CPCS 391
Computer Graphics 1
Instructor: Dr. Sahar Shabanah
Graphics Applications
Course description
• First course in computer graphics covering fundamental
concepts and techniques related to 2-D and 3-D graphics.
– Rasterization
– Geometry
– Shading
– Hidden surface
elimination
– Texture mapping
– Modeling
– Animation
– Ray tracing
– Global illumination
– Animation
from M. Woo et al., 1997
Course Outline
– Rasterization
– Geometry
Advanced
Topics
How to
to apply
set
individual
image
pixels
corresponding
to
How
to
specify
model
efficiently
light
therasterize
3-D
interaction
onlywith
the
ofscene
the
visible
3-Dcamera
“layers”
ofpositions
detail
to
objects
projected
geometric
objects
asvarious
points,
lines,
and
surfaces
parts
the
of features,
scene
with
varying
objects
material
and such
theirproperties
parts,
in
to
show
simulate
bumps
and
polygons,
and
more
complicated
shapes.
Antihow
order
totoproject
calculate
these
theprecomputed
to
proper
2-D image
colorslocations,
perceived
reflections,
or other
shading
aliasing
reduces
artifacts
(“jaggies”)
caused
bythese
finite
andthe
by
how
eyetoatrepresent
differenttrans-formations
image locations of
image resolution
effects.
positions
– Shading
– Hidden surface
elimination
– Texture mapping
– Modeling
– Ray tracing
from M. Woo et al., 1997
– Global illumination
Learning objectives of this course
• Basic understanding of graphics
hardware/software technology and
algorithms
• Learn how to use OpenGL to write
2D/3D drawing programs
Lectures
• ST, 11:00 pm-12:30 pm
• Lecture slides will be posted on the course page
before each lecture.
• Read thru the lecture notes and the assigned
readings before class.
• Be prepared to ask questions.
• Class website:
http://groups.yahoo.com/group/CPCS391_F10/
Textbooks
Any one of these:
1. Fundamentals of Computer Graphics, Peter
Shirley, 3rd Revised edition edition (July 21,
2009), ISBN-10: 1568814690, ISBN-13: 9781568814698
2. Computer Graphics, C Version (2nd Edition),
Donald Hearn, M. Pauline Baker, ISBN-10:
0135309247, ISBN-13: 978-0135309247
(course website)
3. Computer Graphics in C#: Principles and
Practice, 3Rev Ed edition, 2008, Authors:
James D. Foley, Andries van Dam, Steven K.
Feiner, John F. Hughes, ISBN-10: 0321399528,
ISBN-13: 978-0321399526 (old copy in CS
dept.)
Grading
•
•
•
•
•
20% Lab & Assignments
15% Exam 1: Tuesday 27/4-20/3
15% Exam2: sunday 8/6-29/4
30% Final Project
20% Final exam
Computer Graphics
Computer-generated images and
models or sequences of such
models and images (i.e.,
animations, movies)
The scientific study of techniques
and methods for generating such
images: creation, storage and
manipulation.
