bottom-margin

Arguments: graphical-stream &optional (stream-units-p t)

Returns the current bottom margin of a graphical-stream, measured from the top edge of the stream. The bottom-margin is initially the page-height of the stream, except as noted below. (setf bottom-margin) may be called to set the margin at any time.

If stream-units-p is true, as it is by default, then the margin is measured in pixels. If nil, it is measured in text line heights (see line-height).

Margin attributes are provided primarily to allow an application to keep a drawing within arbitrary margins by drawing everything within the coordinates returned by left-margin, top-margin, right-margin, and bottom-margin. Common Graphics also uses them in a few special ways, though, as described below.

When drawing on a printer stream, typically an application should check whether the next thing that it is about to draw would extend past the bottom-margin. If so, then it should call new-page to tell the printer to move to a new sheet of paper, and then proceed to draw on the new page. The call to new-page will set the current-position-x of the stream to its left-margin and the current-position-y of the stream to its top-margin, so that text output will continue from the top of the new page. For other drawing functions, the application should adjust the coordinates at which it is drawing, generally by subtracting the page-length of the stream. The page-length is equal to the stream's top-margin subtracted from its bottom-margin.

A printer stream's coordinate system has position (0, 0) at the printer-physical-offset of the printer. To allow an application to avoid dealing with this arbitrary offset, Common Graphics sets the margins of a printer stream to the distance from the physical offset to the margins selected by the user in the print job dialog or page setup dialog. This allows the application to maintain the requested paper margins by simply drawing everything within the four margins that were set up automatically. See *default-printer-left-margin* for more information.

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Created 2010.1.21.