This document contains examples of Ring code for implementing camera controls and mouse interactions in OpenGL programs using the RingFreeGLUT library. It shows how to update the camera position and direction based on key presses and mouse movement. Functions are provided to handle window resizing, rendering the scene from the camera's perspective, and processing input events for keys and mouse buttons.

1. Ring Documentation, Release 1.8
58.10 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)
58.10. The Camera 571

2. Ring Documentation, Release 1.8
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
58.10. The Camera 572

3. Ring Documentation, Release 1.8
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)
58.10. The Camera 573

4. Ring Documentation, Release 1.8
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
58.10. The Camera 574

5. Ring Documentation, Release 1.8
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)
58.10. The Camera 575

6. Ring Documentation, Release 1.8
func computePos deltaMove
x += deltaMove * lx * 0.1
z += deltaMove * lz * 0.1
func computeDir deltaAngle
angle += deltaAngle
lx = sin(angle)
lz = -cos(angle)
func renderScene
if deltaMove
computePos(deltaMove)
ok
if deltaAngle
computeDir(deltaAngle)
ok
// Clear Color and Depth Buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
// Reset transformations
glLoadIdentity()
// Set the camera
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 pressKey
key = glutEventKey()
xx = glutEventX()
58.10. The Camera 576

7. Ring Documentation, Release 1.8
yy = glutEventY()
switch key
on GLUT_KEY_LEFT
deltaAngle = -0.01
on GLUT_KEY_RIGHT
deltaAngle = 0.01
on GLUT_KEY_UP
deltaMove = 0.5
on GLUT_KEY_DOWN
deltaMove = -0.5
off
func releaseKey
key = glutEventKey()
switch key
on GLUT_KEY_LEFT
deltaAngle = 0.0
on GLUT_KEY_RIGHT
deltaAngle = 0.0
on GLUT_KEY_UP
deltaMove = 0
on GLUT_KEY_DOWN
deltaMove = 0
off
func main
// init GLUT and create window
glutInit()
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA)
glutInitWindowPosition(100,100)
glutInitWindowSize(320,320)
glutCreateWindow("RingFreeGLUT - Test 8")
// register callbacks
glutDisplayFunc(:renderScene)
glutReshapeFunc(:changeSize)
glutIdleFunc(:renderScene)
glutSpecialFunc(:pressKey)
// here are the new entries
glutIgnoreKeyRepeat(1)
glutSpecialUpFunc(:releaseKey)
// OpenGL init
glEnable(GL_DEPTH_TEST)
// enter GLUT event processing cycle
glutMainLoop()
58.10. The Camera 577

8. Ring Documentation, Release 1.8
58.11 Mouse Events
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
deltaMove = 0.0
xOrigin = -1
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)
58.11. Mouse Events 578

9. Ring Documentation, Release 1.8
// 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)
func computePos deltaMove
x += deltaMove * lx * 0.1
z += deltaMove * lz * 0.1
func renderScene
if deltaMove
computePos(deltaMove)
ok
// Clear Color and Depth Buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
// Reset transformations
glLoadIdentity()
// Set the camera
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()
58.11. Mouse Events 579

10. Ring Documentation, Release 1.8
next
next
glutSwapBuffers()
func processNormalKeys
key = glutEventKey()
if key = 27
shutdown()
ok
func pressKey
key = glutEventKey()
switch key
on GLUT_KEY_UP
deltaMove = 0.5
on GLUT_KEY_DOWN
deltaMove = -0.5
off
func releaseKey
key = glutEventKey()
switch key
on GLUT_KEY_UP
deltaMove = 0
on GLUT_KEY_DOWN
deltaMove = 0
off
func mouseMove
xx = glutEventX()
yy = glutEventY()
// this will only be true when the left button is down
if xOrigin >= 0
// update deltaAngle
deltaAngle = (xx - xOrigin) * 0.001
// update camera's direction
lx = sin(angle + deltaAngle)
lz = -cos(angle + deltaAngle)
ok
func mouseButton
button = glutEventButton()
state = glutEventState()
xx = glutEventX()
yy = glutEventY()
// only start motion if the left button is pressed
58.11. Mouse Events 580