camera on sphere at opengl -- problem with rotation and initial window - opengl

Question

i want to make a sphere and put a camera which focuses at the center ,having a vector (VUP=0,1,0).I want to alter the spherical coordinates r,theta,phi.
The problem is that when i run the application,the sphere appears but when i press a key it disappears.
If i delete the glMatrixMode(GL_PROJECTION) from the setupmywindow,then at the beginning the sphere doesn't appear ,but if i press a key it appears.Then , bu pressing "r" and "p" ,it changes its radius but pressing "u" and "f" it rotates only one step.
#define PI 3.1415f
float theta = 0, phi = 0, dtheta = PI / 20, dphi = PI / 20;
float r = 0.2;
void setupmywindow()
{
glClearColor(1.0,1.0,1.0,0);
glColor3f(0.0, 0.0, 0.0);
glPolygonMode(GL_FRONT_AND_BACK,GL_FILL);
glMatrixMode(GL_PROJECTION);
gluPerspective(30,1,2,100);
glMatrixMode(GL_MODELVIEW);
glEnable(GL_DEPTH_TEST);
}
void myaxes(double size)
{
glBegin(GL_LINES);
glColor3f(0,0,0);glVertex3f(0,0,0); glColor3f(1,0,0);glVertex3f(size,0,0); //x-axis
glColor3f(0,0,0);glVertex3f(0,0,0); glColor3f(0,1,0);glVertex3f(0,size,0); //y-axis
glColor3f(0,0,0);glVertex3f(0,0,0); glColor3f(0,0,1);glVertex3f(0,0,size); //z-axis
glEnd();
}
void sphere()
{
float z1, x1, y1, z2, x2, y2, z3, x3, y3, z4, x4, y4;
float angle = 0,translate;
glTranslatef(0.0,0.0,translate);
angle++;
glRotatef(angle, 1.0, 1.0, 1.0);
glBegin(GL_QUAD_STRIP);
for(theta=0;theta<=2.0*PI;theta+=dtheta)
{
for(phi=0;phi<=PI;phi+=dphi)
{
z1 = r * sin(phi + dphi) * cos(theta + dtheta);
x1 = r * sin(phi + dphi) * sin(theta + dtheta);
y1 = r * cos(phi + dphi);
z2 = r * sin(phi) * cos(theta + dtheta);
x2 = r * sin(phi) * sin(theta + dtheta);
y2 = r * cos(phi);
z3 = r * sin(phi) * cos(theta);
x3 = r * sin(phi) * sin(theta);
y3 = r * cos(phi);
z4 = r * sin(phi + dphi) * cos(theta);
x4 = r * sin(phi + dphi) * sin(theta);
y4 = r * cos(phi + dphi);
glColor3f(1,0,0);
glVertex3f(x4, y4, z4);
glVertex3f(x1, y1, z1);
glVertex3f(x2, y2, z2);
glVertex3f(x3, y3, z3);
}
}
glEnd();
}
void myDrawing()
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(r,theta,phi,0,0,0,0,1,0);
sphere();
myaxes(1.5);
glutSwapBuffers();
}
void mykeyboardcontrol(unsigned char key, int x, int y)
{
switch(key){
case 'r': r+=0.1;break; //increase radius
case 'p': r-=0.1;break; //decrease radius
case 'u': theta+=PI/20;break;//increase theta angle
case 'f': phi+=PI/20;break;//increase phi angle
}
printf("r=%f theta=%f phi=%f\n",r,theta,phi);
if(key==27) exit(0);
if(theta>2*PI) theta-=2*PI;
if(phi>PI) phi-=PI;
printf("r=%f theta=%f phi=%f\n",r,theta,phi);
glutPostRedisplay();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);
glutCreateWindow("Sphere");
setupmywindow();
glutDisplayFunc(myDrawing);
glutKeyboardFunc(mykeyboardcontrol);
glutMainLoop();
}

