OpenGL

1
OpenGL

• Basics

2
Header files

• include ltgl.hgt
• Raw OpenGL calls
• include ltglu.hgt
• Includes commonly requested things
• Shapes (teapots, cubes, spheres)
• include ltglut.h gt
• Includes windowing capabilities
• glut.h includes glu.h and gl.h

3
Creating a Window

• int main (int argc, char argv)
• // Initialize OpenGL
• glutInit (argc, argv)
• // Create a window
• glutInitWindowSize (500, 500)
• glutCreateWindow (Title)
• //Note still need a display function

4
Other things you may want(when initializing)

• glClearColor (0.0, 0.0, 0.0, 0.0)
• glInitWindowPosition( )
• glInitDisplayMode ( )
• GLUT_RGB
• GLUT_RGBA
• GLUT_SINGLE
• GLUT_DOUBLE (for animation)
• GLUT_DEPTH (for 3D stuff)

5
Basic OpenGL Architecture

• There is a main
• There is an even t loop
• There are a series of callbacks
• Draw/paint
• Idle function (glutIdleFunc)
• Key pressed (glutKeyboardFunc)
• Mouse (glutMouseFunc)
• Mouse movement (glutPassiveMotionFunc)

6
Event Loop

• void display ( )
• // Draw stuff
• int main (int argc, char argv)
• // Initialize OpenGL
• glutInit (argc, argv)
• // Create a window
• glutCreateWindow (Title)
• // Tell OpenGL which is the drawing function
• glutDisplayFunc (display)
• // Start the event loop
• glutMainLoop()

7
2D Drawing

• Typically uses glBegin and glEnd
• Usually clear the previous drawing first
• Example
• glClear (GL_COLOR_BUFFER_BIT)
• glBegin(GL_POLYGON)
• glVertex2f(-0.5, -0.5)
• glVertex2f(-0.5, 0.5)
• glVertex2f(0.5, 0.5)
• glVertex2f(0.5, -0.5)
• glEnd( )
• glFlush( )

8
glBegin

• Takes an enumeration type
• GL_POINTS (points)
• GL_LINES (two points per line)
• GL_LINE_STRIP (connecting points)
• GL_LINE_LOOP (enclosed points)
• GL_POLYGON (as seen before)
• glLineWidth (2.0)
• glLineStipple (0xcccc)

9
Enable/Disabling Features

• Use glEnable (type)
• glEnable (GL_LINE_STIPPLE)
• glEnable (GL_DEPTH_TEST)
• glEnable (GL_LIGHTING)

10
Note About gl Calls

• Usually specify the number and type of arguments
• glVertex2f (2 arguments of type float)
• glVertex3f (3 arguments of type float)
• glVertex3i (3 arguments of type int)
• General format glVertex234sifd

11
PolygonMode(not super-important)

• What weve been drawing has 2 faces (front and
  back)
• Drawing counter-clockwise is front
• Drawing clockwise is back
• glPolygonMode (GL_FRONT_AND_BACK, GL_FILL)
• Have option to not draw the back faces
• glCullFace ( )
• GL_FRONT
• GL_BACK
• GL_FRONT_AND_BACK

12
Setting Colors

• void glColor3bifd(r, g, b)
• Example
• void display ()
• glClear (GL_COLOR_BUFFER_BIT)
• glBegin(GL_POLYGON)
• glColor3f (1.0, 0.0, 0.0)
• glVertex2f(-0.5, -0.5)
• glColor3f (0.0, 1.0, 0.0)
• glVertex2f(-0.5, 0.5)
• glColor3f (0.0, 0.0, 1.0)
• glVertex2f(0.5, 0.5)
• glColor3f (1.0, 1.0, 1.0)
• glVertex2f(0.5, -0.5)
• glEnd( )
• glFlush( )

13
gluOrtho2D(not super-important)

• Before, we drew with a window size of -1 to 1
• gluOrtho2D redefines the coordinate system in 2D
• Scale youre working in
• Example
• gluOrtho2D(-5, 5, -5, 5)

14
The Viewport(again, not super-important)

• Restrict OpenGL to drawing in only part of the
  window (divides the window)
• void glViewport (int x, int y, int w, int h)
• Default viewport is entire window

15
Intro to the Matrix Stack

• Matrices define
• Translations
• Rotations
• Scaling
• Skewing
• We can build a matrix stack that contains a
  series of matrix operations
• A clear matrix is called the identity matrix

16
Pushing and Popping

• To add a matrix to the stack, glPushMatrix()
• To remove a matrix from the stack, glPopMatrix()

17
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

18
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Identity
19
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Identity
20
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Translate
Identity
21
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Translate
Identity
22
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Identity
Translate
Identity
23
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Translate
Identity
Translate
Identity
24
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Translate
Identity
25
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Translate
Identity
26
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Rotate
Translate
Identity
27
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Translate
Identity
28
Example

• glLoadIdentity()
• glPushMatrix()
• glTranslatef ()
• glPushMatrix()
• glLoadIdentity()
• glTranslate ()
• glPopMatrix()
• glPushMatrix()
• glRotatef ()
• glPopMatrix()
• glPopMatrix()

Identity
29
Model-View vs Projection

• We have two coordinate systems
• Model-view
• Rotation and translation of the world
• Projection
• How we are viewing this world
• Changing
• Set the matrix mode (glMatrixMode)
• Load the identity matrix (glLoadIdentity)
• Alter the matrix (gluOrtho2D)

30
Simple 2D Animation

• include ltGL/glut.hgt
• float degree 0.5f
• void display ()
• glClear (GL_COLOR_BUFFER_BIT)
• glMatrixMode (GL_MODELVIEW)
• glPushMatrix()
• glRotatef (degree, 1.0f, 0.0f, 0.0f)
• glRotatef (degree2, 0.0, 1.0f, 0.0f)
• glBegin(GL_POLYGON)
• glColor3f (1.0, 0.0, 0.0)
• glVertex3f(-0.5, -0.5, 0.0)
• glColor3f (0.0, 1.0, 0.0)
• glVertex3f(-0.5, 0.5, 0.0)
• glColor3f (0.0, 0.0, 1.0)
• glVertex3f(0.5, 0.5, 0.0)
• glColor3f (1.0, 1.0, 1.0)
• glVertex3f(0.5, -0.5, 0.0)
• glEnd( )

31
A Peek at 3D

• include ltGL/glut.hgt
• GLfloat light_position 100.0f, 100.0f,
  100.0f, 0.0f
• GLfloat diffuse_light 0.9f, 0.9, 0.9f,
  0.0f
• void display ()
• glClear (GL_COLOR_BUFFER_BIT
  GL_DEPTH_BUFFER_BIT)
• glPushMatrix()
• glTranslatef (0.0f, 0.0f, -10.f)
• glutSolidTeapot(2.0)
• glPopMatrix()
• glFlush()
• glutSwapBuffers()
• int main (int argv, char argc)
• glutInit (argv, argc)
• glutInitDisplayMode(GLUT_DOUBLE GLUT_RGBA
  GLUT_DEPTH)
• glutCreateWindow ("Bob")
• glutDisplayFunc (display)