MASK_CLICK
if ((sp->_mouse_mask2 & MASK_CLICK(b))
next->bstate |= MASK_CLICK(b);
&& (ep->bstate & MASK_CLICK(b))
&& (next->bstate & MASK_CLICK(b))) {
next->bstate &= ~MASK_CLICK(b);
&& (next->bstate & MASK_CLICK(b))) {
next->bstate &= ~MASK_CLICK(b);
SP_PARM->_mouse_mask2 |= MASK_CLICK(b);
if (SP_PARM->_mouse_mask2 & MASK_CLICK(b))