Learn if a button is pressed (or released).
The MUIA_Pressed attribute of a gadget is triggered
by some user action, depending on the input mode:
- MUIV_InputMode_RelVerify:
- set when lmb is pressed.
- cleared when lmb is released and the mouse is still over the gadget (otherwise it will
be cleared too, but without triggering a
notification event).
- MUIV_InputMode_Immediate:
- undefined, use MUIA_Selected for this.
- MUIV_InputMode_Toggle:
- undefined, use MUIA_Selected for this.
Waiting for MUIA_Pressed getting FALSE is the usual
way to react on button gadgets.