Introduction to Computer Graphics

1. Introduction to Computer Graphics CS 4363/6353

2. What You’ll see • Interactive 3D computer graphics • Real-time • 2D, but mostly 3D • OpenGL • C/C++ (if you don’t know them) • The math behind the scenes • Shaders • Simple and not-so-simple 3D file formats (OBJ and FBX)

3. What you Won’t See • Applications (though they are useful) • Photoshop/Gimp/Paint.NET • Maya • Web graphics • Art • Character animations • Very complex • Usually require 3rd party software

4. WhY? • Senior Graphics Engineer at Autodesk – 1/6/2012

5. Why? • C/C++ Game Programmer at Addmired – 1/5/2012

6. Why? • Graphics Engineer at LucasArts – 1/4/2012

7. Early Graphics • Das Blinkenlights • Dot matrix printers • Shortly after printers came the CRT… http://james.seng.sg/files/public/starwar-ascii-art.jpg

8. Early Graphics • The CRT was able to draw more than ASCII characters. It could draw dots! http://www.gamasutra.com/view/feature/3900/the_history_of_pong_avoid_missing_.php

9. Early Graphics • If you can draw a dot, you can draw a line! • Bresenham’s Line Drawing algorithm http://kobi.nat.uni-magdeburg.de/patrick/uploads/BEng/bresenham_line.png http://i18.photobucket.com/albums/b106/mspeir/Grid.jpg

10. Things to Note… • Everything at this time • was 2D • Looked really bad, but was playable! • was in real time • How did the “animation” work?

11. Into the 3rd Dimension • Add depth dimension • How do you perceive depth everyday? • You have two eyes • The image for your left eye is different than the right • Brain extracts the differences to understand depth • 3DTVs – how do they work? http://static3.businessinsider.com/image/4b45f3b20000000000533ed7/3d-tv.jpg

12. But Wait! • Monitors are one “flat image on a flat surface” • How do we perceive depth now? • Farther objects are smaller (foreshortening) • Subtle lighting changes • We’ll use mathematics to do this for us http://www.oceansbridge.com/paintings/artists/c/canaletto/oil-big/perspective_1765_XX_venice.jpg

13. Common TErminology • Rendering: the entire process of drawing an image to the screen • Vertex: a single 3D point (x, y, z) • Edge: a line between two vertices • Face: Most often 3 vertices and their edges • Transformations: moving one or more vertices • Translate: pushing vertices along the x, y or z axis • Rotate: revolving vertices around some 3D point • Scale: increasing or decreasing the distance of vertices from their center • Model matrix – a mathematical structure for holding transformations (later) • View matrix – another used for holding the viewpoint (camera) • Projection matrix – another, used to get images on the screen (later) • Rasterization– putting the actual pixels on the screen (final phase of rendering)

14. Transformations • Translate • Rotate • Scale

15. Terminology(IMAGE From the OpenGL SuperBible) • Wireframe – rendering only the edges of the model (old games)

16. Terminology(IMAGE From the OpenGL SuperBible) • Hidden Surface Removal (HSR) – occluded objects can’t be seen • Backface culling - drawing only the triangles that are facing the camera

17. Terminology(IMAGE From the OpenGL SuperBible) • Solid shading (this isn’t a definition) – note that everything’s hard-coded red!

18. Terminology(IMAGE From the OpenGL SuperBible) • Flat Shading – simulate lighting

19. Terminology(IMAGE From the OpenGL SuperBible) • Texture mapping – using an image during the rasterization process

20. Terminology(IMAGE From the OpenGL SuperBible) • Blending – mixing colors by rendering more than one thing in one spot • The floor is rendered semi-transparent (yes, there are two cubes)

21. What about this?(non-Real-time)

22. Coordinate Systems • We have several spaces: • Local/Object – the coordinate system the mesh was modeled in • World – the coordinate system of the virtual environment • View/Camera – the coordinate system relative to the camera • Clip – windowing system • We use mathematics to transform vertices from one space to another

23. Coordinate Systems(for Windowing Systems) • Because your screen is flat, we must work with 2D Cartesian Coordinates • x = horizontal, y = vertical • (0, 0) is origin +y -x +x -y

24. Coordinate CLipping • When creating a window, we must define where we are in the Cartesian system • The window header doesn’t count in this equation • Middle of screen is (0, 0) +75 +100 -100 -75

25. Another Example • Middle of screen is (75, 100) +150 +200 0 0

26. Setting A Window’s Viewport • Window size usually doesn’t match clipping size • The viewport maps the clipping area to part (or all) of the window • Most often, the viewport fills the entire window • Sometimes, you want a “Picture in Picture” (PIP) rendering

27. Example – Entire Window (150, 200) 1900x1200 Window 0 0

28. PIP Example (150, 200) 1900x1200 Window 0 0

29. 3D Coordinate Systems • We live (and think) in 3 dimensions • x = horizontal, y = vertical, z = depth (can be RHS or LHS) • (0, 0, 0) is origin +y -z -x +x +z -y http://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/s2010/ky237_zy49/ky237_zy49/index.html

30. Basic Problem • We need to convert our 3D models and display them on a 2D screen • To do this, we use projections by defining a viewing volume • These “flatten” the 3D world • There are two kinds: • Orthographic (aka “parallel”) • All objects that have the same dimension are the same size, regardless of distance • Viewing volume is rectangular • Perspective • Objects shrink with distance • Viewing volume is shaped like a pyramid

31. Example(Upper-right is a Perspective View)

32. Orthographic View Volume(you can see the parallel now…) Far clipping plane Near clipping plane

33. Perspective View Volume Far clipping plane Near clipping plane