CXT105@psuvm.psu.edu (Christopher Tate) (04/17/91)
Does binding the procedure argument to setscreen have any effect? I.e. is
85 35 {dup mul exch dup mul add 1.0 exch sub} bind setscreen
equivalent in function to
85 35 {dup mul exch dup mul add 1.0 exch sub} setscreen ?
Does binding the spot function give incorrect results? If not, it seems
like binding it should give an appreciable savings in speed, since it's
called often. Or, it could be that the setscreen operator binds it itself,
or some other part of the imaging system does. In that case, binding it
would have essentially no effect....
Which of the above is correct? :-)
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Christopher Tate |
Student-Type Person | "The whole place is coming alive!"
cxt105@psuvm.psu.edu |
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cxt105@psuvm.bitnet |deadman@garnet.berkeley.edu (Ben Haller) (04/17/91)
In article <91106.223332CXT105@psuvm.psu.edu> Christopher Tate <CXT105@psuvm.psu.edu> writes: >Does binding the procedure argument to setscreen have any effect? I.e. is > 85 35 {dup mul exch dup mul add 1.0 exch sub} bind setscreen >equivalent in function to > 85 35 {dup mul exch dup mul add 1.0 exch sub} setscreen ? >Does binding the spot function give incorrect results? If not, it seems >like binding it should give an appreciable savings in speed, since it's >called often. Or, it could be that the setscreen operator binds it itself, >or some other part of the imaging system does. In that case, binding it >would have essentially no effect.... Well, I don't claim to know very much about this. But it's my impression that PostScript takes the setscreen parameters, and immediately converts that into an internal format that's much faster to use (and may be of a different frequency, angle, etc, as explained in the book _Real World PostScript_). So the spot function would be called perhaps several hundred times, the results would be tabulated and sorted, resulting in some internal pattern format for the halftone patterns. So my answer is, it shouldn't matter unless you're changing the spot function often, like within a larger loop. To answer the original question, I don't know if it hurts to bind it (I don't imagine it does, but I have no idea really), and I don't know if it would speed up that initial tabulation process or not. Why not try it? -Ben Haller (deadman@garnet.berkeley.edu) "Sleeping with your devil mask / Is all I wanna do And when I stop, it means I'm through with YOU! Yeah, yeah you. " - Robyn Hitchcock
andrew@visix.com (Andrew Bernard) (04/18/91)
In article <91106.223332CXT105@psuvm.psu.edu> CXT105@psuvm.psu.edu (Christopher Tate) writes: >Does binding the procedure argument to setscreen have any effect? I.e. is > > 85 35 {dup mul exch dup mul add 1.0 exch sub} bind setscreen > >equivalent in function to > > 85 35 {dup mul exch dup mul add 1.0 exch sub} setscreen ? > >Does binding the spot function give incorrect results? If not, it seems >like binding it should give an appreciable savings in speed, since it's >called often. Or, it could be that the setscreen operator binds it itself, >or some other part of the imaging system does. In that case, binding it >would have essentially no effect.... > >Which of the above is correct? :-) > It shouldn't give different results unless you've got a dictionary on the dict stack which shadows the normal operator bindings. As far as speed, it probably won't make any difference, since a good interpreter will compile the results of the samples into its own internal matrix. So, I suspect the sample procedure will only get called once for each pixel in the halftone square, no matter how many times you render with it. Of course, if you're changing the screen a lot, I suppose it could have an impact on performance, but that's an unusual case. BTW, a good interpreter will do a similar optimization for _settransfer_: the procedure gets called once for each possible grey value (this is limited by the interpreter's internal color representation and the size of the halftone spot) and the results are stuffed into an array which is used later to look up the actual color values. Try putting _print_ operators into your screen procs and you can tell how often they get called. -- andrew bernard ring the doorbell on your mind software engineer but it's locked from the outside visix software -dinosaur jr. andrew@visix.com