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In my last post I mentioned I was having issue with remembering the order to draw vertices for quads. Ha… the light came on tonight while I was working on the various tutorials I’ve come across. The bottom and back faces of a cube I am actually drawing the quad from the perspective of viewing the back face. Apparently when drawing a quad (or triangle for that matter) you draw the vertices in counter-clockwise order to draw the FRONT face as the side facing the observer, or you draw the vertices clockwise to draw the BACK face as the side facing the observer. Boy, once I got that, it sure seemed a lot easier!
As an example of drawing a basic cube, colored all pretty and green.
glBegin(GL_QUADS);
// Front face
glNormal3f(0.0f, 0.0f, 1.0f);
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(-1.2f, -0.5f, 0.5f);
glVertex3f(1.2f, -0.5f, 0.5f);
glVertex3f(1.2f, 0.5f, 0.5f);
glVertex3f(-1.2f, 0.5f, 0.5f);
// Back face
glNormal3f(0.0f, 0.0f, -1.0f);
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(-1.2f, -0.5f, -0.5f);
glVertex3f(-1.2f, 0.5f, -0.5f);
glVertex3f(1.2f, 0.5f, -0.5f);
glVertex3f(1.2f, -0.5f, -0.5f);
// Top face
glNormal3f(0.0f, 1.0f, 0.0f);
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(-1.2f, 0.5f, -0.5f);
glVertex3f(-1.2f, 0.5f, 0.5f);
glVertex3f(1.2f, 0.5f, 0.5f);
glVertex3f(1.2f, 0.5f, -0.5f);
// Bottom face
glNormal3f(0.0f, -1.0f, 0.0f);
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(-1.2f, -0.5f, -0.5f);
glVertex3f(1.2f, -0.5f, -0.5f);
glVertex3f(1.2f, -0.5f, 0.5f);
glVertex3f(-1.2f, -0.5f, 0.5f);
// Right face
glNormal3f(1.0f, 0.0f, 0.0f);
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(1.2f, -0.5f, -0.5f);
glVertex3f(1.2f, -0.5f, 0.5f);
glVertex3f(1.2f, 0.5f, 0.5f);
glVertex3f(1.2f, 0.5f, -0.5f);
// Left face
glNormal3f(-1.0f, 0.0f, 0.0f);
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(-1.2f, -0.5f, -0.5f);
glVertex3f(-1.2f, -0.5f, 0.5f);
glVertex3f(-1.2f, 0.5f, 0.5f);
glVertex3f(-1.2f, 0.5f, -0.5f);
glEnd();