OpenGl display animation and draw text - c++

Question

I want to display the solar system and draw a simple text saying " Hello world " :
This code below display the solar system and everything works:
#include <iostream>
#include <OpenGL/gl.h>
#include <GLUT/glut.h>
void OpenGLInit(void);
static void Animate(void );
static void Key_r(void );
static void Key_s(void );
static void Key_up(void );
static void Key_down(void );
static void ResizeWindow(int w, int h);
static void KeyPressFunc( unsigned char Key, int x, int y );
static void SpecialKeyFunc( int Key, int x, int y );
static GLenum spinMode = GL_TRUE;
static GLenum singleStep = GL_FALSE;
// These three variables control the animation's state and speed.
static float HourOfDay = 0.0;
static float DayOfYear = 0.0;
static float AnimateIncrement = 24.0; // Time step for animation (hours)
// glutKeyboardFunc is called below to set this function to handle
// all normal key presses.
static void KeyPressFunc( unsigned char Key, int x, int y )
{
switch ( Key ) {
case 'R':
case 'r':
Key_r();
break;
case 's':
case 'S':
Key_s();
break;
case 27: // Escape key
exit(1);
}
}
// glutSpecialFunc is called below to set this function to handle
// all special key presses. See glut.h for the names of
// special keys.
static void SpecialKeyFunc( int Key, int x, int y )
{
switch ( Key ) {
case GLUT_KEY_UP:
Key_up();
break;
case GLUT_KEY_DOWN:
Key_down();
break;
}
}
static void Key_r(void)
{
if ( singleStep ) { // If ending single step mode
singleStep = GL_FALSE;
spinMode = GL_TRUE; // Restart animation
}
else {
spinMode = !spinMode; // Toggle animation on and off.
}
}
static void Key_s(void)
{
singleStep = GL_TRUE;
spinMode = GL_TRUE;
}
static void Key_up(void)
{
AnimateIncrement *= 2.0; // Double the animation time step
}
static void Key_down(void)
{
AnimateIncrement /= 2.0; // Halve the animation time step
}
/*
* Animate() handles the animation and the redrawing of the
* graphics window contents.
*/
static void Animate(void)
{
// Clear the redering window
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
if (spinMode) {
// Update the animation state
HourOfDay += AnimateIncrement;
DayOfYear += AnimateIncrement/24.0;
HourOfDay = HourOfDay - ((int)(HourOfDay/24))*24;
DayOfYear = DayOfYear - ((int)(DayOfYear/365))*365;
}
// Clear the current matrix (Modelview)
glLoadIdentity();
// Back off eight units to be able to view from the origin.
glTranslatef ( 0.0, 0.0, -8.0 );
// Rotate the plane of the elliptic
// (rotate the model's plane about the x axis by fifteen degrees)
glRotatef( 15.0, 1.0, 0.0, 0.0 );
// Draw the sun -- as a yellow, wireframe sphere
glColor3f( 1.0, 1.0, 0.0 );
glutWireSphere( 1.0, 15, 15 );
// Draw the Earth
// First position it around the sun
// Use DayOfYear to determine its position
glRotatef( 360.0*DayOfYear/365.0, 0.0, 1.0, 0.0 );
glTranslatef( 4.0, 0.0, 0.0 );
glPushMatrix(); // Save matrix state
// Second, rotate the earth on its axis.
// Use HourOfDay to determine its rotation.
glRotatef( 360.0*HourOfDay/24.0, 0.0, 1.0, 0.0 );
// Third, draw the earth as a wireframe sphere.
glColor3f( 0.2, 0.2, 1.0 );
glutWireSphere( 0.4, 10, 10);
glPopMatrix(); // Restore matrix state
// Draw the moon.
// Use DayOfYear to control its rotation around the earth
glRotatef( 360.0*12.0*DayOfYear/365.0, 0.0, 1.0, 0.0 );
glTranslatef( 0.7, 0.0, 0.0 );
glColor3f( 0.3, 0.7, 0.3 );
glutWireSphere( 0.1, 5, 5 );
// Flush the pipeline, and swap the buffers
glFlush();
glutSwapBuffers();
if ( singleStep ) {
spinMode = GL_FALSE;
}
glutPostRedisplay(); // Request a re-draw for animation purposes
}
// Initialize OpenGL's rendering modes
void OpenGLInit(void)
{
glShadeModel( GL_FLAT );
glClearColor( 0.0, 0.0, 0.0, 0.0 );
glClearDepth( 1.0 );
glEnable( GL_DEPTH_TEST );
}
// ResizeWindow is called when the window is resized
static void ResizeWindow(int w, int h)
{
float aspectRatio;
h = (h == 0) ? 1 : h;
w = (w == 0) ? 1 : w;
glViewport( 0, 0, w, h ); // View port uses whole window
aspectRatio = (float)w/(float)h;
// Set up the projection view matrix (not very well!)
