The document describes how to handle window resize events in OpenGL. It provides code for a function called changeSize() that gets called on window resize. This function updates the viewport and projection matrix to adjust for the new window size and aspect ratio, preventing distortion. It also handles preventing a divide by zero if the window width becomes zero.

1. Ring Documentation, Release 1.5.3
54.7 Window Resize Event
Example:
load "freeglut.ring"
load "opengl21lib.ring"
func main
// init GLUT and create window
glutInit()
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA)
glutInitWindowPosition(100,100)
glutInitWindowSize(320,320)
glutCreateWindow("RingFreeGLUT - Test 4")
glutDisplayFunc(:renderScene)
glutReshapeFunc(:changeSize)
glutMainLoop()
func renderScene
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
glBegin(GL_TRIANGLES)
glVertex3f(-2,-2,-5.0)
glVertex3f(2,0.0,-5.0)
glVertex3f(0.0,2,-5.0)
glEnd()
glutSwapBuffers()
func changesize
h = glutEventHeight()
w = glutEventWidth()
// Prevent a divide by zero, when window is too short
// (you cant make a window of zero width).
if (h = 0)
h = 1
ok
ratio = w * 1.0 / h
// Use the Projection Matrix
glMatrixMode(GL_PROJECTION)
// Reset Matrix
glLoadIdentity()
// Set the viewport to be the entire window
glViewport(0, 0, w, h)
// Set the correct perspective.
gluPerspective(45,ratio,1,100)
54.7. Window Resize Event 505

2. Ring Documentation, Release 1.5.3
// Get Back to the Modelview
glMatrixMode(GL_MODELVIEW)
54.8 Triangle Rotation
Example:
load "freeglut.ring"
load "opengl21lib.ring"
angle = 0
func main
// init GLUT and create window
glutInit()
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA)
glutInitWindowPosition(100,100)
glutInitWindowSize(320,320)
glutCreateWindow("RingFreeGLUT - Test 5")
glutDisplayFunc(:renderScene)
glutReshapeFunc(:changeSize)
glutIdleFunc(:renderScene)
glutMainLoop()
func renderScene
// Clear Color and Depth Buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
// Reset transformations
glLoadIdentity()
// Set the camera
gluLookAt( 0.0, 0.0, 10.0,
0.0, 0.0, 0.0,
0.0, 1.0, 0.0)
glRotatef(angle, 0.0, 1.0, 0.0)
glBegin(GL_TRIANGLES)
glVertex3f(-2.0,-2.0, 0.0)
glVertex3f( 2.0, 0.0, 0.0)
glVertex3f( 0.0, 2.0, 0.0)
glEnd()
angle+=0.1
glutSwapBuffers();
func changesize
h = glutEventHeight()
w = glutEventWidth()
54.8. Triangle Rotation 506

3. Ring Documentation, Release 1.5.3
// Prevent a divide by zero, when window is too short
// (you cant make a window of zero width).
if (h = 0)
h = 1
ok
ratio = w * 1.0 / h
// Use the Projection Matrix
glMatrixMode(GL_PROJECTION)
// Reset Matrix
glLoadIdentity()
// Set the viewport to be the entire window
glViewport(0, 0, w, h)
// Set the correct perspective.
gluPerspective(45,ratio,1,100)
// Get Back to the Modelview
glMatrixMode(GL_MODELVIEW)
Screen Shot
54.9 Keyboard Events and Colors
Example:
load "freeglut.ring"
load "opengl21lib.ring"
54.9. Keyboard Events and Colors 507

