openGL fixing camera? - c++

Question

This code makes cube. Code works correctly.
But, if I increase the vertex values, it does not show in the display. I want bigger cube, but bigger cube does not show in display. How can I fix it??
Thanks for answers...
#define A glVertex3f (-0.5, 0.5, -0.5)
#define B glVertex3f (-0.5, -0.5, -0.5)
#define C glVertex3f ( 0.5, -0.5, -0.5)
#define D glVertex3f ( 0.5, 0.5, -0.5)
#define E glVertex3f (-0.5, 0.5, 0.5)
#define F glVertex3f (-0.5, -0.5, 0.5)
#define G glVertex3f ( 0.5, -0.5, 0.5)
#define H glVertex3f ( 0.5, 0.5, 0.5)
#define _USE_MATH_DEFINES
#include <cmath>
#include <stdlib.h>
#include <math.h>
#include <glut.h>
float distance = 5.0;
int longitude = 0, latitude = 0, ainc = 5;
int lastx = -1, lasty = -1;
void display (void)
{
float xc, yc, zc;
int type = GL_POLYGON; // or GL_LINE_LOOP
xc = distance * cos (latitude /180.0*M_PI) * cos (longitude/180.0*M_PI);
yc = distance * sin (latitude /180.0*M_PI);
zc = distance * cos (latitude /180.0*M_PI) * sin (longitude/180.0*M_PI);
glLoadIdentity ();
gluLookAt (xc, yc, zc, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Sides of the cube as loops or polygons, in anti-clockwise order.
glColor3f (1.0, 0.0, 0.0);
glBegin (type); A; B; C; D; glEnd(); // front
glColor3f (0.0, 1.0, 0.0);
glBegin (type); H; E; F; G; glEnd(); // back
glColor3f (0.0, 0.0, 1.0);
glBegin (type); B; C; G; F; glEnd(); // bottom
glColor3f (1.0, 0.0, 1.0);
glBegin (type); A; D; H; E; glEnd(); // top
glColor3f (0.0, 1.0, 1.0);
glBegin (type); A; E; F; B; glEnd(); // left
glColor3f (1.0, 1.0, 0.0);
glBegin (type); D; C; G; H; glEnd(); // right
glutSwapBuffers ();
}
void keyboard (unsigned char key, int x, int y)
{
switch (key) {
case 27: case 'q': case 'Q':
exit (EXIT_SUCCESS);
break;
}
}
void special (int key, int x, int y)
{
switch (key) {
case GLUT_KEY_UP:
distance *= 1.1;
break;
case GLUT_KEY_DOWN:
distance /= 1.1;
break;
}
glutPostRedisplay ();
}
void click (int button, int state, int x, int y)
{
if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
lastx = x;
lasty = y;
}
}
void mouse (int x, int y)
{
if (x > lastx) {
longitude = (longitude + ainc) % 360;
} else if (x < lastx) {
longitude = (longitude - ainc) % 360;
}
if (y > lasty) {
latitude = (latitude + ainc) % 360;
} else if (y < lasty) {
latitude = (latitude - ainc) % 360;
}
lastx = x;
lasty = y;
glutPostRedisplay ();
}
void reshape (int w, int h)
{
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
gluPerspective (65.0, (GLfloat) w / (GLfloat) h, 1.0, 20.0);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
glTranslatef (0.0, 0.0, -5.0);
}
int main (int argc, char *argv[])
{
glutInit (&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutCreateWindow (argv[0]);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
gluPerspective(50.0, 1.0, 3.0, 7.0);
glMatrixMode (GL_MODELVIEW);
glutDisplayFunc (display);
glutKeyboardFunc (keyboard);
glutSpecialFunc (special);
glutMouseFunc (click);
glutMotionFunc (mouse);
glutReshapeFunc (reshape);
glEnable (GL_DEPTH_TEST);
glutMainLoop ();
return EXIT_SUCCESS;
}

Answer 1

I suspect it's you perspective that's broken.
Your near and far planes are 3.0 and 7.0 units. If you move your points outside these planes they will be removed. You also use 1.0 and 20.0 when you reshape the window, but they won't be used unless there's a reshape event.
I don't know what values you use for your cube but I think you move outside of your defined range. Try increasing the difference between the near and far places and make sure your cube falls between them.
For more info on gluPerspective see the documentation.

Answer 2

To scale an object's vertices, you only have to multiply them by the same number. For example if you want to make a cube twice as large, multiply all vertices by 2.0.
If the cube becomes so large that it's front side goes behind the "camera" then it will not render, and if your settings do not render the "back side" of faces, then your cube will not render at all (because the camera will be inside it).
You can also use glScalef(float x, float y, float z)