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OpenGL Help Session

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  1. OpenGL Help Session • CS248 Fall 2006 • Zhengyun Zhang

  2. References • OpenGL Programming Guide (Red Book) • start here • OpenGL Reference Guide (Blue Book) • use this to look up individual functions • OpenGL Shading Language (Orange Book) • gets you started with GLSL

  3. OpenGL is a state machine • States like projection matrix, current vertex color, etc. • We can change the states by using GL function calls like glPushMatrix. • The state is used when we are drawing primitives.

  4. OpenGL needs to be connected to the windowing system • OpenGL by itself does not talk to the windowing system/manager by itself. • Need a toolkit to tell the windowing system that we need an OpenGL window. • Examples: • GLUT (used in Project 2) • SDL (recommended for Project 3) • wxWidgets, Qt (full fledged widget toolkits, probably overkill for a game)

  5. OpenGL function suffixes • OpenGL functions that take different types of arguments while providing the same functionality will often have a suffix to denote which type of function they are: • glVertex2i - input is 2 integers • glVertex3fv - input is 3 floats in an array • glVertex3f - input is 3 floats

  6. OpenGL function suffixes • Extensions to the OpenGL base system often have their own suffixes. For example: • glCreateProgramObjectARB(to create a shader program using an ARB extension) • Use GLEW (OpenGL Extension Wrangler) for easy access to extensions.

  7. Other OpenGL Hints • OpenGL uses a right-handed coordinate system. • Light positions are not sent through the Model-View matrix. • Projection matrix should only be used for camera position, etc. It has a shorter stack than the Model-View matrix. • New matrix is multiplied on the right. Latest matrix to be multiplied on is the first operation to be performed on the vertex locations.

  8. Basic OpenGL Game Flowchart • Load up an OpenGL window using a toolkit to talk to the windowing system • Set up projection matrices, shading properties, etc. Load textures, etc. • Event loop: • Check for any events or user input and process them • Redraw the OpenGL scene as necessary • Wait a small amount of time.

  9. Sample OpenGL Program • Based on the example SDL application Andrew wrote that’s linked off the project 3 handout:http://graphics.stanford.edu/courses/cs248-06/SDLDemo.zip • I’m going to demonstrate a Python version, but the overall structure of the program should be the same.

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