comp.lang.idl-pvwave archive - RDF feed
type: channel
description: Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
items: Re: Object graphics questions and comment

Re: Object graphics questions and comment
type: item
description: Paul van Delst is trying to draw a zoom-box using object graphics. He writes: > Anyway, I create a zoom box on a left button down event, add it to my > plot_model and draw the resulting view. [ Details deleted] > Now all this works great. I get a lovely zoom box except IT IS SOOOOO > SLOW? I test my code on a 1000 element data set and the zoom box can't > keep up with the mouse motion events. Increase the number of points and > it's unusable. > > MY QUESTIONS: Is the snail pace response implicit of IDLs of object > graphics (another e.g. IDLs Insight. Good lord) or is there another way > to do this without having to do a > (*info_ptr).window -> draw, (*info_ptr).view > every time? In Direct Graphics you simply erase ONLY the box and then > redraw ONLY the new box, you don't redraw the entire view. Can this be > done using Object Graphics? The documentation is obtuse and unhelpful. Paul, I am VERY sympathetic. I even thought seriously about dropping everything and working on an example for you, but I have promised my wife that I would work EXCLUSIVELY on my IDL book this month in the hope that some income might be generated...soon! :-) But, IF I were going to do this, I would try it in a slightly different way. Rendering graphics objects is inherently slower than rendering direct objects. Techniques that worked with direct graphics will have to be modified or completely re-invented to work with object graphics. I'm not sure anyone has all the answers right now. In direct graphics, the zoom box was drawn and erased, over and over, by using a pixmap and the DEVICE COPY technique (usually). I think the preferred technique in object graphics will be to have the unchanging parts of the graphics window in one model and the changing parts (e.g. the zoom box) in another. Then you can make an INSTANCE of the unchanging model. You can think of this as a snapshot of the unchanging part of the scene. (Kind of like the role of the pixmap, previously.) This snapshot can be rendere…
creator: davidf
date: 1997-08-11T07:00:00-00:00