GDDMXD supports four graphics presentation space sizes. The size of the graphics presentation space used by GDDMXD is determined by the window width specified by the Geometry option in the user_id.X.DEFAULTS data set (see GDDMXD/MVS: User-specified options for more information). The size is also determined dynamically when you resize the GDDMXD graphics window. The relationship between the size of the graphics presentation space and the window width is shown in Table 1.

For graphics presentation space sizes other than the default size (720 pixels by 512 pixels), bit-mapped data, such as symbol sets and images, is expanded or compressed to meet the scaling requirements of the specified graphics presentation space.

You can expand bit-mapped data by duplicating rows and columns of the data. The resulting view can differ slightly from the default-size view. You can compress single-plane bit-mapped data by combining rows and columns of the data with a logical OR function. Because this might not yield acceptable results when a black on white image is viewed, the Compr option is provided to specify that a logical AND function be used to compress the data. See Compr option—Control the technique used to compress bit-mapped data for more information about using this option. You can compress multiplane bit-mapped data by eliminating certain rows and columns. Data compression produces a view that is different from the default-size view.