The routine gSelectDrawingArea() switches drawing to the selected drawing area. The default drawing area for all devices is 1, which represents the visible part of the screen or drawing media. On window devices, this identifier actually represents the backing store (or pixmap) which is automatically copied to the visible window through internal procedures. On such devices, selecting drawing area 0 may provided faster display times, but at the expense of possible display loss by the overlap of windows from other applications. Note that, drawing can be directed to the backing store only, through the operation of the gStartBatchUpdate()/gEndBatchUpdate() routines.
Additional drawing areas may be selected where these have been successfully opened using the routine gOpenAuxDrawingArea(). These auxiliary drawing area may be visible or invisible depending on whether the identifier is even or odd. All (even numbered) visible drawing areas will have an invisible drawing area associated with them (with the same operational criteria as the default drawing area as described above), but (odd numbered) invisible drawing areas may exist on their own. After selection, the current viewport and window limits are altered to match the size of the selected drawing area and the current point is reset to 0,0, but other GINO attributes remain unaltered.
The requested drawing area identifier must be within the permitted range for the currently nominated device and represent a valid opened area. Any invalid identifier will generate an error message and no change will be made to the currently selected area.
