1 Dynamic Shadows and Lighting for Walkthrus of Large Models Brandon Lloyd COMP 258 December 2002

2 Why Are Shadows Important?

3

4 Shadow Maps EyeLight

5 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.

6 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

7 Perspective Shadow Maps Standard Shadow MapPerspective Shadow Map

8 Perspective Shadow Maps Standard Shadow MapPerspective Shadow Map

9 Perspective Shadow Maps Standard Shadow MapsPerspective Shadow Maps

10 Benefits of Using Cg

11 Benefits of Using Cg

12 Shadow Volumes 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

13 Shadow Volumes Advantages: –No aliasing. Crisp shadow edges –Can be done on commodity hardware –Light need not be restricted to a frustum

14 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

15 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