled.
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*/
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bool is_axis_aligned_bounding_box_in_frustum( const frustum_plane_struct planes
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[
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number_of_planes
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],
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BoundingBox bounds)
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{
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for (uint8_t plane_index = 0; plane_index < number_of_planes; plane_index++)
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{
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Vector3 positive_vertex;
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positive_vertex.x =
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(planes[plane_index].normal.x >= 0.0f) ? bounds.max.x : bounds.min.x;
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positive_vertex.y =
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(planes[plane_index].normal.y >= 0.0f) ? bounds.max.y : bounds.min.y;
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positive_vertex.z =
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(planes[plane_index].normal.z >= 0.0f) ? bounds.max.z : bounds.min.z;
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/* Calculate the signed distance from the plane to the positive vertex */
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float vertex_distance =
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planes[plane_index].normal.x * positive_vertex.x +
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planes[plane_index].normal.y * positive_vertex.y +
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planes[plane_index].normal.z * positive_vertex.z +
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planes[plane_index].distance;
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/* If the most positive point is behind the plane, the box is outside the frustum */
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if (vertex_distance < 0.0f)
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{
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return false;
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}
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}
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return true;
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}
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