4. Ring Documentation, Release 1.5.3
angle = 0
red=1.0
blue=1.0
green=1.0
func main
// init GLUT and create window
glutInit()
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA)
glutInitWindowPosition(100,100)
glutInitWindowSize(320,320)
glutCreateWindow("RingFreeGLUT - Test 6")
glutDisplayFunc(:renderScene)
glutReshapeFunc(:changeSize)
glutIdleFunc(:renderScene)
// here are the new entries
glutKeyboardFunc(:processNormalKeys)
glutSpecialFunc(:processSpecialKeys)
glutMainLoop()
func renderScene
// Clear Color and Depth Buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
// Reset transformations
glLoadIdentity()
// Set the camera
gluLookAt( 0.0, 0.0, 10.0,
0.0, 0.0, 0.0,
0.0, 1.0, 0.0)
glRotatef(angle, 0.0, 1.0, 0.0)
glColor3f(red,green,blue);
glBegin(GL_TRIANGLES)
glVertex3f(-2.0,-2.0, 0.0)
glVertex3f( 2.0, 0.0, 0.0)
glVertex3f( 0.0, 2.0, 0.0)
glEnd()
angle+=0.1
glutSwapBuffers();
func changesize
h = glutEventHeight()
w = glutEventWidth()
// Prevent a divide by zero, when window is too short
54.9. Keyboard Events and Colors 508

5. Ring Documentation, Release 1.5.3
// (you cant make a window of zero width).
if (h = 0)
h = 1
ok
ratio = w * 1.0 / h
// Use the Projection Matrix
glMatrixMode(GL_PROJECTION)
// Reset Matrix
glLoadIdentity()
// Set the viewport to be the entire window
glViewport(0, 0, w, h)
// Set the correct perspective.
gluPerspective(45,ratio,1,100)
// Get Back to the Modelview
glMatrixMode(GL_MODELVIEW)
func processNormalKeys
key = GLUTEventKey()
if key = 27
shutdown()
ok
func processSpecialKeys
key = GLUTEventKey()
switch key
on GLUT_KEY_F1
red = 1.0
green = 0.0
blue = 0.0
on GLUT_KEY_F2
red = 0.0
green = 1.0
blue = 0.0
on GLUT_KEY_F3
red = 0.0
green = 0.0
blue = 1.0
off
Screen Shot
54.9. Keyboard Events and Colors 509

6. Ring Documentation, Release 1.5.3
54.10 The Camera
Example:
load "freeglut.ring"
load "opengl21lib.ring"
// angle of rotation for the camera direction
angle=0.0
// actual vector representing the camera's direction
lx=0.0
lz=-1.0
// XZ position of the camera
x=0.0
z=5.0
func drawSnowMan
glColor3f(1.0, 1.0, 1.0)
// Draw Body
glTranslatef(0.0 ,0.75, 0.0)
glutSolidSphere(0.75,20,20)
// Draw Head
glTranslatef(0.0, 1.0, 0.0)
glutSolidSphere(0.25,20,20)
// Draw Eyes
glPushMatrix()
glColor3f(0.0,0.0,0.0)
glTranslatef(0.05, 0.10, 0.18)
54.10. The Camera 510

7. Ring Documentation, Release 1.5.3
glutSolidSphere(0.05,10,10)
glTranslatef(-0.1, 0.0, 0.0)
glutSolidSphere(0.05,10,10)
glPopMatrix()
// Draw Nose
glColor3f(1.0, 0.5 , 0.5)
glutSolidCone(0.08,0.5,10,2)
func changeSize
w = glutEventWidth()
h = glutEventHeight()
// Prevent a divide by zero, when window is too short
// (you cant make a window of zero width).
if h = 0
h = 1
ok
ratio = w * 1.0 / h
// Use the Projection Matrix
glMatrixMode(GL_PROJECTION)
// Reset Matrix
glLoadIdentity()
// Set the viewport to be the entire window
glViewport(0, 0, w, h)
// Set the correct perspective.
gluPerspective(45.0, ratio, 0.1, 100.0);
// Get Back to the Modelview
glMatrixMode(GL_MODELVIEW)
func processNormalKeys
key = glutEventKey()
if key = 27
shutdown()
ok
func renderScene
// Clear Color and Depth Buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
// Reset transformations
glLoadIdentity()
// Set the camera
54.10. The Camera 511