Computer Graphics Systems
Interactive
User controls contents, structure, and
appearance of objects and their displayed
images via rapid visual feedback
Non-interactive
batch mode
Basic components
used for:
• Input: mouse, tablet and stylus, multi_touch
• processing (and storage)
• display/output :screen, printer, video recorder
• final production-quality video
• film (special effects – FX)
First interactive graphics system, Sketchpad,
3-D Computer Graphics Applications
Manufacturing design (CAD)
Movies, TV, commercials
• Animations
• Special effects mixed with live footage
Visual arts
Video games
Scientific visualization
Simulation of natural phenomena
Enabling Modern Computer Graphics
Hardware
revolution
Every 12-18 months,
computer power
improves by factor of 2
in price / performance
as size shrinks
Newest processors are 64bit, 2, 4, 6, 8, or 12 core
• Intel Core i7 – consumer,
4 cores hyper-threaded
to provide 8 threads
Graphic subsystems
GPU:
- chip designed for doing graphics
operations fast
- Offloads graphics processing from
CPU
•nVidia GeForce™, ATI Radeon™
•Advanced Per-pixel lighting
•Millions of triangles per second
•special purpose computation,
• ganged together to make
supercomputers
nVidia GeForceTM chip
Significant advances in GPUs every 6
months vs. several years for CPUs
Enabling Modern Computer Graphics
Input
Devices
•
•
•
•
•
Mouse,
tablet & stylus,
multi-touch,
force feedback,
game controllers (e.g.,
Wii),
• scanner,
• digital camera
• Whole body as
interaction device:
• http://www.xbox.co
m/kinect
Enabling Modern Computer Graphics
Cell Phones/PDAs (smartphones), Laptop/Desktops,
Jeff Han’s Perceptive Pixel, Microsoft Surface
Micro
soft
Surfa
ce
3D immersive virtual reality systems such as Brown’s Cave™
Enabling Modern Computer Graphics
Software Improvements
Algorithms and
data structures
Parallelization
Distributed and
Cloud computing
• Modeling of
materials
• Rendering of
natural
phenomena
• Acceleration
data structures
for ray tracing
• Most
operations are
embarrassingly
parallel:
changing value
of one pixel is
often
independent of
other pixels
• Send
operations into
‘cloud’, get
back results,
don’t care how
• Rendering even
available as
internet
service!
Graphics Display Hardware
Vector
Raster
• Calligraphic, stroke,
random-scan
• Draw driven by display
commands (Draw List):
– move (x, y),
– char(“A”) ,
– line(x, y)
Ideal
Drawing
Vector
Drawing
• (TV, bitmap, pixmap) used in
displays and laser printers
• Draw driven by array of
pixels (frame buffer): no
semantics, lowest form of
representation
• “Jaggies” (aliasing errors)
due to sampling continuous
primitives
Raste
r
Conceptual Framework for Interactive Graphics
•
•
•
•
Graphics library is intermediary between application and display hardware (Graphics
System)
Application program maps application objects to views (images) of those objects by
calling on graphics library. Application model contains non-graphical data (e.g., nongeometric object properties)
User interaction results in modification of model and/or image
Unlike with FX, images are often means to an end: synthesis, design, manufacturing,
visualization,…
Software
Application
Model/data
base
Application
program
Hardware
Graphics
Library
Graphics
System/GP
U
Graphics Libraries
•
•
•
•
•
•
Examples: OpenGL™, DirectX™, Windows
Presentation Foundation™ (WPF), RenderMan™
Primitives (characters, lines, polygons, meshes,…)
Attributes: color- line style- material properties for 3D
Lights
Transformations
Immediate mode vs. retained mode
– immediate mode: no stored representation, package
holds only attribute state, and application must
completely draw each frame
– retained mode: library compiles and displays from
scenegraph that it maintains, a complex DAG. It is a
display-centered extract of the Application Model
Graphics Application Distinctions
Sample-based graphics:
• discrete samples to describe visual information
• pixels can be created by digitizing images, using a
sample-based “painting” program, etc.
• example programs: Adobe Photoshop™, GIMP™
Geometry-based graphics:
• geometrical model, appearance attributes,
sampled for visualization (rendering)
• aspects of physical world is visually simulated
• Examples:
• 2D apps: Adobe Illustrator™, Adobe
Freehand™, Corel CorelDRAW™
• 3D apps: Autodesk’s AutoCAD2010™, Maya™,
3D Studio Max™
18
Sample-based Graphics
Images are made up of grid of discrete pixels, for 2D “picture elements”
Pixels are point locations with associated sample values, usually of light
intensities/colors, transparency, and other control information
An image is sampled using points locations along the continuous signal and
we cannot treat the pixels as little circles or squares
light intensity
CRT beam illumination pattern
1 pixel
Mathematical
pixel grid
LCD display
NB: Can’t resolve adjacent
pixels on CRT
19
Sample-based Graphics
Samples creation
• directly in paint-type program,
• as a sampling of continuous (analog) visual materials. E.g.,
photograph can be sampled (light intensity/color measured at
regular intervals) with scanners, cameras
• Sample values can also be input numerically (e.g., with numbers
from computed dataset)
image manipulation
• Image editing: changes made by user, such as cutting and pasting
sections, brush-type tools, and processing selected areas
• Image processing: algorithmic operations that are performed on
image without user intervention. Includes blurring, sharpening,
edge-detection, color balancing, rotating, and warping. Preprocessing step in computer vision
20
Sampling an Image
3D scene
•
A color value is measured at every grid point and used to color corresponding grid square
•
Note: this poor sampling and image reconstruction method creates blocky image
0 = white, 5 = gray, 10 = black
21
What’s the Advantage?
