Question

I’m learning OpenGL; I managed to make my first 2D program but I am stuck on using gluPerspective.

I’m trying a little test to try to grasp how I can go about making a 3D project but I can’t seem to figure out what I am missing and what is needed to make this small test work:

void init_perspective()

{

SDL_Init(SDL_INIT_EVERYTHING); 
SDL_SetVideoMode(640, 480, 32, SDL_OPENGL); 
SDL_WM_SetCaption( "OpenGL Test", NULL ); 

glClearColor( 0, 0, 0, 0 ); 
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective(45, 1.333, 0, 100); 
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glClear( GL_COLOR_BUFFER_BIT );

}

int main( int argc, char **argv)

{

init_perspective();

glTranslatef( 200, 200, 50 );
glColor4f(1.0,1.0,1.0,1.0);

glBegin(GL_QUADS);

    glVertex3f(0, 0 ,0);
    glVertex3f(50,0 ,10);
    glVertex3f(50,50,30);
    glVertex3f(0, 50,0);

glEnd();

glLoadIdentity();

SDL_GL_SwapBuffers();

SDL_Delay(1000);

SDL_Quit();

return 0;

}

If anybody could tell me what function calls I could use and are missing in this test code so I could have a play around and learn how 3D OpenGL works I would be grateful.

Answer 1

gluPerspective(45, 1.333, 0, 100);

Never set zNear to zero. It messes up the math:

Because r = zFar / zNear approaches infinity as zNear approaches 0, zNear must never be set to 0.

Choose some small positive number like 0.01 or 12.

EDIT: Also, put your camera somewhere such that it can see your geometry:

int main( int argc, char **argv)
{
init_perspective();

glTranslatef(0,0,-5);
glColor4f(1.0,1.0,1.0,1.0);

glBegin(GL_QUADS);
    glVertex2f(-1,-1);
    glVertex2f( 1,-1);
    glVertex2f( 1, 1);
    glVertex2f(-1, 1);
glEnd();

SDL_GL_SwapBuffers();

SDL_Delay(1000);

SDL_Quit();

return 0;
}

By default it’s looking down the -Z axis from position (0,0,0).