Ethan A Merritt wrote:
> In gadgets.c we have the very nice clipping routines:
> clip_line() draw_clip_line()
>
> In graphics.c we have a separate collection of very specialized
> but also rather complicated routines:
> edge_intersect() two_edge_intersect()
> edge_intersect_steps() edge_intersect_fsteps()
> two_edge_intersect_steps() two_edge_intersect_fsteps()
>
> Is this a code duplication due to historical artifact?
Not really. The /.*edge_intersect.*/ routines clip in ways specific to
individual plot styles, governed at least partly by the
INRANGE/OUTRANGE/UNDEFINED information from function/data parsing. At
least the UNDEFINED flag is not available in any other way, so it has
to be like that. And checking INRANGE / OUTRANGE flags is faster than
calling a generic clipper every iteration of a (possibly loong) list of
data points.
These are not really just clipping routines for individual edges;
they're parts of the plot routines for outputting plots in a correctly
clipped way. That's why steps and fsteps get their own clippers, and
why these clippers work in data coordinates (floating point), not in
terminal integers.
> At first glance all of the 100-200 line *_edge_intersect_* routines
> appear to do essentially the same thing as a simple series of calls
> to clip_line().
Yes. But there are differences, and IIRC, some of those are somewhat
easy to miss on casual reading. BTDT years ago.
> Many code sections in graphics.c and graph3d.c test and sort line
> segments
I don't recall any sorting being involved.
> by the inrange/outrange property of their endpoints,
> and then call these single-purpose *_edge_intersect_* routines to
> perform clipping.
... and they do that *only* in those case where it's actually needed.
That's an important aspect of how that's being done.
> I am wondering if these sections can be simplified
> dramatically by instead drawing all of the individual segments via
> draw_clip_line().
I don't think so. Doing this in data space, on floats, has some
advantages that would be lost if you did this in terminal coordinates.
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