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective( 60.0, aspectRatio, 1.0, 30.0 );
// Select the Modelview matrix
glMatrixMode( GL_MODELVIEW );
}
// Main routine
// Set up OpenGL, hook up callbacks, and start the main loop
int main( int argc, char** argv )
{
// Need to double buffer for animation
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
// Create and position the graphics window
glutInitWindowPosition( 0, 0 );
glutInitWindowSize( 600, 360 );
glutCreateWindow( "Solar System Demo" );
// Initialize OpenGL.
OpenGLInit();
// Set up callback functions for key presses
glutKeyboardFunc( KeyPressFunc );
glutSpecialFunc( SpecialKeyFunc );
// Set up the callback function for resizing windows
glutReshapeFunc( ResizeWindow );
// Callback for graphics image redrawing
glutDisplayFunc( Animate );
// Start the main loop. glutMainLoop never returns.
glutMainLoop( );
return(0); // Compiler requires this to be here. (Never reached)
}
The code below draw text " Hello world " and works too:
#include <iostream>
#include <OpenGL/gl.h>
#include <GLUT/glut.h>
void drawBitmapText(char *string,float x,float y,float z)
{
char *c;
glRasterPos3f(x, y,z);
for (c=string; *c != '\0'; c++)
{
glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_10, *c);
}
}
void drawStrokeText(char*string,int x,int y,int z)
{
char *c;
glPushMatrix();
glTranslatef(x, y+8,z);
// glScalef(0.09f,-0.08f,z);
for (c=string; *c != '\0'; c++)
{
glutStrokeCharacter(GLUT_STROKE_ROMAN , *c);
}
glPopMatrix();
}
void reshape(int w,int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0,w,h,0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
void render(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glColor3f(0,1,0);
drawBitmapText("Hello world",200,200,0);
glutSwapBuffers();
}
// Main routine
// Set up OpenGL, hook up callbacks, and start the main loop
int main( int argc, char** argv )
{
// Need to double buffer for animation
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
// Create and position the graphics window
glutInitWindowPosition( 0, 0 );
glutInitWindowSize( 600, 360 );
glutCreateWindow( "Solar System Demo" );
glutDisplayFunc(render);
glutIdleFunc(render);
glutReshapeFunc(reshape);
// Start the main loop. glutMainLoop never returns.
glutMainLoop( );
return(0); // Compiler requires this to be here. (Never reached)
}
i'm trying to use both of them together to display the solar system and draw the text, but
i'm getting a blank, black screen:
#include <iostream>
#include <OpenGL/gl.h>
#include <GLUT/glut.h>
void OpenGLInit(void);
static void Animate(void );
static void Key_r(void );
static void Key_s(void );
static void Key_up(void );
static void Key_down(void );
static void ResizeWindow(int w, int h);
static void KeyPressFunc( unsigned char Key, int x, int y );
static void SpecialKeyFunc( int Key, int x, int y );
static GLenum spinMode = GL_TRUE;
static GLenum singleStep = GL_FALSE;
// These three variables control the animation's state and speed.
static float HourOfDay = 0.0;
static float DayOfYear = 0.0;
static float AnimateIncrement = 24.0; // Time step for animation (hours)
// glutKeyboardFunc is called below to set this function to handle
// all normal key presses.
static void KeyPressFunc( unsigned char Key, int x, int y )
{
switch ( Key ) {
case 'R':
case 'r':
Key_r();
break;
case 's':
case 'S':
Key_s();
break;
case 27: // Escape key
exit(1);
}
}
// glutSpecialFunc is called below to set this function to handle
// all special key presses. See glut.h for the names of
// special keys.
static void SpecialKeyFunc( int Key, int x, int y )
{
switch ( Key ) {
case GLUT_KEY_UP:
Key_up();
break;
case GLUT_KEY_DOWN:
Key_down();
break;
}
}
static void Key_r(void)
{
if ( singleStep ) { // If ending single step mode
singleStep = GL_FALSE;
spinMode = GL_TRUE; // Restart animation
}
else {
spinMode = !spinMode; // Toggle animation on and off.
}
}
static void Key_s(void)
{
singleStep = GL_TRUE;
spinMode = GL_TRUE;
}
static void Key_up(void)
{
AnimateIncrement *= 2.0; // Double the animation time step
}
static void Key_down(void)
{
AnimateIncrement /= 2.0; // Halve the animation time step
}
/*
* Animate() handles the animation and the redrawing of the
* graphics window contents.
