In my particular case, I want to use it as a way to highlight things in the UI. I created a texture that is black with a soft hole in the center. I position the sprite where I want to highlight something (imagine a tutorial pointing out certain features), with partial transparency applied so it looks like the screen darkens except where the hole is. However, the black edges of the sprite end at the edge of the sprite instead of covering the whole screen.
I am able to do this with my own custom quad with edge repeat enabled for the texture, but the material/shader I use for it doesn't play well with some NGUI elements for blending. Some NGUI elements simply disappear behind the non-transparent part of the texture.
I've attached a screenshot to help you visualize what I'm talking about. The technique in the screenshot is actually the spotlight sprite surrounded by black sprites, but on some PC's you can see a small gap between the sprites, particularly when the sprites are scaled larger than actual pixel size (which is necessary to get various spotlight sizes).
