I am doing cascaded shadowmapping and having some issues.

I have a scene like this (yellow light is from a point light; theres also a chair just outside the view to the left):

[attachment=26364:1.png]

If do not use a lights view matrix at all, i.e I only use an orthographic projection matrix when rendering shadow maps, it looks OK. The cascade order is top left, top right, bottom left, bottom right.

[attachment=26365:asd.png]

Now if I use an orthographic projection matrix and use a rotation matrix (as in the code below) based on the lights direction, it instead looks like this:

[attachment=26366:asd2.png]

Which is not correct, for example, the boxes are completely missing, even though they are encompassed in the orthographic projection

The resulting shadows then look like this:

[attachment=26369:asd3.png]

Some parts of shadow are correct, but major artifacts.

Here's how I build the matrix:

Mat4 CreateDirLightVPMatrix(const CameraFrustrum& cameraFrustrum, const Vec3& lightDir /* == Vec3(-1.0f, -1.0f, -1.0f) in this example */)
{
	// "cameraFrustrum" contains the 8 corners of the cameras frustrum in world space
	float maxZ = cameraFrustrum[0].z, minZ = cameraFrustrum[0].z;
	float maxX = cameraFrustrum[0].x, minX = cameraFrustrum[0].x;
	float maxY = cameraFrustrum[0].y, minY = cameraFrustrum[0].y;
	for (uint32_t i = 1; i < 8; i++)
	{
		if (cameraFrustrum[i].z > maxZ) maxZ = cameraFrustrum[i].z;
		if (cameraFrustrum[i].z < minZ) minZ = cameraFrustrum[i].z;
		if (cameraFrustrum[i].x > maxX) maxX = cameraFrustrum[i].x;
		if (cameraFrustrum[i].x < minX) minX = cameraFrustrum[i].x;
		if (cameraFrustrum[i].y > maxY) maxY = cameraFrustrum[i].y;
		if (cameraFrustrum[i].y < minY) minY = cameraFrustrum[i].y;
	}

	Vec3 right = glm::normalize(glm::cross(glm::normalize(lightDir), Vec3(0.0f, 1.0f, 0.0f)));
	Vec3 up = glm::normalize(glm::cross(glm::normalize(lightDir), right));

	Mat4 lightViewMatrix = Mat4(Vec4(right, 0.0f),
								Vec4(-up, 0.0f),		// why do I need to negate this btw?
								Vec4(lightDir, 0.0f),
								Vec4(0.0f, 0.0f, 0.0f, 1.0f));

	return OrthographicMatrix(minX, maxX, maxY, minY, maxZ, minZ) * lightViewMatrix;
}

It was my understanding (based on topics like https://www.opengl.org/discussion_boards/showthread.php/155674-Shadow-maps-for-infinite-light-sources), that all I needed to do shadow mapping for directional light was an orthographic projection matrix and then a rotation matrix (with no translation component, since the dir light has no position, and as I've understod it, translation dosnt matter since it is orthographic meaning no perspective anyway).

Then what is causing the errors in the 3rd image? Is there something I am missing?

Which is not correct, for example, the boxes are completely missing, even though they are encompassed in the orthographic projection

So how are you culling them?


L. Spiro

Not sure I follow; they are in the bounds of the orthographic matrix (as seen in the 2nd image) so why are they not visible after I apply the rotation matrix?

If you want your camera to move past it's original position, then you'll need a light matrix to do a transform.

What has this got to do with the (scene) camera? Or do you mean the camera as in the lights view? If so, my understanding of orthographic projection was that I didn't need to translate the camera at all

The directional light has no position, but your orthographic projection still needs to know where it's pointing at and what it's bounds are.

"Where its pointing at" - defined by the rotation matrix? "What its bounds are" - defined by the orthographic projection matrix, built from the max/min of the camera frustrum corners? Is there anything I'm missing?

so why are they not visible after I apply the rotation matrix?

I guess that was my point.
Why isn’t it visible? How are you culling it? How are you drawing it?
Are you sure it is in view? Because if so, and you actually sent valid commands to draw it, it would be there with the rest of the objects.


L. Spiro

I'm positive the problem is related to the projection and/or lights view matrix. Is there anything I'm missing when building the lights projection/view matrix? It is true the view matrix needs no translation at all and just the rotation as in my code above?

It is true the view matrix needs no translation at all and just the rotation as in my code above?

False. The projection determines the size and shape of a frustum "box." That box has no direct relationship to world coordinates. The view matrix determines the position and orientation of objects that will (eventually) be included/excluded from the frustum volume. Thinking in sort a backwards sense, the view matrix "positions" the frustum volume in the world, and objects which are not in the volume don't get rendered.

That makes sense!

So, if I already have the world position of the box, how do I build a view matrix that dosn't change the position, only the orientation of the objects?

I.e, I have the world space corners of the camera frustrum, that will build the ortho box. I want the objects in it, but viewed from a certain direction, how do I build such a matrix?