private static FloatSphere GetShadowSphere(
Float4x4 ndcToWorldMat,
Float4x4 worldToLightMat,
float shadowDistance)
{
//Frustum of the camera that will be covered by the shadow map in NDC space
//Note: this covers the entire screen but only to a certain depth
FloatBox shadowNDC = new FloatBox(
min: (-1f, -1f, 0f),
max: (1f, 1f, DepthUtils.LinearToDepth(
shadowDistance,
Camera.NEAR_CLIP_DISTANCE,
Camera.FAR_CLIP_DISTANCE)));
//Gather points of the frustum
Span <Float3> points = stackalloc Float3[8];
shadowNDC.GetPoints(points);
//Transform all the points to lightspace (ndc -> world -> lightspace)
Float3 center = Float3.Zero;
for (int i = 0; i < points.Length; i++)
{
points[i] = (worldToLightMat * ndcToWorldMat).TransformPoint(points[i]);
center = i == 0 ? points[i] : (center + points[i]);
}
center /= points.Length;
//The the longest diagonal of the frustum and base our sphere on that
float squareDiag1 = (points[0] - points[6]).SquareMagnitude;
float squareDiag2 = (points[2] - points[4]).SquareMagnitude;
float radius = FloatUtils.SquareRoot(FloatUtils.Max(squareDiag1, squareDiag2)) * .5f;
return(new FloatSphere(center, radius));
}