I love RoundRects. They're great for motion design, or building mattes for all our favorite Apple devices.
A lot of design applications include tools specifically for creating RoundRects because, frankly, creating them from scratch is neither quick nor pleasant. But, since I do most of my design work in Nuke, the lack of easily-created RoundRects is a major pain point for me. So, like most of the tools and scripts on this site, while I wait for The Foundry to give us a proper RoundRect tool, I decided to build one myself.
The properties pane.
The most important part of any RoundRect tool is the ability to quickly and easily adjust the radius of the shape's corners. The Corner slider on my gizmo has a range from 0 (a square) to 2 (a circle), allowing me to dial in exactly the radius I need. The next thing it needed was the ability to make non-square RoundRects. The Width and Height sliders take care of just that.
Aside from the Size slider, I could have stopped there, but I figured I'd make it a bit more flexible and friendly while I was at it. Checkboxes give it the ability to be used as an alpha channel and, optionally, replace the existing alpha channel. The color slider is there for transparency adjustments and, of course, color.
Limitations
The standard transform controls are a no-brainer, but you will notice the lack of one particular transform parameter in the properties pane: scale.
The way this (hacky) gizmo is built, scaling must be done with the Size slider. Which means, despite the ability to grab the scale ring on the transform handle, don't. Scaling with the transform handle does not maintain resolution and edge quality when scaling up.
Fingers crossed that The Foundry will render this gizmo obsolete sooner rather than later, but, until then, happy RoundRect-ing.