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Modestas Andrijauskas

CSM min and max calculation for orthogonal projection

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I have two ways to calculate min and max vectors, which are later used to create light's orthogonal projection. Lets name them A and B, so A looks like this:

// Calculate min and max vectors, using viewer's camera frustum slice centroid and radius
minOrtho.set(0, 0, 0, 1).assign(centroid).sub(frustumRadius, frustumRadius, -frustumRadius, 0);
maxOrtho.set(0, 0, 0, 1).assign(centroid).add(frustumRadius, frustumRadius, -frustumRadius, 0);
// Transform min and max vectors into light's eye space
Matrix4f.transform(lightTransforms[i].view, minOrtho, tmpVector);
Matrix4f.transform(lightTransforms[i].view, maxOrtho, tmpVector);

and B:

minOrtho.set(Float.MAX_VALUE, Float.MAX_VALUE, Float.MAX_VALUE, 1.0f);
maxOrtho.set(Float.MIN_VALUE, Float.MIN_VALUE, Float.MIN_VALUE, 1.0f);
// Transform viewer's frustum slice points into light's eye space, then find mins and maxes
for(int j=0; j<8; j++){
	Matrix4f.transform(lightTransforms[i].view, tmpCamera.frustum.points[j].xyzw(), tmpVector);
	if(tmpCamera.frustum.points[j].x < minOrtho.x)
		minOrtho.x = tmpCamera.frustum.points[j].x;
	if(tmpCamera.frustum.points[j].y < minOrtho.y)
		minOrtho.y = tmpCamera.frustum.points[j].y;
	if(tmpCamera.frustum.points[j].z < minOrtho.z)
		minOrtho.z = tmpCamera.frustum.points[j].z;

	if(tmpCamera.frustum.points[j].x > maxOrtho.x)
		maxOrtho.x = tmpCamera.frustum.points[j].x;
	if(tmpCamera.frustum.points[j].y > maxOrtho.y)
		maxOrtho.y = tmpCamera.frustum.points[j].y;
	if(tmpCamera.frustum.points[j].z > maxOrtho.z)
		maxOrtho.z = tmpCamera.frustum.points[j].z;

Now what gives me headache is that I can't understand one thing. When I was writing graphics engine I used A code because shadows looked much softer than using B, but now I'm rewriting my graphics engine (old one was static and now I'm writing object-oriented) from scratch and now B gives better results than A, but I can't understand why?


I think myself that calculating min and max by fitting frustum into sphere and using that sphere radius is better solution, than finding min and max using frustum points. Maybe I did a mistake in A technique?

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