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Insight: Shadowing is a visibility problem like the one for rendering in general.

• Render scene from the position of the light source into an off-screen depth buffer
• Render scene from the camera view. For every pixel: Compute position w.r.t. view from light source. Look up depth value from off-screen depth buffer. If , the pixel is in shadow.

Problem: Discretization of off-screen depth buffer leads to aliasing artifacts. The size of one texel of the shadow map in the final camera image is given by the following approximation:

: shadow map resolution
: distance from light source to shadow surface (affects Perspective Aliasing)
: angle between shadow surface and shadow map projection plane normal (affects Projective Aliasing)
: angle between shadow surface and image plane normal (affects Projective Aliasing)
: distance from shadow surface to camera (affects Perspective Aliasing)

can be decreased at the cost of memory / computation
can not be changed.

Goal: make as large as possible.

Solution: Apply the frustum transform of the camera to the scene before shadow map rendering and lookup. This effectively moves the camera center to infinity and thus minimizes the Perspective Aliasing caused by the camera distance.