There is only one transformation between the page coordinate space and the device space, the device transformation. The device transformation enables applications to work in any presentation-page units regardless of the target device. Unlike the transformations previously described, the device transformation only scales and translates objects, and it is defined by two rectangles.
The first rectangle is called the presentation page. Its location is the bottom left origin and its dimensions are fixed. The second is called the page viewport. Its location is the bottom left origin and its dimensions can be varied.
The device transformation, which maps the picture in presentation-page space to device space, happens automatically. The device transformation is established when the presentation space is created, and ensures that graphics are displayed in the correct size and, where possible, that their aspect ratio is preserved.
To modify the device transformation, applications use GpiSetPageViewport. Input for this function is the device coordinates of the lower-left and upper-right corners of the page viewport. Applications should modify the default device transformation only when it is necessary to use nonstandard page units.