Delta zeta not applied by gltranslatef - c++

Question

The program should simulate a planet rotating around another planet.
I use gltranslatef to let the planet move around the bigger planet, but the problem is that the planet should hide when is over the bigger planet, because dz is -0.5.
But if I test the program I always see the red planet over the blue one.
Another problem I have: the planet rotates too fast, how do I slow it?
#include <OpenGL/OpenGL.h>
#include <GLUT/GLUT.h>
#include "utility.h"
GLfloat dx=0.0;
GLfloat dz=-0.5;
bool plus=true;
void init()
{
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glLoadIdentity();
glOrtho(-1, 1, -1, 1, -1, 1);
glEnable(GLUT_DEPTH);
}
void render()
{
glClearColor(BLACK);
glClear(GL_COLOR_BUFFER_BIT);
glColor4f(BLUE);
glutWireSphere(0.25, 100, 100);
glPushMatrix();
glLoadIdentity();
glTranslatef(-0.5+dx, 0.0, -dz);
glColor4f(RED);
glutWireSphere(0.05, 100, 100);
glPopMatrix();
glFlush();
}
void idle()
{
if(plus)
{
dx+=0.05;
}
else
{
dx-=0.05;
}
if(dx>=1.0)
{
dx=0.5;
plus=false;
}
else if(dx<=-0.0)
{
dx=0.0;
plus=true;
}
glutPostRedisplay();
}
int main(int argc, const char * argv[])
{
glutInit(&argc, (char**)argv);
glutInitWindowSize(500, 500);
glutInitWindowPosition(150, 150);
glutInitWindowPosition(0, 0);
glutCreateWindow("Simple");
glutIdleFunc(idle);
init();
glutDisplayFunc(render);
glutMainLoop();
return 0;
}
I haven't understood well how does the idle function work, why it gets called so many times? Can't I choose a time interval with which the idle function gets called?
More info: RED and BLUE are RGB floats, defined in the utility.h header file.
plus is a bool that is used to know if I have to decrease or increase dx.

Answer 1

Give this a shot:
#include <GL/glut.h>
double GetSeconds()
{
return glutGet(GLUT_ELAPSED_TIME) / 1000.0f;
}
void render()
{
glClearColor(0,0,0,0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glColor3ub(0,0,255);
glutWireSphere(0.25, 100, 100);
glPushMatrix();
glLoadIdentity();
static double prv = GetSeconds();
double cur = GetSeconds();
double delta = cur - prv;
prv = cur;
const float DEG_PER_SEC = 60.0f;
static float angle = 0.0f;
angle += DEG_PER_SEC * delta;
while( angle > 360 ) angle -= 360;
glPushMatrix();
glRotatef( angle, 0, 1, 0 );
glTranslatef( 0.5, 0, 0);
glColor3ub(255,0,0);
glutWireSphere(0.05, 100, 100);
glPopMatrix();
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-1, 1, -1, 1, -1, 1);
}
void timer(int extra)
{
glutPostRedisplay();
glutTimerFunc(16, timer, 0);
}
int main(int argc, const char * argv[])
{
glutInit(&argc, (char**)argv);
glutInitWindowSize(500, 500);
glutInitWindowPosition(150, 150);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutCreateWindow("Simple");
glutReshapeFunc(reshape);
glutTimerFunc(0, timer, 0);
glutDisplayFunc(render);
glEnable( GL_DEPTH_TEST );
glutMainLoop();
return 0;
}
Important parts:
Explicit glMatrixMode() calls
Calling glutInitDisplayMode() before glutCreateWindow()
Double-buffering requires glutSwapBuffers()
Clearing the depth buffer via GL_DEPTH_BUFFER_BIT
glEnable( GL_DEPTH_TEST )
glRotatef() for planet rotation
Timer-based animation