The _lineto functions draw a line from the current position up to and
including the destination point. The destination point for the _lineto
function is given by the view coordinate point (x, y). The destination
point for the _lineto_w function is given by the window coordinate-point
(wx, wy).
The _lineto_w function is implemented as a macro.
The line is drawn using the current color and line style. If no error
occurs, _lineto sets the current position to the view point (x, y);
_lineto_w sets the current position to the window point (wx, wy).
----- Note -----
If you use _floodfill to fill in a closed figure drawn with _lineto calls,
the figure must be drawn with a solid line-style pattern.
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Return Value
The _lineto and _lineto_w routines return a nonzero value if the line is
drawn successfully; otherwise, they return 0.