Answer 1

Here you go:
#include <GL/glut.h>
#include <cmath>
#include <cstdlib>
#include <cstdio>
const float PI = 3.14159f;
float camera_theta = 2.042033;
float camera_phi = 8.639376;
float camera_r = 15;
double aspect_ratio = 0;
void reshape(int w, int h)
{
aspect_ratio = (double)w / (double)h;
glViewport(0, 0, w, h);
}
void setupmywindow()
{
glClearColor(1,1,1,0);
glPolygonMode(GL_FRONT_AND_BACK,GL_FILL);
}
void myaxes(double size)
{
glBegin(GL_LINES);
glColor3f(0,0,0);
glVertex3f(0,0,0);
glColor3f(1,0,0);
glVertex3f(size,0,0); //x-axis
glColor3f(0,0,0);
glVertex3f(0,0,0);
glColor3f(0,1,0);
glVertex3f(0,size,0); //y-axis
glColor3f(0,0,0);
glVertex3f(0,0,0);
glColor3f(0,0,1);
glVertex3f(0,0,size); //z-axis
glEnd();
}
void sphere(float radius)
{
float z1, x1, y1, z2, x2, y2, z3, x3, y3, z4, x4, y4;
float dtheta = PI / 20;
float dphi = PI / 20;
glBegin(GL_QUADS);
for( float theta = 0; theta<=2.0*PI; theta+=dtheta )
{
for( float phi = 0; phi<=PI; phi+=dphi )
{
z1 = radius * sin(phi + dphi) * cos(theta + dtheta);
x1 = radius * sin(phi + dphi) * sin(theta + dtheta);
y1 = radius * cos(phi + dphi);
z2 = radius * sin(phi) * cos(theta + dtheta);
x2 = radius * sin(phi) * sin(theta + dtheta);
y2 = radius * cos(phi);
z3 = radius * sin(phi) * cos(theta);
x3 = radius * sin(phi) * sin(theta);
y3 = radius * cos(phi);
z4 = radius * sin(phi + dphi) * cos(theta);
x4 = radius * sin(phi + dphi) * sin(theta);
y4 = radius * cos(phi + dphi);
glColor3f(1,0,0);
glVertex3f(x4, y4, z4);
glVertex3f(x1, y1, z1);
glVertex3f(x2, y2, z2);
glVertex3f(x3, y3, z3);
}
}
glEnd();
}
void display(void)
{
glEnable(GL_DEPTH_TEST);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45, aspect_ratio, 1, 100);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
// spherical coordinate camera transform, +Z is "up"
glTranslatef(0 ,0 , -camera_r);
glRotatef( (camera_theta - PI) * (180.0f/PI), 1,0,0 );
glRotatef( -camera_phi * (180.0f/PI), 0,0,1 );
sphere(2);
myaxes(5);
glutSwapBuffers();
}
void mykeyboardcontrol(unsigned char key, int x, int y)
{
switch(key){
case 'r': camera_r+=0.1;break; //increase radius
case 'p': camera_r-=0.1;break; //decrease radius
case 'i': camera_theta+=PI/20;break;//increase theta angle
case 'k': camera_theta-=PI/20;break;//increase theta angle
case 'j': camera_phi-=PI/20;break;//increase phi angle
case 'l': camera_phi+=PI/20;break;//increase phi angle
}
printf("r=%f theta=%f phi=%f\n",camera_r,camera_theta,camera_phi);
if(key==27) exit(0);
// clamp theta
if( camera_theta < 0 ) camera_theta = 0;
if( camera_theta > PI ) camera_theta = PI;
// wrap phi
if( camera_phi > 2*PI ) camera_phi -= 2*PI;
if( camera_phi < 2*PI ) camera_phi += 2*PI;
printf("r=%f theta=%f phi=%f\n",camera_r,camera_theta,camera_phi);
glutPostRedisplay();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);
glutInitWindowSize(400,400);
glutCreateWindow("Sphere");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(mykeyboardcontrol);
setupmywindow();
glutMainLoop();
return 0;
}
I have no clue why you were trying to pass r, theta, and phi into gluLookAt(), so I replaced that with a fixed oblique-ish camera angle looking at the origin. Also you seem to be overwriting theta and phi in sphere(), blasting away whatever mykeyboardcontrol() is trying to do. I couldn't tell if you want to orbit the camera around the origin or draw a partial sphere.