Can Point[ <Object>, <Parameter> ] be released?

zoltan shared this question 5 years ago

Answered

I would like to implement linkages in GeoGebra by disallowing positions of the constrained mover point which make no sense. My attempt is at https://www.geogebra.org/m/ZrwBFhYr. Here I restricted D to be freely draggable first, but when E is undefined, then D will be put to the last useful point. This is done by creating ppD=PathParameter[D] and for the on-update script of D the following JavaScript is started:

if (ggbApplet.getValue("x(E)")) {
var ppD = ggbApplet.getValue("ppD");
ggbApplet.evalCommand("ppDok="+ppD);
} else {
var ppDok = ggbApplet.getValue("ppDok");
ggbApplet.evalCommand("D=Point[d,"+ppDok+"]");
}

This fixes D when it is dragged to a disallowed position. Its position is OK now, but I want it to be draggable again. Is this possible somehow? Thanks for any hints in advance.

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Comments (9)

mathmagic ● 5 years ago

hello

I am not English and sometimes I do not understand some words

I suppose you want the attached

I have created some orange objects. see DM and O overall (DM instead D, O instead one intersection) I use two intersect points of circle ever

saludos

Files: foro.ggb

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zoltan ● 5 years ago

That's very clever. Not a solution in general, but for this particular example it's perfect. Thank you!

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mathmagic ● 5 years ago

Not a solution in general, but for this particular example it's perfect.

I think more general than others

https://www.geogebra.org/m/Drbxq9Y5

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zoltan ● 5 years ago

Unfortunately I found a bug in GeoGebra in positioning a point to a union of two overlapping paths. In the attached example ppDM (the PathParameter for DM) is 0.05, but if I drag DM very carefully to a different position, it may be very suddenly 0.95. That is, by continuously dragging DM you cannot expect that the PathParameter will be continuously changed in the attached case. This results in jumping positions of O. This behavior does not occur very frequently, however.

Files: wrong-jump.ggb

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mathmagic ● 5 years ago

hello again

try this code

if (ggbApplet.getValue("x(E)")) {
var ppD = ggbApplet.getValue("ppD");
ggbApplet.evalCommand("ppDok="+ppD);
} else {
var ppDok = ggbApplet.getValue("ppDok");
ggbApplet.evalCommand("SelectObjects[]");
ggbApplet.evalCommand("SetValue[D,Point[d,"+ppDok+"]]");
}

then you will want another point like D for the other half of curve

saludos

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zoltan ● 5 years ago

This is exactly I was searching for! That's wonderful. Thank you so much! :-)

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mathmagic ● 5 years ago

I think you can do the script in GGscript

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zoltan ● 5 years ago

Yes, maybe it's possible in simple GGscript also. Now I added an extra idea by computing the ordinal of the intersection. This one cannot be animated, just dragged.

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mathmagic ● 5 years ago

hello

select DM and walk slowly around arcs over the vectorial path

/OwAAAABJRU5ErkJgggA=

0<=pathparameter[]<=1 so 0.05 and 0.97 are near pathparameter values

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