BM_SETSTATE message

Sets the highlight state of a button. The highlight state indicates whether the button is highlighted as if the user had pushed it. You can send this message explicitly or use the Button_SetState macro.

wParam

A BOOL that specifies whether the button is highlighted. A value of TRUE highlights the button. A value of FALSE removes any highlighting.

lParam

Not used.

This message always returns zero.

Highlighting affects only the appearance of a button. It has no effect on the check state of a radio button or check box.

A button is automatically highlighted when the user positions the cursor over it and presses and holds the left mouse button. The highlighting is removed when the user releases the mouse button.

Reference

BM_GETSTATE

BM_SETCHECK