Source code

<action name="dragrotation_hs">
		<!-- backup current align/edge settings -->
		copy(backup_align, align);
		copy(backup_edge, edge);
		
		<!-- change the origin to lefttop to get coordinates relative to the mouse -->
		changeorigin(lefttop,center);

//adapting code for hotspots...

copy(hsath, hotspot[get(name)].ath);
copy(hsatv, hotspot[get(name)].atv);

spheretoscreen(hsath,hsatv,xath,yatv);

copy(mx, xath);
copy(my, yatv);

// end adapting
		
		<!-- restore the align/edge settings -->
		changeorigin(get(backup_align),get(backup_edge));
		
		<!-- calc the start rotation -->
		sub(dx, mx, mouse.stagex);
		sub(dy, my, mouse.stagey);
		Math.atan2(r, dx, dy);
		div(r, Math.PI);
		mul(r, 180.0);
		add(sr, rotate, r);
		
		<!-- loop as long as the mouse button is pressed and rotate the image -->
		asyncloop(pressed,
			sub(dx, mx, mouse.stagex);
			sub(dy, my, mouse.stagey);
			Math.atan2(r, dx, dy);
			div(r, Math.PI);
			mul(r, 180.0);
			sub(rotate, sr, r);
		  );
	</action>

Source code

<hotspot name="hs_spot1" sedge="center"  align="center" rotate="0"  ath="0.175" atv="0.072" ondown="dragrotation_hs"/>