set_has_alpha
Description:
If has_alpha is true the buffer allocated by the widget will have an alpha channel component,
and when rendering to the window the result will be composited over whatever is below the widget.
If has_alpha is false there will be no alpha channel, and the buffer will fully replace anything
below the widget.
Parameters:
| this |
a GLArea |
| has_alpha |
true to add an alpha component |