OpenGl绕点旋转

Question

My problem is that I need to rotate a white square around the center of the far left end, and no matter what I try, I cannot seem to do it.

I need to rotate an object around radius , which is radius far from the position ( getPosition().x/y ), which i have already translated to. I need to rotate it r degrees. If it matters, I am using an orthographic ( glOrtho ) projection.

So far this what I tried:

//Try 1
glRotatef(r, 0, 0, 1.0f);
glTranslatef(radius, radius, 0);
glBegin(GL_QUADS)
//draw here...

//Try 2
glTranslatef(-radius, -radius, 0);
glRotatef(r, 0, 0, 1.0f);
glTranslatef(radius, radius, 0);
glBegin(GL_QUADS)
//draw here...

//Try 3
glTranslatef(radius + getPosition().x, radius + getPosition().y, 0);
glRotatef(r, 0, 0, 1.0f);
glTranslatef(radius, radius, 0);
glBegin(GL_QUADS)
//draw here...

I have tried Googling and searching on StackOverflow numerous times, with no luck. Two of these "solutions" came from answers found on StackOverflow itself.

All of these attempts rotate around the origin. I have also tried numerous other more nonsensical combinations, to no avail. If it matters, a little bit before this code, I translate the matrix (and don't pop it back out). I don't think this is the problem, as popping the matrix and pushing a new one back on right before any of these attempts does not fix the problem.

Any help would be much appreciated.

Answer 1

So I found the solution:

glTranslatef(radius + getPosition().x, radius + getPosition().y, 0);
glRotatef(r, 0, 0, 1.0f);
glBegin(GL_POLYGON);

It turns out you dont have to translate after the rotation, which is was several sources suggested.