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bool frustumCullingTest(mat4 mvp, vec3 bmin, vec3 bmax);
struct Frustum
{
vec4 planes[6];
};
/**
* Extract Frustum Planes from MVP Matrix
*
* Based on "Fast Extraction of Viewing Frustum Planes from the World-
* View-Projection Matrix", by Gil Gribb and Klaus Hartmann.
* This procedure computes the planes of the frustum and normalizes
* them.
*/
void loadFrustum(out Frustum f, mat4 mvp)
{
for (int i = 0; i < 3; ++i)
{
for (int j = 0; j < 2; ++j)
{
f.planes[i*2+j].x = mtxGetElement(mvp, 0, 3) + (j == 0 ? mtxGetElement(mvp, 0, i) : -mtxGetElement(mvp, 0, i));
f.planes[i*2+j].y = mtxGetElement(mvp, 1, 3) + (j == 0 ? mtxGetElement(mvp, 1, i) : -mtxGetElement(mvp, 1, i));
f.planes[i*2+j].z = mtxGetElement(mvp, 2, 3) + (j == 0 ? mtxGetElement(mvp, 2, i) : -mtxGetElement(mvp, 2, i));
f.planes[i*2+j].w = mtxGetElement(mvp, 3, 3) + (j == 0 ? mtxGetElement(mvp, 3, i) : -mtxGetElement(mvp, 3, i));
f.planes[i*2+j]*= length(f.planes[i*2+j].xyz);
}
}
}
/**
* Negative Vertex of an AABB
*
* This procedure computes the negative vertex of an AABB
* given a normal.
* See the View Frustum Culling tutorial @ LightHouse3D.com
* http://www.lighthouse3d.com/tutorials/view-frustum-culling/geometric-approach-testing-boxes-ii/
*/
vec3 negativeVertex(vec3 bmin, vec3 bmax, vec3 n)
{
bvec3 b = greaterThan(n, vec3(0.0, 0.0, 0.0));
return mix(bmin, bmax, b);
}
/**
* Frustum-AABB Culling Test
*
* This procedure returns true if the AABB is either inside, or in
* intersection with the frustum, and false otherwise.
* The test is based on the View Frustum Culling tutorial @ LightHouse3D.com
* http://www.lighthouse3d.com/tutorials/view-frustum-culling/geometric-approach-testing-boxes-ii/
*/
bool frustumCullingTest(mat4 mvp, vec3 bmin, vec3 bmax)
{
float a = 1.0f;
Frustum f;
loadFrustum(f, mvp);
for (int i = 0; i < 6 && a >= 0.0f; ++i)
{
vec3 n = negativeVertex(bmin, bmax, f.planes[i].xyz);
a = dot(vec4(n, 1.0f), f.planes[i]);
}
return (a >= 0.0);
}
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