nget-shape-line

Arguments: window-or-screen start-position old-position draw-fn erase-fn &optional scroll-p cursor

A destructive version of get-shape-line. The old-position argument is modified to be the endpoint position chosen by the user and then returned. Like get-shape-line, this function waits as the user moves the mouse about to establish the second endpoint (the first is start-position and cannot be modified by the user) of the desired line. When the user presses a mouse button to establish the endpoint, old-position is set to that position and returned. old-position must be a position (see make-position).

window-or-screen should be a window or the screen. The screen is the value returned by (screen *system*). See screen and *system*.

draw-fn should be a function object or a symbol naming a function, as should erase-fn. draw-fn is called each time the line is to be drawn and erase-fn is called each time it is to be erased. The draw-fn and erase-fn should each take three arguments: the window-or-screen, the start-position, and the mouse-cursor position. When they are called, the stream brush will be set to one pixel-width black, the stream paint operation to po-xor. Thus, drawing the shape twice will suffice.

As the mouse moves about, candidate lines are drawn and erased using draw-fn and erase-fn.

If scroll-p is true, the window identified by window-or-screen will be scrolled if the cursor moves outside it. Sets the stream cursor to cursor while running. If the cursor argument is t, a stream default is used (typically the cross-hair cursor).

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Created 2010.1.21.