Enable changing of corner roundness

[benrap]

How about an option to enable changing of corner roundness when choosing the square background?

[Maddoc42]

Yes, that would be great 👍 in fact, this could even replace the static option for square / round altogether and let the corner radius define how round the background is 🚀

Implementation should be "fairly" straight forward, roughly:

• Add slider UI similar to shadow length etc.
• Add listener to slider for reading corner radius. Values are between 0% and 100%, where 100% equals half the length of the background square which will create a perfect circle.
• From the listener update the background radius, making sure to rerender the shadow after each update (see other sliders as an example).
• Delete 'old' background UI option and remove associated code.

Am I missing something? 📝