*/
static void Animate(void)
{
// Clear the redering window
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
if (spinMode) {
// Update the animation state
HourOfDay += AnimateIncrement;
DayOfYear += AnimateIncrement/24.0;
HourOfDay = HourOfDay - ((int)(HourOfDay/24))*24;
DayOfYear = DayOfYear - ((int)(DayOfYear/365))*365;
}
// Clear the current matrix (Modelview)
glLoadIdentity();
// Back off eight units to be able to view from the origin.
glTranslatef ( 0.0, 0.0, -8.0 );
// Rotate the plane of the elliptic
// (rotate the model's plane about the x axis by fifteen degrees)
glRotatef( 15.0, 1.0, 0.0, 0.0 );
// Draw the sun -- as a yellow, wireframe sphere
glColor3f( 1.0, 1.0, 0.0 );
glutWireSphere( 1.0, 15, 15 );
// Draw the Earth
// First position it around the sun
// Use DayOfYear to determine its position
glRotatef( 360.0*DayOfYear/365.0, 0.0, 1.0, 0.0 );
glTranslatef( 4.0, 0.0, 0.0 );
glPushMatrix(); // Save matrix state
// Second, rotate the earth on its axis.
// Use HourOfDay to determine its rotation.
glRotatef( 360.0*HourOfDay/24.0, 0.0, 1.0, 0.0 );
// Third, draw the earth as a wireframe sphere.
glColor3f( 0.2, 0.2, 1.0 );
glutWireSphere( 0.4, 10, 10);
glPopMatrix(); // Restore matrix state
// Draw the moon.
// Use DayOfYear to control its rotation around the earth
glRotatef( 360.0*12.0*DayOfYear/365.0, 0.0, 1.0, 0.0 );
glTranslatef( 0.7, 0.0, 0.0 );
glColor3f( 0.3, 0.7, 0.3 );
glutWireSphere( 0.1, 5, 5 );
// Flush the pipeline, and swap the buffers
glFlush();
glutSwapBuffers();
if ( singleStep ) {
spinMode = GL_FALSE;
}
glutPostRedisplay(); // Request a re-draw for animation purposes
}
// Initialize OpenGL's rendering modes
void OpenGLInit(void)
{
glShadeModel( GL_FLAT );
glClearColor( 0.0, 0.0, 0.0, 0.0 );
glClearDepth( 1.0 );
glEnable( GL_DEPTH_TEST );
}
// ResizeWindow is called when the window is resized
static void ResizeWindow(int w, int h)
{
float aspectRatio;
h = (h == 0) ? 1 : h;
w = (w == 0) ? 1 : w;
glViewport( 0, 0, w, h ); // View port uses whole window
aspectRatio = (float)w/(float)h;
// Set up the projection view matrix (not very well!)
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective( 60.0, aspectRatio, 1.0, 30.0 );
// Select the Modelview matrix
glMatrixMode( GL_MODELVIEW );
}
void drawBitmapText(char *string,float x,float y,float z)
{
char *c;
glRasterPos3f(x, y,z);
for (c=string; *c != '\0'; c++)
{
glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_10, *c);
}
}
void drawStrokeText(char*string,int x,int y,int z)
{
char *c;
glPushMatrix();
glTranslatef(x, y+8,z);
// glScalef(0.09f,-0.08f,z);
for (c=string; *c != '\0'; c++)
{
glutStrokeCharacter(GLUT_STROKE_ROMAN , *c);
}
glPopMatrix();
}
void reshape(int w,int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0,w,h,0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
void render(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glColor3f(0,1,0);
drawBitmapText("Hello world",200,200,0);
glutSwapBuffers();
}
// Main routine
// Set up OpenGL, hook up callbacks, and start the main loop
int main( int argc, char** argv )
{
// Need to double buffer for animation
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
// Create and position the graphics window
glutInitWindowPosition( 0, 0 );
glutInitWindowSize( 600, 360 );
glutCreateWindow( "Solar System Demo" );
// Initialize OpenGL.
OpenGLInit();
// Set up callback functions for key presses
glutKeyboardFunc( KeyPressFunc );
glutSpecialFunc( SpecialKeyFunc );
// Set up the callback function for resizing windows
glutReshapeFunc( ResizeWindow );
// Callback for graphics image redrawing
glutDisplayFunc( Animate );
glutDisplayFunc(render);
glutIdleFunc(render);
glutReshapeFunc(reshape);
// Start the main loop. glutMainLoop never returns.
glutMainLoop( );
return(0); // Compiler requires this to be here. (Never reached)
}

Answer 1

These lines in main() cause the problem:
glutKeyboardFunc( KeyPressFunc );
glutSpecialFunc( SpecialKeyFunc );
glutReshapeFunc( ResizeWindow );
glutDisplayFunc( Animate );
glutDisplayFunc(render);
glutIdleFunc(render);
The glutDisplayFunc() overwrites the internal function pointer inside the GLUT. So only the render() function gets called, not the Animate().
The second problem here: Idle function is also the render(), so it gets called twice. The same with Reshape function.
You need to combine the ResizeWindow() and reshape() functions, then render() and Animate() function and then remove the glutIdleFunc call since iteverything is done in the render() already.