non square window and non square button

[j_f laposte net]

Hi guys,
I want to create a little UI that has a non square window and non square
button, in fact I want to map image inside button and window, something
like the xine UI for exemple, but i can't achieve this goal, does anyone
ever did this ?
please give me any pointer or exemple
thanks
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  <j_f laposte net>