Rotated Ellipses

1
Rotated Ellipses

• Hard!
• Many APIs dont support non-axis aligned
  ellipses
• DaSilvas Masters Thesis, Brown University, 1989
• http//www.codeguru.com/gdi/ellipse.shtml

2
OpenGL and GLUT

• CS 4451

3
What is OpenGL?

• A software interface to graphics hardware
• Industry Standard
• Platform independent (unlike Direct3D)
• Low level
• No modeling functions
• Simple geometric primitives
• Points, lines, polygons

4
Drivers

• Windows ships with OpenGL 1.1 software drivers
• Current 3D graphics cards should ship with OpenGL
  1.2
• Linux - Mesa, a work-alike 3D graphics library

5
Complementary Libraries

• OpenGL Utility Library (GLU)
• quadratic surfaces, NURBS curves, etc.
• Open Inventor (a high level OO 3D library)
• Windowing?
• X window interface library (GLX)
• MS Windows window interface library (WGL)
• Macintosh window interface library (AGL)
• GL Auxiliary library (GLAUX)
• OpenGL Utility Toolkit (GLUT)

6
Other Windowing Libraries

• All you need for OpenGL is an OpenGL context in
  which to draw

• VisualBasic
• Win32
• Aqua
• Tcl/Tk
• Java
• FLTK
• WX Windows
• QT
• GTK

7
Books

• Mason Woo, Jackie Neider, Tom Davis, Dave
  Shreiner, OpenGL Architecture Review Board,
  OpenGL(R) Programming Guide The Official Guide
  to Learning OpenGL, Version 1.2, ISBN 0201604582,
  AKA the redbook
• Richard S. Wright Jr., Michael R. Sweet, OpenGL
  SuperBible, Second Edition (2nd Edition), ISBN
  1571691642

8
Websites

• Older version of redbook (OpenGL 1.1)
• http//ask.ii.uib.no/ebt-bin/nph-dweb/dynaweb/
• SGI_Developer/OpenGL_PG/
• OpenGL website
• http//www.opengl.org
• SGI OpenGL
• http//www.sgi.com/software/opengl

9
Simplified Pipeline

• 1. Construct Shapes from Geometric Primitives,
  thereby creating mathematical descriptions of
  objects (points, lines, polygons, images, and
  bitmaps)
• 2. Arrange the objects in 3D space and select
  the desired viewpoint for viewing the scene

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Simplified Pipeline (cont.)

• 3. Calculate the color of all the objects.
  Either by assignment by the program, lighting
  conditions, texture mapping, or a combination
• 4. Convert the mathematical description of
  objects and associated color information to
  pixels on the screen (rasterization)

11
Client/Server

• For X Windows
• The program that issues drawing commands is the
  client
• The computer that does receives the commands and
  does the drawing is the server

12
State Machine

• The OpenGL server is a state machine
• Retains state (background color for example)
  until explicitly changed
• Many state variables are modes enabled by
  glEnable or glDisable (fog, lighting, depthtest,
  etc.)
• Other state variables include view and projection
  transforms

13
Programming

• Quick look at code
• Include files
• Library files
• Setting up windows
• Display function
• First running example

14
Example Code

• include ltwhateverYouNeed.hgt
• main()
• InitializeAWindowPlease()
• glClearColor (0.0, 0.0, 0.0, 0.0)
• glClear (GL_COLOR_BUFFER_BIT)
• glColor3f (1.0, 1.0, 1.0)
• glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0)

• glBegin(GL_POLYGON)
• glVertex3f (0.25, 0.25, 0.0)
• glVertex3f (0.75, 0.25, 0.0)
• glVertex3f (0.75, 0.75, 0.0)
• glVertex3f (0.25, 0.75, 0.0)
• glEnd()
• glFlush()
• UpdateTheWindowCheckForEvents()

15
GL Functions and Datatypes
16
Include Files

• Include files
• include ltGL/gl.hgt
• include ltGL/glu.hgt
• or
• include ltGL/glut.hgt
• sometimes glut.h is placed in the directory above
  (some Unix).
• include ltglut.hgt

17
Library Files

• opengl32.lib
• glu32.lib
• glut32.lib
• glaux.lib (optional)

18
Window Management

• Five tasks needed for window initialization
• glutInit(int argc, char argv)
• glutInitDisplayMode(unsigned int mode)
• glutInitWindowPosition(int x, int y)
• glutInitWindowSize(int width, int size)
• int glutCreateWindow(char string)

19
Display Callback

• The drawing function
• glutDisplayFunc(void (func)(void))
• Calling for a redraw
• glutPostRedisplay(void)

20
Main Loop

• glutMainLoop(void)
• GLUT takes over
• handles events
• calls appropriate callback functions for display
  and input events
• never exits until program ends
• you do all your work in callback functions

21
Hello World, GL

• include ltGL/gl.hgt
• include ltGL/glut.hgt
• void display(void)
• / clear all pixels /
• glClear (GL_COLOR_BUFFER_BIT)
• / draw white polygon (rectangle) with corners
  at
• (0.25, 0.25, 0.0) and (0.75, 0.75, 0.0)
• /
• glColor3f (1.0, 1.0, 1.0)
• glBegin(GL_POLYGON)
• glVertex3f (0.25, 0.25, 0.0)
• glVertex3f (0.75, 0.25, 0.0)
• glVertex3f (0.75, 0.75, 0.0)
• glVertex3f (0.25, 0.75, 0.0)
• glEnd()

