Graphics Systems I-Chen Lin’s CG slides, Doug James’s CG slides Angel, Interactive Computer Graphics, Chap 1 Introduction to Graphics Pipeline

ILE5014 Computer Graphics 08F 2 Computer Graphics Computer graphics deals with all aspects of creating images with a computer. – Hardware – Software – Applications

ILE5014 Computer Graphics 08F 3 Example Where did this image come from? What hardware/software did we need to produce it?

ILE5014 Computer Graphics 08F 4 Preliminary Answer Application: The object is an artist’s rendition of the sun for an animation to be shown in a domed environment (planetarium) Software: Maya for modeling and rendering but Maya is built on top of OpenGL Hardware: PC with graphics card for modeling and rendering

ILE5014 Computer Graphics 08F 5 Computer-generated Images Objects Viewer Light Attributes that govern how light interacts with the materials in the scene

ILE5014 Computer Graphics 08F 6 Basic Graphics System Input Device Output Device Image formed in FB

ILE5014 Computer Graphics 08F 7 Graphics System Overview Graphics API – Interface between an application program and graphics hardware – Example: OpenGL, Direct3D

ILE5014 Computer Graphics 08F 8 Graphics API Two paradigms Integrated graphics and UI toolkits – Java – portable Independent graphics and UI toolkits – OpenGL, Direct3D – may not be portable

ILE5014 Computer Graphics 08F 9 How does it work? From the programmer’s point of view: – Specify geometric objects – Describe object properties – Define how they should be viewed – Move camera or objects around for animation

ILE5014 Computer Graphics 08F 10 How does it work? From the implementer's perspective: OpenGL pipeline Rotate Translate Scale Is it visible? 3D to 2D Convert to pixels Primitives + material properties Let’s walk through the pipeline… Display

ILE5014 Computer Graphics 08F 11 3D Object Representation Curves and surfaces are inefficient to render directly

ILE5014 Computer Graphics 08F 12 3D Object Representation (cont.) We use primitives such as polygons instead

ILE5014 Computer Graphics 08F 13 Represented by Triangle Primitives A triangle is usually the most basic primitive

ILE5014 Computer Graphics 08F 14 Primitives: points, lines, polygons

ILE5014 Computer Graphics 08F 15 Primitives: Material Properties RGB Color Texture pattern

ILE5014 Computer Graphics 08F 16 Primitives: Material Properties Ambient: same at every point on the surface Diffuse: scattered light independent of angle (rough) Specular: dependent on angle (shiny)

ILE5014 Computer Graphics 08F 17 Light Sources Point light sources are common

ILE5014 Computer Graphics 08F 18 Transform Rotate Translate Scale

ILE5014 Computer Graphics 08F 19 Camera Views Different views of an object in the world

ILE5014 Computer Graphics 08F 20 Synthetic Camera Model Creates images as using photographing center of projection image plane projector p projection of p

ILE5014 Computer Graphics 08F 21 Perspective Projection Objects farther away are smaller in size Lines from each point on the image are drawn through the center of the camera lens (the center of projection (COP)).

ILE5014 Computer Graphics 08F 22 Camera Transformations Camera positioning just results in more transformations on the objects: – Transformations that position the object relative to the camera – Handled in the transformation process in the pipeline up COP eye

ILE5014 Computer Graphics 08F 23 Clipping Not everything is visible on the screen

ILE5014 Computer Graphics 08F 24 Hidden Surface Elimination If we draw objects directly, our screen will be a “mess”. Remove hidden surfaces.

ILE5014 Computer Graphics 08F 25 Rasterizer Transforms pixel values in world coordinates to pixel values in screen coordinates

ILE5014 Computer Graphics 08F 26 A realistic 3D view Delicate 3D models Perspective Hidden surface removal Shading (lighting & reflection) Shadow Detailed textures and normals “Geri’s Game”, Pixar B. Martin, U. Utah

ILE5014 Computer Graphics 08F 27 How to synthesize a view? How to represent a object? How to make the scene “move”? How to display a 3D scene on screen?

ILE5014 Computer Graphics 08F 28 Try the following tutorial at home