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3D Computer Graphics in a Nutshell Guillaume Caumon, January 2002 Introduction Computer graphics is concerned with all the aspects of “drawing” on computers Performance is critical 3D Computer Graphics deals with the generation images from 3D objects. The Rendering Pipeline

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3D Computer Graphics in a Nutshell

Guillaume Caumon, January 2002


Introduction

  • Computer graphics is concerned with all the aspects of “drawing” on computers

  • Performance is critical

  • 3D Computer Graphics deals with the generation images from 3D objects.


The Rendering Pipeline

Pipeline = Linear succession of operations

Rendering speed = speed of the slowest step (bottleneck)

Application

Geometry

Rasterization


meshing

decimation

collision detection

animation

Application

Software-based processing / modifications

Rendering

primitives

3D Model


Geometry

Transforms

Lightning

Projection

Clipping


Geometry : Transforms

Model Transform

Model Coordinates

World Coordinates

Scaling, etc.

View Transform

Viewing Coordinates


Geometry: lighting and shading

Simulate interaction of light with matter:

- Emission

- Absorption

- Reflection


L

α

N

β

IR(l)

Ambient light coefficient

Ex: (.1, .1, .1)

Material color

Ex: (1, 0, 0)

Specular Coeficient

Ex: (1, 1, 1)

ν : r, g or b

Shininess (s > 1)

Geometry: A Lightning Equation


Geometry: Shading

Flat shading: each triangle has

the same color

Gouraud shading: colors are

interpolated between vertices

Phong shading: normal are

interpolated and colors computed

for each pixel


Geometry: Projection

normalization

Viewing Coordinates

Virtual Device Coordinates

Perspective/

parallel


Geometry: Clipping


Geometry: Device Coordinates

My Window

Unit Cube


Rasterization

Screen = matrix

Per-pixel operations: ray-tracing

Scan conversion of lines:

naive version

Bresenham algorithm

Scan conversion of polygons

Aliasing / antialiasing

Texturing


Graphics Hardware

Quickly evolving

Main principle: use of buffers

Color buffer :

1 byte per pixel (256) + lookup tables

2 bytes per pixel (65 536) “high color”

3+1 bytes per pixel bpp (16 millions) “true color” + alpha channel

Depth buffer :

16 to 32 bit per pixel


Graphics Hardware (II)

  • Double buffering :

    • show the front buffer while rasterizing the back buffer

    • swap buffers in synchronization with the screen refresh

  • to get the new frame

  • Stencil buffer :

    allows high-level operations (antialiasing, filtering, etc.)

    See OpenGL programmer’s reference for more details


    Conclusion

    3D Graphics require intensive computations

    Yet, 3D Graphics are time-critical

    Bottlenecks

    Display lists

    Only low-level graphics have been described.

    }

    Scene Graphs

    Selection and tools

    See OpenInventor, VTK, etc.


    References and further reading

    • Foley, van Dam, Feiner, Hughes, Computer Graphics Principle and practice,2nd edition. Addisson Wesley, 1997

    • Moller, Haines, Real-Time Rendering. AK Peters, 1999 (http://www.realtimerendering.com)

    • The Graphic Gems series, Academic Press.

    • Neider, Davis, Woo, OpenGL Programming Guide. Addisson Wesley, 1993

    • Wernecke, The Inventor Mentor, release 2, Addisson Wesley,1994

    • Schroeder, Martin, Lorensen, The Visualization Toolkit, 2nd edition. Prenctice Hall, 1998

    • Proceedings of Siggraph, Visualization, Eurographics, etc.


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