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webgl rotate an object around another object in one axis


I think you need to do a sequence of matrix operations and the order of matrix operation matters.

What you probably want in this case is to first translate Mercury to position of Sun, then do the rotation, then reverse the first translation. I have not yet implemented hierarchical objects myself so I dont want to confuse you. But here is the code for my implementation of orbit camera which the yaw function rotates the camera around a target point and you may find it useful:

 yaw: function(radian){
        this.q = quat.axisAngle(this.q,
this.GLOBALUP, radian);
        vec3.rotateByQuat(this.dir, this.dir,
this.q);
       
vec3.cross(this.side,this.GLOBALUP,this.dir);
        vec3.normalize(this.side,this.side);

        this.pos[0] = this.target[0] - this.dir[0]
* this.dist;
        this.pos[1] = this.target[1] - this.dir[1]
* this.dist;
        this.pos[2] = this.target[2] - this.dir[2]
* this.dist;
}

Where this.dir is a normalized vector that always gives the direction from Camera to target and this.dist is the distance between camera and target. You can use matrix rotation instead of quaternion rotation.

Edit: just to add the direction can be calculated by taking the difference in position of the two objects then normalize it.


Categories : Javascript

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