Opengl viewpoint transformation how to gluLookAt - c

Question

I would like to use the polar coordinates to manipulate the upper, lower, left, and right camera points with my keyboard.
#include <stdlib.h>
#include <glut.h>
GLint TopLeftX, TopLeftY, BottomRightX, BottomRightY ;
static int HourOfDay = 0;
static int DayOfYear = 10;
void init(void) {
glClearColor(0.0, 0.0, 0.0, 0.0);
}
void myDisplay(void) {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glPushMatrix(); // Origin
glClear(GL_DEPTH_BUFFER_BIT);
/* Sun */
glColor3f(1.0, 1.0, 0.0);
glutSolidSphere(1.0, 20, 10);
/* Mercury */
glPushMatrix();
glRotatef((GLfloat)DayOfYear, 0.0, 0.0, 1.0);
glTranslatef(3.0, 0.0, 0.0);
glRotatef((GLfloat)HourOfDay, 0.0, 0.0, 1.0);
glColor3f(0.87, 0.53, 0.25);
glutSolidSphere(0.3, 10, 2);
glPopMatrix();
/* Venus */
glPushMatrix();
glRotatef((GLfloat)DayOfYear + 195, 0.0, 0.0, 1.0);
glTranslatef(5.0, 0.0, 0.0);
glRotatef((GLfloat)HourOfDay, 0.0, 0.0, 1.0);
glColor3f(0.99, 0.91, 0.66);
glutSolidSphere(0.5, 10, 2);
glPopMatrix();
/* Earth */
glPushMatrix();
glRotatef((GLfloat)DayOfYear + 80, 0.0, 0.0, 1.0);
glTranslatef(7.0, 0.0, 0.0);
glRotatef((GLfloat)HourOfDay, 0.0, 0.0, 1.0);
glColor3f(0.47, 0.82, 0.98);
glutSolidSphere(0.5, 10, 2);
/* Earth's Moon 1*/
glPushMatrix();
glRotatef((GLfloat)DayOfYear, 0.0, 0.0, 1.0);
glTranslatef(0.7, 0.0, 0.0);
glColor3f(0.89, 0.93, 0.95);
glutSolidSphere(0.1, 5, 5);
glPopMatrix();
glPopMatrix();
/* Mars */
glPushMatrix();
glRotatef((GLfloat)DayOfYear + 275, 0.0, 0.0, 1.0);
glTranslatef(9.0, 0.0, 0.0);
glRotatef((GLfloat)HourOfDay, 0.0, 0.0, 1.0);
glColor3f(0.84, 0.16, 0.15);
glutSolidSphere(0.35, 10, 2);
glPopMatrix();
/* Jupiter */
glPushMatrix();
glRotatef((GLfloat)DayOfYear + 33, 0.0, 0.0, 1.0);
glTranslatef(11.0, 0.0, 0.0);
glRotatef((GLfloat)HourOfDay, 0.0, 0.0, 1.0);
glColor3f(0.93, 0.64, 0.27);
glutSolidSphere(1.0, 10, 2);
glPopMatrix();
/* Saturn */
glPushMatrix();
glRotatef((GLfloat)DayOfYear + 180, 0.0, 0.0, 1.0);
glTranslatef(15.0, 0.0, 0.0);
glRotatef((GLfloat)HourOfDay, 0.0, 0.0, 1.0);
glColor3f(0.92, 0.82, 0.45);
glutSolidSphere(0.9, 10, 2);
glPopMatrix();
/* Uranus */
glPushMatrix();
glRotatef((GLfloat)DayOfYear + 90, 0.0, 0.0, 1.0);
glTranslatef(17.0, 0.0, 0.0);
glRotatef((GLfloat)HourOfDay, 0.0, 0.0, 1.0);
glColor3f(0.64, 0.84, 0.78);
glutSolidSphere(0.8, 10, 2);
glPopMatrix();
/* Neptune */
glPushMatrix();
glRotatef((GLfloat)DayOfYear + 150, 0.0, 0.0, 1.0);
glTranslatef(20.0, 0.0, 0.0);
glRotatef((GLfloat)HourOfDay, 0.0, 0.0, 1.0);
glColor3f(0.29, 0.74, 0.95);
glutSolidSphere(0.25, 10, 2);
glPopMatrix();
glutSwapBuffers();
// Animation State
DayOfYear = (DayOfYear + 1) % 360;
HourOfDay = (HourOfDay + 5) % 360;
}
void Timer(int iUnused) {
glutPostRedisplay();
glutTimerFunc(30, Timer, 0);
}
static float cam_axis_x = 0.0;
static float cam_axis_y = 0.0;
static float cam_axis_z = -50.0;
void reshape(int w, int h) {
glViewport(0, 0, (GLsizei)w, (GLsizei)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, (GLfloat)w / (GLfloat)h, 1.0, 90.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(cam_axis_x, cam_axis_y, cam_axis_z);
}
/*void reshape(int w, int h) {
glViewport(0, 0, (GLsizei)w, (GLsizei)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, (GLsizei)w / (GLsizei)h, 0.0, 90.0);
}*/
void keyboard(unsigned char key, int x, int y) {
switch (key) {
case 'q': // Esc
exit(0);
break;
case '75': // left
break;
case '77': // right
break;
case '72': // up
break;
case '80': // down
break;
}
}
void MyMouseClick(GLint Button, GLint State, GLint X, GLint Y) {
if (Button == GLUT_LEFT_BUTTON && State == GLUT_DOWN) {
TopLeftX = X;
TopLeftY = Y;
}
}
void MyMouseMove(GLint X, GLint Y) {
BottomRightX = X;
BottomRightY = Y;
glutPostRedisplay();
}
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(500, 500);
glutInitWindowPosition(100, 100);
glutCreateWindow(argv[0]);
init();
glutDisplayFunc(myDisplay);
glutReshapeFunc(reshape);
Timer(0);
glutKeyboardFunc(keyboard);
glutMouseFunc(MyMouseClick);
glutMotionFunc(MyMouseMove);
glutMainLoop();
return 0;
}
I want to move the camera around the sun
Can you tell me about gluLookAt?

Answer 1

I don't know what you mean by polar coordinates, normally it's for 2D. maybe you mean Spherical coordinates.
The method would be quite identical:
Assuming your sun is at the origin of the world (which it currently does)
You have 2 methods
Assuming Theta is the angle you want your camera to orbit around the sun
and Phi is some "pitching" around your xAxis frame (you may or may not want it).
1) Compute the x,y,z position of your camera using the basic formula:
https://en.wikipedia.org/wiki/Spherical_coordinate_system
Spherical Coordinates:
// r is the distance to the sun
cam_axis_x = r * sin(theta) * cos(phi);
cam_axis_y = r * r * cos(theta);
cam_axis_z = r * sin(theta) * sin(phi);
"Polar coordinates":
cam_axis_x = r * sin(theta);
cam_axis_z = r * cos(theta);
then apply the translation as you did before
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(cam_axis_x, cam_axis_y, cam_axis_z);
2) Apply a rotation on your camera after translating it to its original position:
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(cam_axis_x, cam_axis_y, cam_axis_z);
glRotatef(0, theta, phi);