3 ms·

I'd wondered that as well. Playing with tldraw and excalidraw, it looks like it's using the center of the bounding box as the pivot point. Suppose that you ha

by a_e_k 5y ago

I'd wondered that as well. Playing with tldraw and excalidraw, it looks like it's using the center of the bounding box as the pivot point. Suppose that you have three boxes like this: * - - - * . . . * - - - * | | | | | | | | | | | | * - - - * * - - - * . . . @ . . . . * - - - * . | | . | | . | | . . . . . . . . * - - - * The pivot for rotating them will be at the @ in the center of the bounding box around the three. If you then turn that counterclockwise by 45 degrees: . . . . . . . . . * . . . . . . . . . . / \ . . / \ . . * * . . \ / . . \ / . . * @ * . . / \ / \ . . / \ / \ . * * * * . \ / \ / . . \ / \ / . . . . * . . . . . . . . . . . * . . . then the center of the bounding box has now moved towards the corner of what was originally the upper right square (because there isn't a fourth square to complete the symmetry and push the bottom of the box around the three squares down). Rotating again will now pivot around this new point rather than the original and a rotation 45 degrees clockwise back to the original angle will now have shifted the boxes. Honestly, I'd think the correct solution here would be to pivot around the center-of-mass or some other rotationally-invariant point.

kingcharles 5y ago
Forget the article, I'm more impressed by your ASCII art.
iainmerrick 5y ago
The bounding box is the natural implementation because it matches what the user sees -- when you select multiple objects, the rotation handle is at the corner, because where else would it be? Plus it’s very easy to code and to test. But yeah, using a rotationally-invariant point would be better than the stateful fix the article goes for. Center-of-mass would make sense except it might do strange things if you have a mix of solid shapes and lines. How much mass should the lines have? Using the centre of the bounding circle is probably best, as others in this discussion have suggested.

by a_e_k 5y ago

kingcharles 5y ago

Forget the article, I'm more impressed by your ASCII art.

iainmerrick 5y ago

The bounding box is the natural implementation because it matches what the user sees -- when you select multiple objects, the rotation handle is at the corner, because where else would it be? Plus it’s very easy to code and to test. But yeah, using a rotationally-invariant point would be better than the stateful fix the article goes for. Center-of-mass would make sense except it might do strange things if you have a mix of solid shapes and lines. How much mass should the lines have? Using the centre of the bounding circle is probably best, as others in this discussion have suggested.