I represent a viewport for the Ballon 3D graphics engine. Since all positions are computed in the unit-coordinate system (-1,-1,-1) (1,1,1) after the render pipeline has completed, I am used to map these positions into the physical (pixel) coordinates of the output device before rasterization takes place.

Instance variables:
center <Point> The center of the viewport
scale <Point> The scale for points

	mapping
	asMatrixTransform2x3 mapVertex2: mapVertex4:

	private
	setOrigin:corner: toggleYScale

	accessing	top
	aspectRatio
	center Answer the point at the center of the receiver.
	scale

	mapping	top
	asMatrixTransform2x3
	mapVertex2:
	mapVertex4:

	private	top
	setOrigin:corner:
	toggleYScale