Introduction to Computer Graphics

Dongguk University

Jeong-Mo Hong

CSE4030

Timetable

00:00~00:10 Introduction (English)

00:10~00:50 Topic 1 (English)

00:50~00:60 Q&A (English, Korean)

01:00~01:40 Topic 2 (English)

01:40~01:50 Quiz (English, Korean)

01:50~01:60 Q&A (English, Korean)

Week 2 • Let’s get drawing!

– How does your computer draw?

– A review on 2D graphics

Michelangelo and You

[Koller et al. 2004] [Michelangelo 1504]

Basic Graphics System

Input devices

Output device

Image formed in FB

Raster Graphics

• Image produced as an array (the raster) of picture elements (pixels) in the frame buffer

http://www.youtube.com/watch?v=Jwd5ya56wBI

Depth of Frame Buffer • Depth or precision of the frame buffer

– Determines how many colors can be represented on a give system

– 1-bit-deep frame buffer 2 colors

– 8-bit-deep frame buffer 2^8(256) colors

CPU vs GPU

http://www.youtube.com/watch?v=fKK933KK6Gg (short version) http://www.youtube.com/watch?v=ZrJeYFxpUyQ&annotation_id=annotation_764898&feature=iv (full version)

• NVIDIA – Adam & Jamie draw a MONA LISA in 80 milliseconds!

– Parallel processing on GPU's

Object Seen by Different Viewers

FIGURE 1.6 Image seen by three different viewers. (a) A’s view. (b) B’s view. (c) C’s view.

Image Formation

3D 2D

See the Difference?

Elements of Image Formation

• Objects

• Viewer

• Light source(s)

• Attributes that govern how light interacts with the materials in the scene

• Note the independence of the objects, the viewer, and the light source(s)

Ray Interactions

FIGURE 1.11 Ray interactions. Ray A enters camera directly. Ray B goes off to infinity. Ray C is reflected by a mirror. Ray D goes trough a transparent sphere.

Ray Tracing and Geometric Optics

One way to form an image is to

follow rays of light from a

point source finding which

rays enter the lens of the

camera. However, each

ray of light may have

multiple interactions with objects

before being absorbed or going to infinity.

Three-Color Theory

• Human visual system has two types of sensors

– Rods: monochromatic, night vision

– Cones

• Color sensitive

• Three types of cones

• Only three values (the tristimulus

values) are sent to the brain

• Need only match these three values

– Need only three primary colors

Object

• Where did this image come from?

Wireframe Graphics

wireframe representation of sun object

Raster Graphics

• Allows us to go from lines and wire frame images to filled polygons

Recently

• Realism comes to computer graphics

smooth shading environment mapping

bump mapping

Break and Q&A

CSE4030

The Programmer’s Interface • Programmer sees the graphics system through

a software interface: the Application Programmer Interface (API)

• OpenGL

• Open Graphics Library – API for 2D and 3D graphics programming

– GLUT – The OpenGL Utility Toolkit

First Example

glBegin(GL_POLYGON)

glVertex3f(0.0, 0.0, 0.0);

glVertex3f(0.0, 1.0, 0.0);

glVertex3f(1.0, 0.0, 0.0);

glEnd( );

type of object

location of vertex

end of object definition

Simplified Pipeline

Geometric Pipeline

• Pipeline architecture

• All steps can be implemented in hardware on the graphics card

application program

display

Vertex Processing • Much of the work in the pipeline is in converting

object representations from one coordinate system to another – Object coordinates

– Camera (eye) coordinates

– Screen coordinates

• Every change of coordinates is equivalent to a matrix transformation

• Vertex processor also computes vertex colors

Projection

• Projection is the process that combines the 3D viewer with the 3D objects to produce the 2D image

– Perspective projections: all projectors meet at the center of projection

– Parallel projection: projectors are parallel, center of projection is replaced by a direction of projection

Clipping

• Just as a real camera cannot “see” the whole world, the virtual camera can only see part of the world or object space – Objects that are not within this volume are said to be

clipped out of the scene

Primitive Assembly

• Vertices must be collected into geometric objects before clipping and rasterization can take place

– Line segments

– Polygons

– Curves and surfaces

Rasterization

• The primitives that emerge from the clipper are still in terms of their vertices

• They must be further processed to generate pixels in the frame buffer

• The output of rasterizer is a set of fragments for each primitive

• Fragments are “potential pixels” – Have a location in frame buffer

– Color and depth attributes

Fragment Processing

• Fragments are processed to determine the color of the corresponding pixel in the frame buffer

• Colors can be determined by texture mapping or interpolation of vertex colors

• Fragments may be blocked by other fragments closer to the camera – Hidden-surface removal

Lab 2

• How to Start Graphics Programming

– GLUT setup

– Visual Studio environment setting

– GLUT API

• Preparing for a canvas (window)

• Input devices (keyboard, mouse)

Reading Assignment

• Appendix B Spaces

• Appendix C Matrices

Quiz

CSE4030