| OCR Text |
Show *-••" p-w!'!»!»'!1"»'!1 """I" ••'w!fwviimwi^irf**imii..ii mvmf inn nuiui^ipwiBuppw^wwjiii»!*.«^"-"■i- ""j.,ini»iijij mum.vwi^fr^mmr^^fiumF- ■*****!*• in. u i m 10 TERMINATION The decision as to whether or not a subpatch should be subdivided is based on termination conditions. Two termination conditions will be discussed - size and clipping. For the purpose of this discussion we note that the terms "patch" and "subpf tch" can be used interchangeably, hence we will usually use the word "patch." As specified in th€' tgorithm, subdivision terminates when a patch covers only one sample-point. Since the «dues of a patch are curved, the test as to whether or not a Approximating polygon Patch Figure 2-5 patch covers only one sample-point may be time consuming. However, for the purpose of this test, a patch can be approximated by a polygon formed by connecting the four corners of the patch with straight line segments. The size of that polygon can then be checked to determine whether or not it covers at most one sample-point. This approximation should usually be adequaie for patches that are approaching the size of '-j>-*-MM^-i--^ ■ „^^-^^^ .. - , ... ■ ■■t:" |