Image alteration
• image defined in terms of colors at (x, y) on grid,
• change image by altering location or color values
• E.g. reverse mapping above and make 10 = white
and 0 = black,
Image combining
• Pixel information from one image can be copied and
pasted into another, replacing or combining with
previously stored pixels
22
What’s the Disadvantage?
WYSIAYG (What You See Is All You Get):
• No additional information, no depth information
• can’t examine scene from different point of view
• at most can play with the individual pixels or groups of pixels to change colors,
enhance contrast, find edges, etc.

Image-based
rendering to fake 3D
scenes and arbitrary
camera positions.

Images constructed
by interpolation,
composition,
warping and other
operations.
Photo Tourism: Exploring photo collections in 3D
(Siggraph 2006)
23
Geometry-Based Graphics
Geometry-based graphics applications
• store mathematical descriptions, or “models,” of
geometric elements (lines, polygons, polyhedrons…) and
associated attributes (e.g., color, material properties).
• Elements are primitive geometric shapes, primitives for
short
• Images created as pixel arrays (via sampling of geometry)
for viewing, but not stored as part of model. Images of
many different views are generated from same model
• Users cannot usually work directly with individual pixels in
geometry-based programs; as user manipulates geometric
elements, program resamples and redisplays elements
• Increasingly rendering combines geometric and samplebased graphics, both as performance hack and to increase
quality of final product
24
What is Geometric Modeling?
What is a model?
•Captures salient features (data, behavior) of thing/phenomenon
being modeled
•data includes geometry, appearance attributes…
•Modeling is coping with complexity
Geometry Types
• Real: some geometry inherent
• physical (e.g., actual object such as a pump)
• non-physical (e.g., mathematical function, weather data)
• Abstract: no inherent geometry, but for visualization
• organizational (e.g., company org. chart)
• quantitative (e.g., graph of stock market)
25
Decomposition of a Geometric Model
• Divide and Conquer
• Hierarchy of geometrical components
• Reduction to primitives (e.g., spheres, cubes, etc.)
• Simple vs. not-so-simple elements (nail vs. screw)
Head
Shaft
Point
composition
decomposition
26
Hierarchical (Tree) Diagram of Nail
•
•
Object to be modeled is (visually) analyzed, and then decomposed into collections of
primitive shapes.
Tree diagram provides visual method of expressing “composed of” relationships of
model
Nail
Head
Body
(cylinder)
Shaft
Point
(cylinder)
(cone)
tree diagram
•
•
root node
leaf nodes
Such diagrams are part of 3D program interfaces (e.g., 3D Studio MAX, Maya)
As pointer data structure to be rendered, it is called a scenegraph
27
Composition of a Geometric Model
Translate
Translate and Scale
Translate and Rotate
Primitives
in their own modeling
coordinate system
Composition
in world (root)
coordinate system
• Primitives created in decomposition process must be
assembled to create final object. Done with affine
transformations, T, R, S (as in above example).
28
Modeling vs. Rendering
Modeling
•
•
•
•
•
Rendering
Create models
Apply materials to models
Place models around scene
Place lights in scene
Place the camera

Take “picture” with camera
Both can be done by modern commercial
software:
Autodesk MayaTM ,3D Studio MaxTM,
BlenderTM, etc.
Point Light
Spot
Light
Directional Light
Ambient
Light
lighting assignment by Patrick Doran, Spring 2009
29