International
Tables for Crystallography Volume B Reciprocal space Edited by U. Shmueli © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. B. ch. 3.3, pp. 370-371
Section 3.3.1.3.7. Viewports
aMRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, England |
The window transformation of the previous two sections has been constructed to yield picture coordinates (X, Y, Z, W) (formerly called x, y, z, w) such that a point having or is on the boundary of the picture, and the clipping hardware operates on this basis. However, the edges of the picture need not be at the edges of the screen and a viewport transformation, V, is therefore needed to position the picture in the requisite part of the screen. where r, l, t and b are now the right, left, top and bottom boundaries of the picture area, or viewport, expressed in screen coordinates, and n is the full-screen deflection value. Thus a point with in picture space plots on the screen with an X coordinate which is a fraction of full-screen deflection to the right. is unchanged by V and is used only to control intensity in a technique known as depth cueing.
It is necessary, of course, to arrange for the aspect ratio of the viewport, , to equal that of the window otherwise distortions are introduced.