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Normalized Device Coordinates

Where do we specify our viewport?
Could specify it in device coordinates ...
BUT, suppose we want to run program on several hardware platforms or graphic devices.
Two common conventions for DCS:
- Origin in the lower left corner, with x to the right and y upward.
- Origin in the top left corner, with x to the right and y downward.
Many different resolutions for graphics display devices:
- Workstations commonly have 1280 1024 frame buffers.
- A PostScript page is 612 792 points, but 2550 3300 pixels at 300dpi.
- And so on ...
Aspect ratios may vary ...
If we map directly from WCS to a DCS, then changing our device requires rewriting this mapping (among other changes).
Instead, use Normalized Device Coordinates (NDC) as an intermediate coordinate system that gets mapped to the device layer.
Will consider using only a square portion of the device.
Windows in WCS will be mapped to viewports that are specified within a unit square in NDC space.
Map viewports from NDC coordinates to the screen.

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Reading: Hearn and Baker: Sections 2-7, 6-3 Red book: 6.3. White book: 6.5