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Re: Slow Locator in Manipulate

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  • Subject: [mg126615] Re: Slow Locator in Manipulate
  • From: "Kevin J. McCann" <kjm at>
  • Date: Fri, 25 May 2012 04:57:32 -0400 (EDT)
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  • References: <jpi3lf$4rt$>

Thanks to David Park, E. Martin-Serrano, and Fred Simons for responses.

The work around for this seems to be to use a Rasterized image of the 
figure. It is not at all clear to me why this should be more CPU 
efficient, but there is little or no documentation that helps. A lengthy 
tutorial with examples on how Dynamic and its relatives work with 
graphical output would be a big plus.


On 5/23/2012 3:29 AM, Kevin J. McCann wrote:
> The following is a simple example of the use of a Locator on a graphic:
> p1 = ContourPlot[
>      Sin[x y], {x, -3 \[Pi], 3 \[Pi]}, {y, -3 \[Pi], 3 \[Pi]},
>      ContourShading ->  False];
> Manipulate[
>    Show[p1, Graphics[{Red, AbsolutePointSize[5], Dynamic@Point[pt1]}],
>     PlotRange ->  {{-3 \[Pi], 3 \[Pi]}, {-3 \[Pi], 3 \[Pi]}}],
>    {{pt1, {0, 0}}, {-3 \[Pi], -3 \[Pi]}, {3 \[Pi], 3 \[Pi]}, Locator}
>    ]
> I find that the Locator moves slowly and in a jerky fashion; however, if
> I leave the underlying plot, i.e. p1, out of the Show, then it moves as
> I would expect. I had thought the use of Dynamic on the Point would keep
> Mathematica from constantly redrawing the graphic, but my guess is that the
> slowness indicates this is not the case.
> Anyone have an idea about how to make the locator move faster?
> Thanks,
> Kevin

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