Merge pull request #397 from recp/affine-docs

clarify some rotation rules

docs/source/affine-pre.rst

@@ -110,7 +110,24 @@ Functions documentation
 
 .. c:function:: void  glm_rotate(mat4 m, float angle, vec3 axis)
 
-    rotate existing transform matrix around Z axis by angle and axis
+    rotate existing transform matrix around given axis by angle at ORIGIN (0,0,0)
+
+    **❗️IMPORTANT ❗️**
+    
+    If you need to rotate object around itself e.g. center of object or at
+    some point [of object] then `glm_rotate_at()` would be better choice to do so.
+    
+    Even if object's model transform is identiy, rotation may not be around
+    center of object if object does not lay out at ORIGIN perfectly.
+    
+    Using `glm_rotate_at()` with center of bounding shape ( AABB, Sphere ... )
+    would be an easy option to rotate around object if object is not at origin.
+    
+    One another option to rotate around itself at any point is `glm_spin()`
+    which is perfect if only rotating around model position is desired e.g. not
+    specific point on model for instance center of geometry or center of mass,
+    again if geometry is not perfectly centered at origin at identity transform,
+    rotation may not be around geometry.
 
     Parameters:
       | *[in, out]* **m**     affine transform