OpenGL

1
OpenGL
2
Relevant Libraries
OpenGL
C/C Code
Graphics Hardware
GLU
Win32
OpenGL Application
GLUT
C/C Libraries

• OpenGL has no windowing functions of its own
• We need to use something like the GLUT libraries
  for windowing operations etc.

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Setting up to use OpenGL in MS Visual Studio

• If you have Visual Studio 6, you should already
  have the OpenGL libraries installed.
• You will need the following files for GLUT
• glut32.dll, glut.h, glut32.lib
• The GLUT source files and examples can be
  obtained at various sites on the web but the
  above (minimum required) files precompiled can be
  obtained on my page at
• http//isg.cs.tcd.ie/dingliaj/3d4ii/glut37p.zip
• You should extract the glut files and put them in
  a directory visible to your project
• You need to link the following libraries into
  your project (In Project-gtSettings Link Tab
  General under Object/Library Modules insert
  opengl32.lib glu32.lib glut32.lib)
• In your source code make sure you include glut.h
  wherever you need to use OpenGL or Glut
  functions/variables
• For more information see http//isg.cs.tcd.ie/ding
  liaj/cs5/glutsetup.html or you can email me for
  specific questions

4
Simple GLUT Program
int main() glutInitDisplayMode(GLUT_SINGLE
GLUT_RGB) glutCreateWindow(First GLUT
program) init() glutDisplayFunc(myDisplay)
glutMainLoop() return 0

• Set up GLUT with RGB mode and single buffer
• Create a GLUT window this requires that you
  specify a display callback with glutDisplayFunc
• glutMainLoop starts the GLUT event handler
  transfers control of the program to GLUT

5
Simple GLUT Program the display callback
void display() glClear (GL_COLOR_BUFFER_BIT)
glColor3f(1.0f, 1.0f, 1.0f) glBegin(GL_QUADS)
glVertex3d(1.0, 1.0, 0.0) glVertex3d(-1.0,
1.0, 0.0) glVertex3d(-1.0, -1.0,
0.0) glVertex3f(1.0, -1.0, 0.0) glEnd()

• This is where most of your openGL functions will
  be called
• In this example
• Clear the screen (or clear the frame buffer)
• Set the drawing color to white
• Draw a quad primitive with the specified vertices

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Simple GLUT program openGL initialization
void init() glClearColor(0.0f, 0.0f, 0.0f,
0.0f) glOrtho(-2, 2, -2, 2, -2, 2)

• Some OpenGL functions associated with setting up
  initial states only need to be called once in
  most programs. It is useful to place these in a
  separate initialization function.
• E.g.
• Set the clear color (the background) to black
• Tell OpenGL to use Orthographic projection with a
  bounding box defined by
• (xmin, xmax, ymin, ymax, zmin, zmax)(-2, 2, -2,
  2, -2, 2)

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GLUT

• OpenGL designed to be windows system independent
• Windows system operations e.g. creating a
  rendering window and handling window system
  events are left to native window system to define
• Learning native system API can be quite difficult
• GLUT is a system independent interface between
  for OpenGL programming
• It is designed to be simple and yet still meet
  the needs of useful OpenGL programs

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GLUT design philosophy

• GLUT requires very few routines to display a
  graphics scene rendered using OpenGL
• Like OpenGL the GLUT API is stateful and most
  initial states are predefined with defaults that
  are reasonable for simple programs
• The API is as much as possible windows system
  independent
• GLUT routines are logically organized into
  several sub-APIs according to their functionality

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GLUT sub-APIs

• Initialisation
• Command line processing, window system
  initialisation initial window state
• Beginning Event Processing
• Enter event processing loop
• Window Management
• Overlay Management
• Menu Management

• Callback Registration
• Registers procedures which will be called by GLUT
  event processing loop
• Color Index ColorMap management
• State Retrieval
• Font Rendering
• Geometric Shape Rendering

10
Conventions

• GLUT coordinates are expressed in pixels with
  (0,0) as the upper-left
• In most GLUT routines basic types (in, char) are
  used as parameters. In routines where parameters
  are passed directly to OpenGL OpenGL types are
  used (e.g. GLfloat)
• GLUT functions are prefixed glut (e.g.
  glutInitDisplayMode)
• Constants are prefixed by GLUT_.. (e.g. GLUT_RGB)

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Initialisation
void glutInit(int argcp, char argv) void
glutInitWindowSize(int width, int height) void
glutInitWindowPosition(int y, int y) void
glutInitDisplayMode(unsigned int mode)

• glutInit initializes the GLUT library
• Display modes
• GLUT_RGBA, GLUT_RGB, GLUT_INDEX, GLUT_SINGLE,
  GLUT_DOUBLE, GLUT_ACCUM, GLUT_ALPHA, GLUT_DEPTH,
  GLUT_STENCIL, GLUT_MULTISAMPLE, GLUT_STEREO

12
Beginning Event Processing
While (TRUE) egetNextEvent() switch (e)
case (MOUSE_EVENT) call
registered MouseFunc break case
(RESIZE_EVENT) call registered
ReshapeFunc break

• void glutMainLoop(void)
• glutMainLoop enters the GLUT event processing
  loop
• Should only be called once in a GLUT program
  never returns
• Calls as necesarry any registered callbacks

13
Window Management
int glutCreateWindow(char name) void
glutPostRedisplay(void) void glutSwapBuffers(void
) void glutSetWindow(int win) int
glutGetWindow(void)

• glutCreateWindow creates a top level window
  returns window id display is actually only
  called when glutMainLoop is entered
• glutPostRedisplay marks current window as needing
  to be redisplayed

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Call Back Registration

• 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 glutIdleFunc(void (func) (void))
• void glutTimerFunc(unsigned int msecs, void
  (func) (int value), value)

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Geometric Object Rendering

• void glutSolidSphere(GLdouble radius, GLint
  slices, GLint stacks)
• void glutWireSphere(GLdouble radius, GLint
  slices, GLint stacks)
• void glutSolidCube(GLdouble size)
• void glutWireCube(GLdouble size)

20, 6
8, 20
20, 20
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GLUT References

• The full GLUT manual (PS/PDF) is available
  locally for download/viewing at
• http//isg.cs.tcd.ie/dingliaj/openGL/glut.ps
• http//isg.cs.tcd.ie/dingliaj/openGL/glut.pdf
• HTML version online
• http//reality.sgi.com/mjk_asd/spec3/spec3.html
• More GLUT info at opengl.org
• http//www.opengl.org/developers/documentation/glu
  t.html