• void init (void)
• / select clearing (background) color /
• glClearColor (0.0, 0.0, 0.0, 0.0)
• / initialize viewing values /
• glMatrixMode(GL_PROJECTION)
• glLoadIdentity()
• glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0)
• int main(int argc, char argv)
• glutInit(argc, argv)
• glutInitDisplayMode (GLUT_SINGLE GLUT_RGB)
• glutInitWindowSize (250, 250)
• glutInitWindowPosition (100, 100)
• glutCreateWindow ("hello")
• init ()

22
Customizing the Example

• Clearing
• Coloring
• Forcing the draw completion

23
Clearing

• Clear the screen (background color)
• glClearColor(0.0, 0.0, 0.0, 0.0)
• glClear(GL_COLOR_BUFFER_BIT)
• (later, you will need to clear the depth buffer)

24
Specifying Drawing Color

• glColor3f(Glfloat r, Glfloat g, Glfloat b)
• 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

25
glBegin and glEnd

• Drawing commands are sandwiched between glBegin
  and glEnd commands
• Can have multiple glBegin/glEnd pairs
• glBegin(GL_POLYGON)
• glVertex3f (0.25, 0.25, 0.0)
• glVertex3f (0.75, 0.25, 0.0)
• glVertex3f (0.75, 0.75, 0.0)
• glVertex3f (0.25, 0.75, 0.0)
• glEnd()

26
glBegin and glEnd (cont.)

• GL_POINTS
• individual points
• GL_LINES
• pairs of vertices as individual line segments
• GL_LINE_STRIP
• series of connected lines
• GL_LINE_LOOP
• first and last vertices connected
• GL_TRIANGLES
• triples of vertices as triangles

27
glBegin and glEnd (cont.)

• GL_TRIANGLE_STRIP
• linked strip of triangles. Reuse of vertices.
• GL_TRIANGLE_FAN
• linked fans of triangles
• GL_QUADS
• each set of 4 points forms 4 sided polygon
• GL_QUAD_STRIP
• linked strip of quadrilaterals
• GL_POLYGON
• simple convex polygon of all points

28
glBegin and glEnd (cont.)
29
glFlush

• glFlush to force gl command execution
• cleans out pipeline
• stop buffering commands for network transmission
• software renderers that do not immediately update
  the screen
• to ensure compatibility, you should have a
  glFlush at the end of each frame or scene

30
Other Event Handlers

• glutReshapeFunc(void (func)(int w, int h))
• glutKeyboardFunc(void (func)(unsigned char key,
  int x, int y))
• glutMouseFunc(void (func)(int button, int state,
  int x, int y))
• glutMotionFunc(void (func)(int x, int y))

31
GLUT.H

• Look inside GLUT (glut.h) for more cool functions
• http//www.tangent.org/brian/dict/spec3/node110.h
  tml
• IdleFunc
• TimerFunc
• menu items
• changing the cursor
• drawing text
• handling multiple windows
• built-in models

32
Animation

• Charlie Chaplin 16 frames a second
• Modern film 24 frames a second
• NTSC Video 30 frames a second
• PAL Video 25 frames a second
• limit of interactive applications
• 10 frames a second

33
Snow Day Implementation

• open_window()
• for (i 0 i lt 1000000 i)
• clear_the_window()
• draw_frame(i)
• wait_until_a_24th_of_a_second_is_over()
• complete frame is up only a fraction of a second,
  lots of flashing

34
Double Buffering

• open_window_in_double_buffer_mode()
• for (i 0 i lt 1000000 i)
• clear_the_window()
• draw_frame(i)
• swap_the_buffers()
• Hardware swapping is faster, a fully drawn
  picture is up on screen for nearly all the time

35
Animation Example

• include ltGL/gl.hgt
• include ltGL/glu.hgt
• include ltGL/glut.hgt
• include ltstdlib.hgt
• static GLfloat spin 0.0
• void init(void)
• glClearColor (0.0, 0.0, 0.0, 0.0)
• glShadeModel (GL_FLAT)
• void display(void)
• glClear(GL_COLOR_BUFFER_BIT)
• glPushMatrix()
• glRotatef(spin, 0.0, 0.0, 1.0)
• glColor3f(1.0, 1.0, 1.0)
• glRectf(-25.0, -25.0, 25.0, 25.0)
• glPopMatrix()
• glutSwapBuffers()

• void spinDisplay(void)
• spin spin 2.0
• if (spin gt 360.0)
• spin spin - 360.0
• glutPostRedisplay()
• int main(int argc, char argv)
• glutInit(argc, argv)
• glutInitDisplayMode (GLUT_DOUBLE GLUT_RGB)
• glutInitWindowSize (250, 250)
• glutInitWindowPosition (100, 100)
• glutCreateWindow (argv0)
• init ()
• glutDisplayFunc(display)
• glutReshapeFunc(reshape)
• glutMouseFunc(mouse)
• glutMainLoop()
• return 0

void reshape(int w, int h) glViewport (0, 0,
(GLsizei) w, (GLsizei) h) glMatrixMode(GL_PROJ
ECTION) glLoadIdentity() glOrtho(-50.0,
50.0, -50.0, 50.0, -1.0, 1.0)
glMatrixMode(GL_MODELVIEW) glLoadIdentity()
void mouse(int button, int state, int x, int y)
switch (button) case
GLUT_LEFT_BUTTON if (state
GLUT_DOWN) glutIdleFunc(spinDisplay)
break case GLUT_MIDDLE_BUTTON if
(state GLUT_DOWN) glutIdleFunc(NULL)
break default break
36
glOrtho

• void glOrtho(GLdouble left,
• GLdouble right,
• GLdouble bottom,
• GLdouble top,
• GLdouble near,
• GLdouble far)

37
gluPerspective()

• Perspective Transform
• To be discussed later