VEraseOverlayLine - erases a 1-bit overlay line.
VEraseOverlayLine(win, ovl, x1, y1, x2, y2)
int x1, y1, x2, y2;
VEraseOverlayLine erases a 1-bit overlay line, in the image window or
one of its subwindows.
0 - work successfully.
1 - memory allocation error.
6 - invalid window ID.
225 - no overlay created.
237 - the overlay is not on.
win - the image window ID or one of its subwindows' ID.
ovl - specifies the overlay number to be used to ease the line.
x1, y1 - specifies the first point of the line.
x2, y2 - specifies the second point of the line.
Any other graphics in that overlay on that line will also be erased.
VTurnOnOverlay should be called first. If ovl, x1, x2, y1, or y2 is not
valid, or VCreateColormap is not called earlier VEraseOverlayLine prints an
error message to the standard error stream, produces a core dump file and
exits from the current process.