transparent-character-background

Arguments: window

Returns (or sets with setf) whether the "empty" areas of a character will be left as they were when they are drawn. If nil (which is the default), then drawing a character on the window will also draw the window's background color to fill the parts of the character cell that are not drawn in the foreground color to form the character. If true, then these empty areas will be left alone, so that any content that was previously drawn on the window will show through the characters.

Note: in earlier versions of the documentation, this function was documented to work with dashed lines as well as characters. That was incorrect. This function does not work with dashed lines.

The value is important for functions like draw-string-in-box.

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Created 2010.1.21.