The document describes using OpenGL and RingFreeGLUT to draw 3D graphics in Ring. It includes examples of drawing basic shapes like polygons and triangles, handling window resize events, adding keyboard input for color changes, and implementing a 3D camera that can be rotated. The examples demonstrate functions for initialization, rendering, processing user input, and managing the viewport.

1. Ring Documentation, Release 1.10
62.5 Drawing using RingOpenGL
Example:
load "freeglut.ring"
load "opengl21lib.ring"
func main
glutInit()
glutInitDisplayMode(GLUT_SINGLE)
glutInitWindowSize(800, 600)
glutInitWindowPosition(100, 10)
glutCreateWindow("RingFreeGLUT - Test 2")
glutDisplayFunc(:displayCode)
glutMainLoop()
func displaycode
glClear(GL_COLOR_BUFFER_BIT)
glColor3f(0,255,0)
glBegin(GL_POLYGON)
glVertex3f(0.0, 0.0, 0.0)
62.5. Drawing using RingOpenGL 608

2. Ring Documentation, Release 1.10
glVertex3f(0.5, 0.0, 0.0)
glVertex3f(0.5, 0.5, 0.0)
glVertex3f(0.0, 0.5, 0.0)
glEnd()
glColor3f(255,0,0)
glBegin(GL_POLYGON)
glVertex3f(0.0, 0.0, 0.0)
glVertex3f(0.5, 0.0, 0.0)
glVertex3f(-0.5,- 1, 0.0)
glVertex3f(0.0, -1, 0.0)
glEnd()
glColor3f(0,0,255)
glBegin(GL_POLYGON)
glVertex3f(0.0, 0.0, 0.0)
glVertex3f(-0.5, 0.0, 0.0)
glVertex3f(-0.5,- 0.5, 0.0)
glVertex3f(0.0, -0.5, 0.0)
glEnd()
glFlush()
Screen Shot
62.5. Drawing using RingOpenGL 609

3. Ring Documentation, Release 1.10
62.6 The First Triangle
Example:
load "freeglut.ring"
load "opengl21lib.ring"
func main
glutInit()
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA)
glutInitWindowSize(320,320)
glutInitWindowPosition(100, 10)
glutCreateWindow("RingFreeGLUT - Test 3")
glutDisplayFunc(:renderScene)
glutMainLoop()
func renderScene
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
glBegin(GL_TRIANGLES)
glVertex3f(-0.5,-0.5,0.0)
glVertex3f(0.5,0.0,0.0)
glVertex3f(0.0,0.5,0.0)
glEnd()
glutSwapBuffers()
Screen Shot
62.6. The First Triangle 610

4. Ring Documentation, Release 1.10
62.7 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)
62.7. Window Resize Event 611

5. Ring Documentation, Release 1.10
// Get Back to the Modelview
glMatrixMode(GL_MODELVIEW)
62.8 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()
62.8. Triangle Rotation 612

6. Ring Documentation, Release 1.10
// 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
62.9 Keyboard Events and Colors
Example:
load "freeglut.ring"
load "opengl21lib.ring"
62.9. Keyboard Events and Colors 613

7. Ring Documentation, Release 1.10
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
62.9. Keyboard Events and Colors 614

8. Ring Documentation, Release 1.10
// (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
62.9. Keyboard Events and Colors 615

9. Ring Documentation, Release 1.10
62.10 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)
62.10. The Camera 616

10. Ring Documentation, Release 1.10
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
62.10. The Camera 617