Course Note Credit: Some of slides are extracted from the course notes of prof. Mathieu Desburn (USC) and prof. Han-Wei Shen (Ohio State University). CSC 830 Computer Graphics Lecture 7 Shadow & more

Shadow increases realism and depth cue

Shadows as Depth cue

Shadow and Arts

Duality of shadow & view

Shadow Ray

Shadow Maps

Shadow map look up

Shadow maps - renderman

Shadow maps

Shadow map problems? Field of view

Shadow map problems? Bias

Term project from year 2003 – Son & Mayuresh Zero Error Compensation Some Error Compensation

Term project from year 2003 – Son & Mayuresh Choosing the good error value : Trial And Error Method. Optimum Error CompensationToo Much Error Compensation

Shadow map problems? Aliasing

Shadow map filtering

Percentage closer filtering

Shadows in production

Fake shadows using textures

Projective Texture Projective texture mapping is a technique for generating texture coordinates dynamically via a projection of 3D geometry into a (usually 2D) texture map. In the same way that screen coordinates are generated by projecting 3D geometry onto your 2D screen, 3D geometry can be projected onto a texture map. This is done by using an appropriately-formed projective texture matrix. the textures are often re-generated each frame by rendering into the texture map which is subsequently projected onto the scene geometry. Figure 1. Two different views of a smiley face texture projected onto the scene.

Similar to Shadow map Pass I: Compute shadow map from light source Store Z - value of each pixel in the shadow map/Light map. Pass II : Shadow map : Look up the shadow map to know if points are in shadow by checking z < Z. Slide Projection : Look up the light map (projection slide) to know if the points are in the surface that is lit by the projector. And then modulate color of each pixel to simulate the effect of slide projector.

Projective Texture or Perspective correct Texture? (a) projective space interpolation (b) screen space interpolation Figure 2. These images illustrate interpolation in (a) projective space and (b) real space.

Accumulation Buffer motion blurr antialiasing soft shadow depth of field

For the case of a light source positioned infinitely far away, we will assume that all the rays reaching the object are parallel. This will allow us to solve the shadow equations once, and apply the solutions to every vertex in our object. Given 2 points: light point, vertex point, We want to calculate: shadow point, Check Check Check