Computer Graphics

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Computer Graphics

• OpenGL

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What is OpenGL?

• A low-level graphics library specification
• designed for use with the C and C
• provides
• a set of commands that allow the specification
  of geometric objects in two or three dimensions
• graphics primitives
• commands that control how these objects are
  rendered into the frame buffer

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Libraries
Gl.h

• gl.h - GL foundation
• glu.h - GL utilities
• glaux.h - GL auxiliary
• glut.h - GL utility toolkit

Glaux.h
Glu.h
Glut.h
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What does GLUT do for us?

• Allows us to initialize a GL program using fewer
  function calls than with just GL
• Allows us to still access the lower level GL, GLU
  and GLAUX calls

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GLUT main( )
Command-line arguments

• void main(int argc, char argv)
• glutInit(argc, argv)
• glutInitDisplayMode(GLUT_DOUBLE GLUT_RGB
  GLUT_DEPTH)
• glutInitWindowSize(100,100)
• glutInitWindowPosition(0,0)
• glutCreateWindow("GL Example")
• init()
• glutDisplayFunc(display)
• glutReshapeFunc(reshape)
• glutIdleFunc(animate)
• glutMouseFunc(handleEvent)
• glutMainLoop()

Display mode tokens
Window size and position
Creates window
Specifies display, reshape, idle and mouse
functions
Starts execution
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glutInit ( )

• Initialize the GLUT library and negotiate a
  session with the window system
• May cause the termination of the GLUT program
  with an error message to the user if GLUT cannot
  be properly initialized
• Processes command line options, but the specific
  options parse are window system dependent.

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glutInitDisplayMode( )

• GLUT_RGB
• Bit mask to select an RGBA mode window. This is
  the default if neither GLUT_RGBA nor GLUT_INDEX
  are specified.
• GLUT_SINGLE /GLUT_DOUBLE
• Bit mask to select a single buffered or double
  buffered window.
• GLUT_DEPTH
• Bit mask to select a window with a depth buffer.
• GLUT_STEREO
• Bit mask to select a stereo window.

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glutInitWindowSize(int width,int
height)glutInitWindowPosition(int x,int
y)glutCreateWindow(Title)

• Windows created by glutCreateWindow will be
  requested to be created with the current initial
  window position (x,y) and size (width,height)

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init( )

• void init (void)
• // Additional user specified GL calls, such as
  ...
• glClearColor(1,1,1,0.0)
• glShadeModel(GL_SMOOTH)

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glutDisplayFunc( )

• Sets the display callback for the current window
• When GLUT determines that the normal plane for
  the window needs to be redisplayed, the display
  callback for the window is called
• Before the callback, the current window is set to
  the window needing to be redisplayed and (if no
  overlay display callback is registered) the layer
  in use is set to the normal plane.

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glutReshapeFunc( )

• Sets the reshape callback for the current window
• The reshape callback is triggered when a window
  is reshaped
• A reshape callback is also triggered immediately
  before a window's first display callback after a
  window is created or whenever an overlay for the
  window is established
• The width and height parameters of the callback
  specify the new window size in pixels
• Before the callback, the current window is set to
  the window that has been reshaped

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glutIdleFunc( )

• Sets the global idle callback so a GLUT program
  can perform background processing tasks or
  continuous animation when window system events
  are not being received
• If enabled, the idle callback is continuously
  called when events are not being received

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glutMouseFunc( )

• Sets the mouse callback for the current window
• When a user presses and releases mouse buttons in
  the window, each press and each release generates
  a mouse callback
• The button parameter is one of GLUT_LEFT_BUTTON,
  GLUT_MIDDLE_BUTTON, or GLUT_RIGHT_BUTTON
• The state parameter is either GLUT_UP or
  GLUT_DOWN
• The x and y callback parameters indicate the
  window relative coordinates when the mouse button
  state changed

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glutMainLoop( )

• Enters the GLUT event processing loop
• This routine should be called at most once in a
  GLUT program
• Once called, this routine will never return
• It will call as necessary any callbacks that have
  been registered