This document contains code for rendering a scene with OpenGL and calculating the frames per second (FPS). It defines functions for drawing a snowman, rendering text, handling keyboard input, and displaying the FPS. The main function initializes OpenGL, creates menus, registers callbacks, and enters the GLUT event loop. Code within renderScene() draws the scene, ground, and snowmen, and calculates FPS by counting frames over time.

1. Ring Documentation, Release 1.5.1
next
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, 0.0, j * 10.0)
drawSnowMan()
number = (i+3)*6+(j+3)
renderBitmapString(0.0, 0.5, 0.0,font ,""+number)
glPopMatrix()
next
next
glutSwapBuffers()
// -----------------------------------
// KEYBOARD
// -----------------------------------
func processNormalKeys
key = glutEventKey()
xx = glutEventX()
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yy = glutEventY()
switch key
on 27
glutDestroyMenu(mainMenu)
glutDestroyMenu(fillMenu)
glutDestroyMenu(colorMenu)
glutDestroyMenu(fontMenu)
Shutdown()
off
func pressKey
key = glutEventKey()
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
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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
xOrigin = xx
ok
ok
// -----------------------------------
// MENUS
// -----------------------------------
func processMenuStatus
status = glutEventStatus()
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 processFontMenu
option = glutEventValue()
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switch (option) {
on C_INT_GLUT_BITMAP_8_BY_13
font = GLUT_BITMAP_8_BY_13
on C_INT_GLUT_BITMAP_9_BY_15
font = GLUT_BITMAP_9_BY_15
on C_INT_GLUT_BITMAP_TIMES_ROMAN_10
font = GLUT_BITMAP_TIMES_ROMAN_10
on C_INT_GLUT_BITMAP_TIMES_ROMAN_24
font = GLUT_BITMAP_TIMES_ROMAN_24
on C_INT_GLUT_BITMAP_HELVETICA_10
font = GLUT_BITMAP_HELVETICA_10
on C_INT_GLUT_BITMAP_HELVETICA_12
font = GLUT_BITMAP_HELVETICA_12
on C_INT_GLUT_BITMAP_HELVETICA_18
font = GLUT_BITMAP_HELVETICA_18
off
func processColorMenu
option = glutEventValue()
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
fontMenu = glutCreateMenu(:processFontMenu)
glutAddMenuEntry("BITMAP_8_BY_13 ",C_INT_GLUT_BITMAP_8_BY_13 )
glutAddMenuEntry("BITMAP_9_BY_15",C_INT_GLUT_BITMAP_9_BY_15 )
glutAddMenuEntry("BITMAP_TIMES_ROMAN_10 ",C_INT_GLUT_BITMAP_TIMES_ROMAN_10 )
glutAddMenuEntry("BITMAP_TIMES_ROMAN_24",C_INT_GLUT_BITMAP_TIMES_ROMAN_24 )
glutAddMenuEntry("BITMAP_HELVETICA_10 ",C_INT_GLUT_BITMAP_HELVETICA_10 )
glutAddMenuEntry("BITMAP_HELVETICA_12",C_INT_GLUT_BITMAP_HELVETICA_12 )
glutAddMenuEntry("BITMAP_HELVETICA_18",C_INT_GLUT_BITMAP_HELVETICA_18 )
fillMenu = glutCreateMenu(:processFillMenu)
glutAddMenuEntry("Fill",C_FILL)
glutAddMenuEntry("Line",C_LINE)
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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)
glutAddSubMenu("Font",fontMenu)
// 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)
glutInitWindowPosition(100,100)
glutInitWindowSize(320,320)
glutCreateWindow("RingFreeGLUT - Test 11")
// 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
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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
xOrigin = -1
// Constant definitions for Menus
C_RED = 1
C_GREEN = 2
C_BLUE = 3
C_ORANGE = 4
C_FILL = 5
C_LINE = 6
// Pop up menu identifiers
fillMenu=NULL
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fontMenu=NULL
mainMenu=NULL
colorMenu=NULL
// color for the nose
red = 1.0
blue=0.5
green=0.5
// scale of snowman
scale = 1.0
// menu status
menuFlag = 0
// default font
font = GLUT_BITMAP_TIMES_ROMAN_24
C_INT_GLUT_BITMAP_8_BY_13 = 7
C_INT_GLUT_BITMAP_9_BY_15 = 8
C_INT_GLUT_BITMAP_TIMES_ROMAN_10 = 9
C_INT_GLUT_BITMAP_TIMES_ROMAN_24 = 10
C_INT_GLUT_BITMAP_HELVETICA_10 = 11
C_INT_GLUT_BITMAP_HELVETICA_12 = 12
C_INT_GLUT_BITMAP_HELVETICA_18 = 13
// width and height of the window
h = 0
w = 0
// variables to compute frames per second
frame=0
time=0
timebase=0
s = ""
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.
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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 renderBitmapString x,y,z,font,string
glRasterPos3f(x, y,z)
for c in string
glutBitmapCharacter(font,ascii(c))
next
func renderStrokeFontString x,y,z,font,string
glPushMatrix()
glTranslatef(x, y,z)
glScalef(0.002, 0.002, 0.002)
for c in string
glutStrokeCharacter(font, Ascii(c));
next
glPopMatrix()
func restorePerspectiveProjection
glMatrixMode(GL_PROJECTION)
// restore previous projection matrix
glPopMatrix()
// get back to modelview mode
glMatrixMode(GL_MODELVIEW)
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func setOrthographicProjection
// switch to projection mode
glMatrixMode(GL_PROJECTION)
// save previous matrix which contains the
//settings for the perspective projection
glPushMatrix()
// reset matrix
glLoadIdentity()
// set a 2D orthographic projection
gluOrtho2D(0, w, h, 0)
// switch back to modelview mode
glMatrixMode(GL_MODELVIEW)
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 9 SnowMen
for i = -3 to -1
for j = -3 to -1
glPushMatrix()
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glTranslatef(i*10.0, 0.0, j * 10.0)
drawSnowMan()
number = (i+3)*3+(j+3)
renderBitmapString(0.0, 0.5, 0.0,font ,""+number)
glPopMatrix()
next
next
// Code to compute frames per second
frame++
time=glutGet(GLUT_ELAPSED_TIME)
if time - timebase > 1000
s = "RingFreeGLUT - FPS: " + (frame*1000.0/(time-timebase))
timebase = time
frame = 0
ok
// Code to display a string (fps) with bitmap fonts
setOrthographicProjection()
glPushMatrix()
glLoadIdentity()
renderBitmapString(5,30,0,GLUT_BITMAP_HELVETICA_18,s)
glPopMatrix()
restorePerspectiveProjection()
glutSwapBuffers()
// -----------------------------------
// KEYBOARD
// -----------------------------------
func processNormalKeys
key = glutEventKey()
xx = glutEventX()
yy = glutEventY()
switch key
on 27
glutDestroyMenu(mainMenu)
glutDestroyMenu(fillMenu)
glutDestroyMenu(colorMenu)
glutDestroyMenu(fontMenu)
Shutdown()
off
func pressKey
key = glutEventKey()
xx = glutEventX()
yy = glutEventY()
switch key
on GLUT_KEY_UP
54.14. Frames Per Second 524