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Dynamic Shadows and Lighting for Walkthrus of Large Models

Brandon Lloyd

COMP 258December 2002

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Why Are Shadows Important?

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Why Are Shadows Important?

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Shadow Maps

Eye Light

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Shadow Maps

• Advantages– Only one additional

render pass– Very easy to use

• Disadvantages– Aliasing problems– Resolution restricted to

available memory– Requires a user-set bias.

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Perspective Shadow Maps

• Better utilizes available samples by warping depth map

• Find the volume that can contribute shadows to the view

• Fit light frustum to the volume in camera’s post-perspective space

• Render depth map in camera’s post-perspective space.

Perspective

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Perspective Shadow Maps

Standard Shadow Map Perspective Shadow Map

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Perspective Shadow Maps

Standard Shadow Map Perspective Shadow Map

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Perspective Shadow Maps

Standard Shadow Maps Perspective Shadow Maps

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Benefits of Using Cg

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Benefits of Using Cg

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Shadow Volumes

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2 21

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• Extrude shadow frusta from occluder edges to infinity

• Count crossings from eye to a point: – Front faces: +1– Back faces: -1

• If crossings > 0 then point is in shadow

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Shadow Volumes

• Advantages:– No aliasing. Crisp

shadow edges– Can be done on

commodity hardware– Light need not be

restricted to a frustum

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Shadow Volumes

• Advantages:– No aliasing. Crisp

shadow edges– Can be done on

commodity hardware– Light need not be

restricted to a frustum

• Disadvantages:– Needs CPU– FILL!!! 4.8 billion pixels per

second / (1024 * 1024 ) 4600 screen fills per second

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Possible Solutions

• Calculate intersection of shadow frusta with object bounding boxes

• Utilize CPU to calculate shadow polygons– Use GPUs to obtain visible set from eye and light– Intersect each eye polygon with overlapping light

frusta– Use stencil to fuse shadow polygons