Drawing pictures brings up a series of problems, not all of which are evident at first. Scale and centering are among the most obvious, easily compensated by including provisions for moving the figure and changing its size. Conflicts can still remain, because excessive compression may make the figure difficult to read, or because the final result has to be presented on a sheet of paper of given size. The next remedy, but which REC-R does not use, is to divide a figure into panels, or use scrolling, at the price of increased programming complexity.
Rotation and reflection bring up new challenges, although some foresight can accomodate them as well. The simplest solution to figure revision is to introduce homogeneous coordinates, and subject all drawing operations to a projective transformation. Of course that implies matrix multiplication, which may or may not have a deleterious effect on performance. Computers are now sufficiently rapid that simple drawings can receive a fair amount of preprocessing while producing results compatible with human reaction time, which means about twenty frames per second.
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While projective facilities are easy enough to incorporate in newly written programs, they are noticeably lacking in such existing service programs as Draw with which the new programs may still want to interact.
For the moment, REC-R provides two parallel views, one in the phase window, shown in Figure 7, the other in the solution window shown in Figure 8. Both contain an image which may be copied into the pasteboard by invoking the ``Copy View'' button on the main menu (as seen in Figure 5) and then transferred into Draw by pasting. But so far, they lack any further processing.
