Opengl question

Before I begin I apologize if I put this in the wrong place. But I'm pretty sure that this is the right place.

Anyways I'm just starting to learn OpenGl and I was wondering about this code.

Code:

glTranslatef(0.0f,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0 glBegin(GL_TRIANGLES); // Drawing Using Triangles glColor3f(1.0f,0.0f,0.0f); // Set The Color To Red glVertex3f( 0.0f, 1.0f, -10.0f); // Top glVertex3f(-1.0f,-1.0f, -10.0f); // Bottom Left glVertex3f( 1.0f,-1.0f, -10.0f); // Bottom Right glColor3f(0.0f,1.0f,0.0f); // Set The Color To green glVertex3f( 0.0f, 1.0f, -10.0f); // Top glVertex3f(-1.0f,-1.0f, -10.0f); // Bottom Left glVertex3f( 1.0f,-1.0f, -10.0f); // Bottom Right glEnd(); // Finished Drawing The Triangle

Anyways if I understand glTranslate correctly then thats basically the starting point for any drawing you decide to do? So the second part of the code should just cover up the first?

Thanks for reading this

Quote:

Originally Posted by Shadowwoelf

Anyways if I understand glTranslate correctly then thats basically the starting point for any drawing you decide to do?

That's probably the best way to think about it when you're starting out. It's actually a bit more complicated than that, glTranslate shifts the entire coordinate system. Like I said though, for simple cases, think of it as though it moves a cursor that defines where you will draw.

And yes, the second triangle should cover up the first, unless you have some depth buffer weirdness going on.

Okay I think I understand Gltranslate finally. So when you change the x position your moving the entire coordinates to that one spot so really when you begin to draw you start at (0,0) even though technically youd be drawing a (1,0). Then with the rotating an object you simply change the point of view your drawing from and not the coordinates. But since you changed point of view you have to reset it using glLoadIdentity so that the other objects wont be affected by how the point of view was changed.

Is that basically right?

Quote:

Originally Posted by Shadowwoelf

Okay I think I understand Gltranslate finally. So when you change the x position your moving the entire coordinates to that one spot so really when you begin to draw you start at (0,0) even though technically youd be drawing a (1,0). Then with the rotating an object you simply change the point of view your drawing from and not the coordinates. But since you changed point of view you have to reset it using glLoadIdentity so that the other objects wont be affected by how the point of view was changed.

Is that basically right?

Basically, yes.

What glTranslate, glRotate, and glScale actually do is alter the transformation matrix. The transformation matrix is applied to everything you draw in order to determine how it should appear. glLoadIdentity resets the transformation matrix to an identity matrix, which doesn't modify any of your points. If you've ever done matrix math, some of that should make sense.