MIT EECS 6.837: Understanding Shadows in Computer Graphics, Slides of Computer Science

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MIT EECS 6.837, Durand and Cutler

Real-Time

Shadows

Last Time? • The graphics pipeline • Clipping & rasterization of polygons • Visibility — the depth buffer (z-buffer)

Questions?

Today • Why are Shadows Important? • Shadows & Soft Shadows in Ray Tracing • Planar Shadows • Shadow Maps • Shadow Volumes

Shadows as a Depth Cue

For Intuition about Scene Lighting • Position of the light (e.g. sundial) • Hard shadows vs. soft shadows • Colored lights • Directional light vs. point light

Shadows • One shadow ray per

intersection per pointlight source no shadow rays one shadow ray

Soft Shadows •

Caused byextended lightsources

Umbra - source completelyoccluded - Penumbra - Source partially occluded - Fully lit Image removed due to copyright considerations.

Shadows in Ray Tracing •

Shoot ray from visible point to light source

If blocked, discard light contribution - Optimization? - Stop after first intersection (don’tworry about tmin) - Coherence: remember the previous occluder,and test that object first

Traditional Ray Tracing

Today • Why are Shadows Important? • Shadows & Soft Shadows in Ray Tracing • Planar Shadows • Shadow Maps • Shadow Volumes

Cast Shadows on Planar Surfaces • Draw the object primitives a second time,

projected to the ground plane

Today • Why are Shadows Important? • Shadows & Soft Shadows in Ray Tracing • Planar Shadows • Shadow Maps

• Texture Mapping – Shadow View Duality
  • Shadow Volumes

Texture Mapping • Don't have to represent everything with geometry