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lecture02

# lecture02 - 30 blockage ● Could trace a conical beam from...

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David Luebke 1 12/09/11 CS 551/651: Advanced Computer Graphics Ray Tracing Continued

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David Luebke 2 12/09/11 Basic Algorithm: Code Color TraceRay (Ray R ) if rayHitsObjects ( R ) then Color localC , reflectC , refractC ; Object O = findNearestObject ( R ); localC = shade ( O , R ); // shadow rays? Ray reflectedRay = calcReflect ( O , R ) Ray refractedRay = calcRefract ( O , R ) reflectC = TraceRay ( reflectedRay ); refractC = TraceRay ( refractedRay ); return localC reflectC refractC else return backgroundColor
David Luebke 3 12/09/11 Shadow Ray Problems: Sharp Shadows Why are the shadows sharp? A: Infinitely small point light sources What can we do about it? A: Implement area light sources How?

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David Luebke 4 12/09/11 Shadow Ray Problems:

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Unformatted text preview: 30% blockage ● Could trace a conical beam from point of intersection to light source: ● Track portion of beam blocked by occluding polygons: David Luebke 5 Shadow Ray Problems: Area Light Sources ● Too hard! Approximate instead: ● Sample the light source over its area and take weighted average: 50% blockage David Luebke 6 Shadow Ray Problems: Area Light Sources ● Disadvantages: ■ Less accurate (50% vs. 30% blockage) ■ Oops! Just quadrupled (at least) number of shadow rays ● Moral of the story: ■ Soft shadows are very expensive in ray tracing David Luebke 7 The End...
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lecture02 - 30 blockage ● Could trace a conical beam from...

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