Intro%20to%20OpenGL%20(Version%202)

1
Intro to OpenGL (Version 2)

• Geb Thomas

2
Setting Up GLUT

• You will need GLUT for opening windows
• We can use the version made by Nate Robins
• http//www.xmission.com/nate/glut.html
• Download the .zip file, unzip it and store it in
  a convenient directory on your drive
• I stored everything in h/documents/glut

3
Setting up the Compiler

• You need to tell the compiler where the header
  file is. One way is instead of using include
  ltglut.hgt, which assumes that the glut header file
  is in a standard location, you can use include
  h/documents/glut/glut.h. Then the compiler
  will look at this location.
• An easy way to handle the .dll file is to copy it
  to the location of your executable file, perhaps
• H\testProgram\debug

4
Setting up a Window with GLUT

• Learn about glut here http//www.opengl.org/deve
  lopers/documentation/glut/spec3/spec3.html
• glutInit(argc, argv) / initialize glut /
• glutInitWindowSize(int width, int height)
• / set the window size. 300x300 by default /
• glutInitWindowPosition(x, y)
• / set the window position, default 1, -1, which
  means let the operating system decide /

5
glutInitDisplayMode

• Use glutInitDisplayMode( GLUT_RGBA GLUT_SINGLE
  GLUT_DEPTH )
• Provides RGB color rather than indexed color
• A single frame buffer, rather than double
  buffering
• A depth buffer

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Opening a Window

• int glutCreateWindow(char name)
• Returns an integer identifier for the window
• No drawing is effective until glutMainLoop
• Several windows or subwindows may be opened.
• Windows may be resized or repositioned
• Window and display modes are system states that
  may be set and queried

7
The Main Loop

• Glut allows you to define callbacks
• void glutDisplayFunc(void (func)(void))
• void glutReshapeFunc(void (func)(int width, int
  height))
• void glutKeyboardFunc(void (func)(unsigned char
  key, int x, int y))
• void glutMouseFunc(void (func)(int button, int
  state, int x, int y))
• void glutMainLoop(void)

8
Working with OpenGL

• Get information from here (as well as other
  sources)
• http//ask.ii.uib.no/ebt-bin/nph-dweb/dynaweb/SGI_
  Developer/OpenGL_PG/

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Clearing the Window

• To clear the color to black (in RGBA mode)
• glClearColor(0.0, 0.0, 0.0, 0.0)
• glClear(GL_COLOR_BUFFER_BIT)
• To also clear the depth buffer you might use
• glClearColor(0.0, 0.0, 0.0, 0.0)
• glClearDepth(1.0)
• glClear(GL_COLOR_BUFFER_BIT GL_DEPTH_BUFFER_BIT)
  

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Drawing Colors

• The current drawing color is a state. Change the
  state with glColor3f commands such as
• glColor3f(0.0, 0.0, 0.0) // black
• glColor3f(1.0, 0.0, 0.0) //red
• glColor3f(0.0, 1.0, 0.0) //green
• glColor3f(1.0, 1.0, 0.0) //yellow
• glColor3f(0.0, 0.0, 1.0) //blue
• glColor3f(1.0, 0.0, 1.0) //magenta
• glColor3f(0.0, 1.0, 1.0) //cyan
• glColor3f(1.0, 1.0, 1.0) //white

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Flushing the Buffers

• void glFlush(void)
• Sends a command to flush out the pipeline and
  finish the drawing
• void glFinish(void)
• Waits until drawing is completed, then returns

12
Setting up a Coordinate Frame

• void reshape (int w, int h)
• glViewport (0, 0, (GLsizei) w, (GLsizei) h)
• glMatrixMode (GL_PROJECTION)
• glLoadIdentity ()
• gluOrtho2D (0.0, (GLdouble) w, 0.0,
  (GLdouble) h)