Custom tool to use the mouse to rotate a grid in an image window.

This tool allows the user to set the angle of roation of a grid overlying a given rectangle of the image window. The grid is rotated by interactively dragging the mouse in a circular motion with the mouse.

When invoked on an McGraphOverlay that is being displayed in an IMcView, the tool shows a curved arrow icon whenever the cursor passes into the viewed client window. When the left mouse button is pressed and held (or mcrgtcfStartRotateGrid is assigned to CommandFlags), then the angle of the displayed grid is set to track movement of the cursor until the left mouse button is released (or mcrgtcfStopRotateGrid is assigned to CommandFlags).