This document describes code for rendering a 3D scene with OpenGL that includes: - Drawing a snowman model with spheres, cones, and scaling - Rendering 36 snowmen on a ground plane using loops - Camera movement with keyboard controls - Mouse camera rotation - Popup menus for color, scaling, and rendering options - Menu callback functions to handle selection

1. Ring Documentation, Release 1.7
// 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()
57.11. Mouse Events 562

2. Ring Documentation, Release 1.7
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
57.11. Mouse Events 563

3. Ring Documentation, Release 1.7
if button = GLUT_LEFT_BUTTON
// when the button is released
if state = GLUT_UP
angle += deltaAngle
xOrigin = -1
else
// state = GLUT_DOWN
xOrigin = xx
ok
fflush(stdout)
ok
func main
// init GLUT and create window
glutInit()
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA)
glutInitWindowPosition(100,100)
glutInitWindowSize(320,320)
glutCreateWindow("RingFreeGLUT - Test 9")
// register callbacks
glutDisplayFunc(:renderScene)
glutReshapeFunc(:changeSize)
glutIdleFunc(:renderScene)
glutIgnoreKeyRepeat(1)
glutKeyboardFunc(:processNormalKeys)
glutSpecialFunc(:pressKey)
glutSpecialUpFunc(:releaseKey)
// here are the two new functions
glutMouseFunc(:mouseButton)
glutMotionFunc(:mouseMove)
// OpenGL init
glEnable(GL_DEPTH_TEST)
// enter GLUT event processing cycle
glutMainLoop()
57.12 Menu 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
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4. Ring Documentation, Release 1.7
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
xOrigin = -1
// Constant definitions for Menus
// for RingFreeGLUT - We must have different ID for each menu item
C_RED = 1
C_GREEN = 2
C_BLUE = 3
C_ORANGE = 4
C_FILL = 5
C_LINE = 6
C_SHRINK = 7
C_NORMAL = 8
// Pop up menu identifiers
fillMenu= 0
shrinkMenu= 0
mainMenu=0
colorMenu=0
// color for the nose
red = 1.0 blue=0.5 green=0.5
// scale of snowman
scale = 1.0
// menu status
menuFlag = 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)
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5. Ring Documentation, Release 1.7
// Set the correct perspective.
gluPerspective(45.0, ratio, 0.1, 100.0)
// Get Back to the Modelview
glMatrixMode(GL_MODELVIEW)
func drawSnowMan
glScalef(scale, scale, scale)
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(red, green, blue)
glRotatef(0.0,1.0, 0.0, 0.0)
glutSolidCone(0.08,0.5,10,2)
glColor3f(1.0, 1.0, 1.0)
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)
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6. Ring Documentation, Release 1.7
// 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, 0.0, j * 10.0)
drawSnowMan()
glPopMatrix()
next
next
glutSwapBuffers()
// -----------------------------------
// KEYBOARD
// -----------------------------------
func processNormalKeys
key = glutEventKey()
xx = glutEventX()
yy = glutEventY()
glutSetMenu(mainMenu)
switch key
on 27
glutDestroyMenu(mainMenu)
glutDestroyMenu(fillMenu)
glutDestroyMenu(colorMenu)
glutDestroyMenu(shrinkMenu)
shutdown()
on 's'
if not menuFlag
glutChangeToSubMenu(2,"Shrink",shrinkMenu)
ok
on 'c'
if not menuFlag
glutChangeToSubMenu(2,"Color",colorMenu)
ok
off
if key = 27
shutdown()
ok
func pressKey
key = glutEventKey()
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7. Ring Documentation, Release 1.7
xx = glutEventX()
yy = glutEventY()
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
// -----------------------------------
// MOUSE
// -----------------------------------
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
if button = GLUT_LEFT_BUTTON
// when the button is released
if state = GLUT_UP
angle += deltaAngle
xOrigin = -1
else
// state = GLUT_DOWN
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8. Ring Documentation, Release 1.7
xOrigin = xx
ok
ok
// -----------------------------------
// MENUS
// -----------------------------------
func processMenuStatus
status = glutEventStatus()
xx = glutEventX()
yy = glutEventY()
if status = GLUT_MENU_IN_USE
menuFlag = 1
else
menuFlag = 0
ok
func processMainMenu
// nothing to do in here
// all actions are for submenus
func processFillMenu
option = glutEventValue()
switch option
on C_FILL
glPolygonMode(GL_FRONT, GL_FILL)
on C_LINE
glPolygonMode(GL_FRONT, GL_LINE)
off
func processShrinkMenu
option = glutEventValue()
switch option
on C_SHRINK
scale = 0.5
on C_NORMAL
scale = 1.0
off
func processColorMenu
option = glutEventValue()
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9. Ring Documentation, Release 1.7
switch option
on C_RED
red = 1.0
green = 0.0
blue = 0.0
on C_GREEN
red = 0.0
green = 1.0
blue = 0.0
on C_BLUE
red = 0.0
green = 0.0
blue = 1.0
on C_ORANGE
red = 1.0
green = 0.5
blue = 0.5
off
func createPopupMenus
shrinkMenu = glutCreateMenu(:processShrinkMenu)
glutAddMenuEntry("Shrink",C_SHRINK)
glutAddMenuEntry("NORMAL",C_NORMAL)
fillMenu = glutCreateMenu(:processFillMenu)
glutAddMenuEntry("Fill",C_FILL)
glutAddMenuEntry("Line",C_LINE)
colorMenu = glutCreateMenu(:processColorMenu)
glutAddMenuEntry("Red",C_RED)
glutAddMenuEntry("Blue",C_BLUE)
glutAddMenuEntry("Green",C_GREEN)
glutAddMenuEntry("Orange",C_ORANGE)
mainMenu = glutCreateMenu(:processMainMenu)
glutAddSubMenu("Polygon Mode", fillMenu)
glutAddSubMenu("Color", colorMenu)
// attach the menu to the right button
glutAttachMenu(GLUT_RIGHT_BUTTON)
// this will allow us to know if the menu is active
glutMenuStatusFunc(:processMenuStatus)
// -----------------------------------
// MAIN
// -----------------------------------
func main
// init GLUT and create window
glutInit()
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA)
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10. Ring Documentation, Release 1.7
glutInitWindowPosition(100,100)
glutInitWindowSize(320,320)
glutCreateWindow("RingFreeGLUT - Test 10")
// register callbacks
glutDisplayFunc(:renderScene)
glutReshapeFunc(:changeSize)
glutIdleFunc(:renderScene)
glutIgnoreKeyRepeat(1)
glutKeyboardFunc(:processNormalKeys)
glutSpecialFunc(:pressKey)
glutSpecialUpFunc(:releaseKey)
// here are the two new functions
glutMouseFunc(:mouseButton)
glutMotionFunc(:mouseMove)
// OpenGL init
glEnable(GL_DEPTH_TEST)
glEnable(GL_CULL_FACE)
// init Menus
createPopupMenus()
// enter GLUT event processing cycle
glutMainLoop()
Screen Shot
57.13 Using Fonts
Example:
57.13. Using Fonts 571