How to write a GUI function/command in gVim?

Question

I only found three types of dialog in gVim:

:let n = inputdialog("value for shiftwidth", &sw)
:call confirm("Save changes?", "&Yes\n&No\n&Cancel")
:browse e

Can I write a GUI Dialog, such as a ColorPick-Dialog to choose RGB value?
Does gVim support custom GUI widget?

Answer 1

No, it is not possible.

However you can make up your own DLL and libcall(). If your library must return a string (pointer to a zero-terminated array of characters) it will leak.