How to expand 3d lines when I click and drag in one end.
that’s quite an abstract question.
Would you be able to reproduce a scene you want to change? target your question a bit to help us understand what exactly you are referring to?
My scenario is linking two mesh with lines in 3D. If I move one mesh that linked line should need to expand. Is this clear?
I Create a line using,
BABYLON.Meshbuilder.CreateLines()
And I can’t able to get line points after creation, for change points to expand lines
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You should be able to get and set the vertices data as you can for other meshes: Updating Vertices | Babylon.js Documentation
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If you want to make the line longer, you can for example update the points array and call CreateLines() again to update the line length, like this 
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@labris I like your example connecting the meshes with lines when they’re clicked, but an issue is that it’s actually creating a new mesh each time without disposing of the old ones, since the existing mesh isn’t passed as the instance option. Also, the number of points can’t change when updating existing lines, only their positions can change. This can be verified via the inspector. 
But here is an updated example that properly disposes the old mesh before creating the new one with more points.
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Ooh, I gotcha now I think, here’s a simple example of updating the connecting line each time one of the mesh endpoints is dragged.
https://playground.babylonjs.com/#YEZPVT#837
Edit, it’s a little easier to just use the same position object for the meshes and line points, without the need to keep track of the index. 
https://playground.babylonjs.com/#YEZPVT#839
Ooh, one more edit, here’s a smoother version that fixes the issue of the line not updating right away when the mesh is dragged, by updating the line in the position validator instead of using the onDrag observable. It’s a little hacky since it’s not the intended usage of the validator, but the validator fires before rendering while onDrag fires afterwards, so it seems to works better in this case IMO. 
https://playground.babylonjs.com/#YEZPVT#840
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Lines and LineSystem are parametric meshes, so probably expandable in the way you want
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Drag Validator does the trick 
Really nice solution and it is possible to use any number of meshes - https://playground.babylonjs.com/#YEZPVT#850
I was curious about how long the line is so I added some position GUI markers - https://playground.babylonjs.com/#YEZPVT#849
There is also another drag implementation described in docs. From it I made this example - https://playground.babylonjs.com/#7CBW04#708
When I did the same with the tube I also added animation for donuts delivery - https://playground.babylonjs.com/#7CBW04#710
The effect was quite interesting, so I added some GLTF models, skybox, shadows, highlighting for picking wachtowers and, of course, some particles
Drag watchtowers in the top left viewport and see what happens in other views (Follow cam and 2 target cameras) - https://playground.babylonjs.com/#7CBW04#707
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