05 Graphics Pipeline

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Universidade Federal da Paraíba
Centro de Informática
Introduction to the
Graphics Pipeline
Lecture 5
1107190 - Introdução à Computação Gráfica – Turma 01
Prof. Christian Azambuja Pagot
CI / UFPB
Universidade Federal da Paraíba
Centro de Informática
Coordinate Systems
● Almost everything in CG revolves around 
coordinate systems:
– Object description.
– Object transformation.
– Camera definition.
– Projection onto the screen.
Universidade Federal da Paraíba
Centro de Informática
What is the Graphics Pipeline?
The Graphics Pipeline comprises the sequence 
of steps needed to transform the 
mathematical/geometric description of a scene 
into a discrete image on the screen.
Basically, each step of the pipeline 
transforms geometric descriptions from 
one coordinate system (space) to another!
Universidade Federal da Paraíba
Centro de Informática
Model Description
● It is accomplished in the Object Coordinate 
System (or Object Space).
y
x
Blender (www.blender3d.org)
y
x
Object Space
(3D Model)
Universidade Federal da Paraíba
Centro de Informática
Putting Everything Together
● It is done in the World Coordinate System (or 
World Space).
y
x
y
x
Object Space
(3D Model)
World Space
y
x
Universidade Federal da Paraíba
Centro de Informática
Aiming the Camera at the Scene
● The camera defines a new coordinate system: 
the Camera Coordinate System (or Camera 
Space).
Camera Space
y
x
World Space
Universidade Federal da Paraíba
Centro de Informática
Taking the Picture: From 3D to 2D
● The camera also defines whether parallel or 
perspective projection will be used.
Parallel Projection
View plane
Object in 
Camera Space
Perspective Projection
View plane
Object in 
Camera Space
Universidade Federal da Paraíba
Centro de Informática
Remember the PutPixel() func.?
● Pixels are addressed through the Screen 
Coordinate System (or Screen Space).
View plane
Viewport on the Screen
Window
Universidade Federal da Paraíba
Centro de Informática
The Whole Graphics Pipeline
Object Space
(3D Model)
y
z
Object 
space
Camera Space
Camera 
space
Clipping Space
Clipping 
space
World Space
World 
space
Universidade Federal da Paraíba
Centro de Informática
The Whole Graphics Pipeline
Object Space
(3D Model)
World Space Camera Space Clipping Space
Screen Space
y
z
Clipping 
space
Canonical
Space
Canonical (NDC) 
space
(0,0) (w-1,0)
(w-1,h-1)(0,h-1)
y
x
Screen
space
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