Greetings,

While working with NeHe #33 tutorial, I tried setting glMatrixMode(GL_PROJECTION) with some standard resolutions, (0, 800, 0, 600), etc.
However, when I invoke this call in the init portion of the code, the rotating sprites disappear. I have no idea how what the coordinates correspond to, when rendering the GL_QUADS.

Would anyone be able to show me how to set this up whilst having the glMatrixMode set to GL_PROJECTION?

I do something like this:


void SetPerspective(float fov, float aspect, float znear, float zfar)
{
float top, bottom, left, right;

top = znear * tan(fov / 2 * DEG2RAD);
bottom = -top;
right = aspect * top;
left = -right;

glFrustum(left, right, bottom, top, znear, zfar);
}


void Draw_Perspective()
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
SetPerspective(camera_fov, (float)(app_rect.right - app_rect.left)/(app_rect.bottom - app_rect.top), 1, 99999);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glRotatef(camera_angles.x, 1, 0, 0);
glRotatef(camera_angles.y, 0, 1, 0);
glRotatef(camera_angles.z, 0, 0, 1);
glTranslatef(-camera_origin.x, -camera_origin.y, -camera_origin.z);
}

void Draw_Ortho()
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, VID_WIDTH, VID_HEIGHT, 0, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}




The glOrtho takes arguments (left-side, right-side, bottom, top, near, far) it looks like you had it backwards, but that's ok, the OpenGL guys got it backwards IMHO

Oh and to minimize linkage I use glOrtho and glFrustum instead of any glu stuff so that I'm not linking more than is really necessary, but it's really no biggie.