Rotate the object around with its center point in OpenGL?

[z45li]

I have a robot, and I’ve determined the center point at (0.5f, 0.0f, -1.0f) . I’m trying to rotate the robot around its center point, I know that I need to translate the point to the origin first, rotate, translate back to the center. My robot can rotate around its center now, but when I moving the robot, it won’t be able to rotate around its center.

I did research, I need to figure out the current forward direction vector of my bot and update that vector every time when I moving my robot. I did the calculation and got the direction vector. However, I don’t know how to implement that into OpenGL.

Here is my code:

void drawRobot()
{

     glPushMatrix();

     glTranslatef(0.5f,0.0f,-1.0f);
     glRotatef(robotAngle, 0.0, 1.0, 0.0); //default robotAngle is 0
     glTranslatef(-0.5f, -0.0f, 1.0f);

     drawBase();
     drawWheel();
     drawWeapon();

     glPopMatrix();
}

[GClements]

If you’re implementing a self-propelled entity (vehicle, person, whatever), you should probably be calculating its motion in the application and just passing the final transformation to OpenGL via glLoadMatrix or glMultMatrix.