Feature Idea: Use characters in foreground of popup

[qbedard]

If we match the background color and insert characters into the popup window's buffer, would it be possible to create more complex shapes than the simple rectangle that results from relying on the window shape itself? Assuming there is not a way to control the fg/bg opacities separately, the background would still obscure text, but the visual effect should still work.

For example, if the buffer contains the actual characters and we simply change the buffer contents at each increment in the loop, then the effect could actually look like: ░░▒▒▓█████▓▒▒░░ ░▒▓███▓▒░ ░▒▓▒░

Thoughts?