internal void PreDraw(int swapchainIndex, Float3 sunDirection, float shadowDistance)
{
//Get the 'normal' scene projections for current camera and aspect
CameraData sceneCameraData = CameraData.FromCamera(scene.Camera, swapchainAspect);
//Rotation from world to 'sun' direction
Float4x4 rotationMatrix = Float4x4.CreateRotationFromAxis(sunDirection, Float3.Forward);
//Calculate a sphere in 'lightspace' that fits the frustum of the camera
//using a sphere so that the size stays constant when the camera rotates, this avoids
//the shimmering when the shadow map is resized all the time
FloatSphere shadowSphere = GetShadowSphere(
sceneCameraData.InverseViewProjectionMatrix,
rotationMatrix.Invert(),
shadowDistance);
//Derive the projection values from the sphere
Float3 shadowCenter = shadowSphere.Center;
float radius = shadowSphere.Radius.Round();
float shadowSize = radius * 2f;
float shadowNearClip = -radius;
float shadowFarClip = radius;
//Calculate the matrices for the shadow projection
Float4x4 cameraMatrix = rotationMatrix * Float4x4.CreateTranslation(shadowCenter);
Float4x4 viewMatrix = cameraMatrix.Invert();
Float4x4 projectionMatrix = Float4x4.CreateOrthographicProjection(
shadowSize.XX(), shadowNearClip, shadowFarClip);
Float4x4 viewProjectionMatrix = projectionMatrix * viewMatrix;
//Calculate a rounding matrix to fix shadow 'shimmering' as objects constantly 'switch'
//between pixels in the shadowmap
float targetHalfSize = targetSize / 2f;
Float2 shadowOrigin = viewProjectionMatrix.TransformPoint((0f, 0f, 0f)).XY *targetHalfSize;
Float2 rounding = (shadowOrigin.Round() - shadowOrigin) / targetHalfSize;
Float4x4 roundingMat = Float4x4.CreateTranslation(rounding.XY0);
//Apply rounding
projectionMatrix = roundingMat * projectionMatrix;
viewProjectionMatrix = roundingMat * viewProjectionMatrix;
//Update shadow projection data in the buffer
cameraBuffer.Write(new CameraData(
cameraMatrix,
viewMatrix,
projectionMatrix,
viewProjectionMatrix,
viewProjectionMatrix.Invert(),
shadowNearClip,
shadowFarClip), offset: CameraData.SIZE * swapchainIndex);
}
