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Opengl rotates always around (0,0,0). But I need to rotate around the camera. I know that in GL, there is no camera, but if I translate back to (0,0,-6.0) , it rotates around (0,0,0), not around (0,0,-6.0)

So my question is : How to set the rotation centre in opengl and c++

I already found this post : OpenGL rotating a camera around a point

Where this solution is showed :

rotation functions normally rotate about the origin. To rotate around another point P you have to: translate(-P) rotate translate(P)

And I dont now how to realize the

translate(P)

because after the rotation the translation is relative to the rotation

Example : I want to rotate around (1,1,1). I translate (-1,-1,-1). Now I rotate it around the x-axis by 90 degrees. Its right. But now I have to translate it back. If I translate (1,1,1), it wont work, because its now rotated, and the movement is relative to the rotated matrix.

PS : I dont want to use gluLookAt()

So my code would be : 

//set rotation to zero
glRotatef(-yr,0.0f,1.0f,0.0f);  
glRotatef(-xr,1.0f,0.0f,0.0f);
//set points relative to camera
glTranslatef(cam_pos[0],cam_pos[1],cam_pos[2]);
//rotate back
glRotatef(yr,0.0f,1.0f,0.0f);   
glRotatef(xr,1.0f,0.0f,0.0f);
//rotate
glRotatef(angley,0.0f,1.0f,0.0f);   
glRotatef(anglex,1.0f,0.0f,0.0f);
//and now, how to translate back,
//movement is relative to the cam ?
//I would simply use :  
//glTranslatef(-cam_pos[0],-cam_pos[1],-cam_pos[2]);
//which wont work because its relative to the new rotation.

Any help is greatly appreciated !

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Luatic
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  • What you say is just not true, even if written in bold face, and asked for the second time. You got the math backwards, and have some misconceptions of how GL's matrix stack works. I recommend you to grab a good book on linear algebra. And, I'd recommed you to also drop this horrible outdated GL you are trying to use here. – derhass Jan 22 '17 at 18:23
  • I could get it working, if I would find out how to move back. Thats my only problem. – Luatic Jan 22 '17 at 18:31
  • You _aready_ move it "back" (kind of - just not in the right direction, and with weird "reset rotation" inbetween). You actually don't move it _before_ the rotation. As I said, you got the math _backwards_. – derhass Jan 22 '17 at 18:36
  • ok, thanks for the advice – Luatic Jan 22 '17 at 19:03

1 Answers1

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So, I actually figured out that movement isnt relative to rotation, what makes everything easy to realize. Code : 

glTranslatef(point_to_rotate_around_x,point_to_rotate_around_y,point_to_rotate_around_z);
glRotatef(anglex,1,0,0);
glRotatef(angley,0,1,0);
glTranslatef(-point_to_rotate_around_x,-point_to_rotate_around_y,-point_to_rotate_around_z);

Thanks @derhass, who told me that its backwards.

Luatic
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