8. Ring Documentation, Release 1.5.3
gluLookAt( x, 1.0, z,
x+lx, 1.0, z+lz,
0.0, 1.0, 0.0)
// Draw ground
glColor3f(0.9, 0.9, 0.9)
glBegin(GL_QUADS)
glVertex3f(-100.0, 0.0, -100.0)
glVertex3f(-100.0, 0.0, 100.0)
glVertex3f( 100.0, 0.0, 100.0)
glVertex3f( 100.0, 0.0, -100.0)
glEnd()
// Draw 36 SnowMen
for i = -3 to 2
for j=-3 to 2
glPushMatrix()
glTranslatef(i*10.0,0,j * 10.0)
drawSnowMan()
glPopMatrix()
next
next
glutSwapBuffers()
func processSpecialKeys
key = glutEventKey()
fraction = 0.1
switch key
on GLUT_KEY_LEFT
angle -= 0.01
lx = sin(angle)
lz = -cos(angle)
on GLUT_KEY_RIGHT
angle += 0.01
lx = sin(angle)
lz = -cos(angle)
on GLUT_KEY_UP
x += lx * fraction
z += lz * fraction
on GLUT_KEY_DOWN
x -= lx * fraction
z -= lz * fraction
off
func main
// init GLUT and create window
glutInit()
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA)
54.10. The Camera 512

9. Ring Documentation, Release 1.5.3
glutInitWindowPosition(100,100)
glutInitWindowSize(320,320)
glutCreateWindow("RingFreeGLUT - Test 7")
// register callbacks
glutDisplayFunc(:renderScene)
glutReshapeFunc(:changeSize)
glutIdleFunc(:renderScene)
glutKeyboardFunc(:processNormalKeys)
glutSpecialFunc(:processSpecialKeys)
// OpenGL init
glEnable(GL_DEPTH_TEST)
// enter GLUT event processing cycle
glutMainLoop()
Screen Shot
Another Example:
load "freeglut.ring"
load "opengl21lib.ring"
// angle of rotation for the camera direction
angle = 0.0
// actual vector representing the camera's direction
lx=0.0 lz=-1.0
// XZ position of the camera
x=0.0 z=5.0
// the key states. These variables will be zero
//when no key is being presses
deltaAngle = 0.0
54.10. The Camera 513

10. Ring Documentation, Release 1.5.3
deltaMove = 0
func changeSize
w = glutEventWidth()
h = glutEventHeight()
// Prevent a divide by zero, when window is too short
// (you cant make a window of zero width).
if h = 0
h = 1
ok
ratio = w * 1.0 / h
// Use the Projection Matrix
glMatrixMode(GL_PROJECTION)
// Reset Matrix
glLoadIdentity()
// Set the viewport to be the entire window
glViewport(0, 0, w, h)
// Set the correct perspective.
gluPerspective(45.0, ratio, 0.1, 100.0)
// Get Back to the Modelview
glMatrixMode(GL_MODELVIEW)
func drawSnowMan
glColor3f(1.0, 1.0, 1.0)
// Draw Body
glTranslatef(0.0 ,0.75, 0.0)
glutSolidSphere(0.75,20,20)
// Draw Head
glTranslatef(0.0, 1.0, 0.0)
glutSolidSphere(0.25,20,20)
// Draw Eyes
glPushMatrix()
glColor3f(0.0,0.0,0.0)
glTranslatef(0.05, 0.10, 0.18)
glutSolidSphere(0.05,10,10)
glTranslatef(-0.1, 0.0, 0.0)
glutSolidSphere(0.05,10,10)
glPopMatrix()
// Draw Nose
glColor3f(1.0, 0.5 , 0.5)
glRotatef(0.0,1.0, 0.0, 0.0)
glutSolidCone(0.08,0.5,10,2)
54.10. The Camera 514