02/04/03Page 1

Rendering

• Visibility

• Lighting

• Texturing

02/04/03Page 2

• 1. Application/Scene– Description of the contents of the 3D world

– Object Visibility Check including possible Occlusion Culling

• 2. Geometry – Transforms (rotation, translation, scaling)

– Transform from Model Space to View Space

– View Projection

– Trivial Accept/Reject Culling

– Transform to Clip Space

– Clipping

– Transform to Screen Space

• 3. Triangle Setup – Back-face Culling (or can be done in view space before lighting)

– Scan-Line Conversion

• 4. Rendering / Rasterization – Shading

– Texturing

– Fog

– Alpha Translucency Tests

– Depth Buffering

– Z-buffer

Pipeline

02/04/03Page 3

CPU vs. GPU

From http://www.gamedev.net/reference/programming/features/d3d7im2/page2.asp

Move Object and Camera

(AI, Realistic Physics)CPU CPU CPU CPU CPU CPU

Scene Level Calculations,High order surface tessellation

CPU CPU CPU CPU CPU GPU

Transforms CPU CPU CPU GPU GPU GPU

Lighting CPU CPU CPU GPU GPU GPU

Triangle Setup and Clipping CPU CPU CPU GPU GPU GPU

RenderingGraphicsProcessor

GraphicsProcessor

GraphicsProcessor

GPU GPU GPU

1996 1997 1998 1999 2000 2002+

02/04/03Page 4

VisibilityObject Visibility Tests / Occlusion Tests

• Bounding boxes– Approximate objects for quick tests

Area occluded by bounding box of A

A

Note that B is not fully occluded by object A

B

02/04/03Page 5

VisibilityObject Visibility Tests / Occlusion Tests

• QuadTrees– Partition space

02/04/03Page 6

VisibilityObject Visibility Tests / Occlusion Tests

• QuadTrees/OctTrees– Partition 3D space

02/04/03Page 7

VisibilityObject Visibility Tests / Occlusion Tests

• QuadTrees/OctTrees/BSP– Partition space to create a binary tree

02/04/03Page 8

VisibilityObject Visibility Tests / Occlusion Tests

• Portals

02/04/03Page 9

View Space

Near Clipping Plane

Far Clipping Plane

View Frustum

View point

Polygon clipping

02/04/03Page 10

Shading models

• Simple model has 3 basic elements– Diffuse (direct reflection)

– Ambient (reflected and scattered light from the environment)

– Specular (highlights from surface)

• Notes– not physically-based and inaccurate

– nevertheless, a decent approximation

– fast to compute

02/04/03Page 11

Shading models• Diffuse (Lambertian) Reflection

– Dull, matte surfaces– Viewer position independent– Dependent on position and intensity of source

Reflection is product oflight ray L and surface normal N

Light (Ip)N

L

Light (Ip)

NL

Light (Ip)

N

L

But this doesn’t look very good … lighting is too harsh(See this example)

I = Ip kd (N • L) (kd is coeff. of diffusion)

02/04/03Page 12

Ambient Light• So we add ambient light

– Constant term– Crude approximation of light scattering in

scene– Independent of object, light, or viewer position

From http://www.siggraph.org/education/materials/HyperGraph/shutbug.htm

I = Ia ka + Ip kd (N • L)

02/04/03Page 13

Specular Reflection

• To get more accurate and model highlights off the surface, we add specular reflection.

• This adds reflection proportional to cosnα

I = Ia ka Ca + Ip [kd Cd(N • L) + ks Cs(R • V)](C is object color)

Light (Ip)N

LR

V

Reflected ray

To viewer

02/04/03Page 14

Shininess: 0 Shininess Strength: 0

Shininess: 0 Shininess Strength: 33

Shininess: 33 Shininess Strength: 66

Shininess: 66 Shininess Strength: 100

Shininess: 100 Shininess Strength: 100

From http://cts.rice.edu/~shisha/projects/ravl/3ds/materials/shininess.html

Specular coefficients

02/04/03Page 15

All together

Note: mach banding in Gouraud

Flat Gouraud Phong

02/04/03Page 16

• Ambient

• Point sources

• Directional lights (infinite source)

• Spot lights

• Area lights

• Local lights

Lights

X

02/04/03Page 17

Texture• uv coordinates

0,1 1,1

0,0 1,0

0,1 1,1

1,00,0

02/04/03Page 18

From Gamedev.net

Mip Mapping

R

G B

R

G B

R

G B

02/04/03Page 19

Multi passes• Provides application of “textures” to texttures• Quake III uses 10 passes:

– (passes 1 - 4: accumulate bump map) – pass 5: diffuse lighting – pass 6: base texture (with specular component) – (pass 7: specular lighting) – (pass 8: emissive lighting) – (pass 9: volumetric/atmospheric effects) – (pass 10: screen flashes)

(From: Brian Hook, course 29 notes at SIGGRAPH '98)

02/04/03Page 20

Bump Mapping

02/04/03Page 21

Reflection and refraction

From http://www.gamasutra.com/features/20001110/oliveira_01.htm

Snell’s Law : ir1*sin (1) = ir2*sin (2)

02/04/03Page 22

Environment Mapping

Environment mapped onto cube,then projected onto object

02/04/03Page 23

Light mapping

X =

From http://www.gamedev.net/reference/programming/features/d3d7im3/page4.asp

•Pre-computed “texture map”•Simulates light sources

02/04/03Page 24

Alpha blendingFinalColor = SourcePixelColor * SourceBlendFactor +

DestPixelColor * DestBlendFactor

From http://www.gamedev.net/reference/programming/features/d3d7im3/page5.asp

02/04/03Page 25

Z buffer

Each pixel in the buffer contains the distance from the viewpoint of the object rendered at that pixel

If the next object to be drawn at that pixel is further then the value at the pixel, then don’t write the pixel.

Note: ATI Radeon’s Hierarchal Z-buffering

02/04/03Page 26

Reading

• 3D pipeline tutorialhttp://www.extremetech.com/article/0,3396,s=1017&a=2674,00.asp