Kink/Loop in track after making a connection

[KatieWoe]

Test Device: Dell Laptop Operating System: Windows 10 Browser: Chrome Problem description: When connecting two pieces of track one of the points will shift and cause a kink or loop in the track, instead of a smooth curve. For phetsims/QA/issues/134 Steps to reproduce:

1. Go to the playground screen
2. Manipulate the first piece of track so that it is a sharp bowl shape opening to the left.
3. Select a new piece of track and place it to the left of the bottom piece of the existing track but do not connect them yet
4. Drag the middle point of the new track down to form a gentle curve
5. Connect the two pieces of track Screenshots:

Troubleshooting information (do not edit):

Name: ‪Energy Skate Park: Basics‬ URL: https://phet-dev.colorado.edu/html/energy-skate-park-basics/1.4.0-dev.1/phet/energy-skate-park-basics_en_phet.html Version: 1.4.0-dev.1 2018-06-20 00:09:06 UTC Flags: pixelRatioScaling User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36 Language: en-US Window: 1536x741 Pixel Ratio: 2.5/1 WebGL: WebGL 1.0 (OpenGL ES 2.0 Chromium) GLSL: WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium) Vendor: WebKit (WebKit WebGL) Vertex: attribs: 16 varying: 30 uniform: 4096 Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 32) Max viewport: 16384x16384 OES_texture_float: true Dependencies JSON: {"assert":{"sha":"928741cf","branch":"master"},"axon":{"sha":"f0522e7c","branch":"master"},"brand":{"sha":"89d28f63","branch":"master"},"chipper":{"sha":"e8946524","branch":"master"},"dot":{"sha":"6482f8c9","branch":"master"},"energy-skate-park-basics":{"sha":"288fcefd","branch":"master"},"joist":{"sha":"22e437d5","branch":"master"},"kite":{"sha":"a1086efc","branch":"master"},"phet-core":{"sha":"17326041","branch":"master"},"phet-io":{"sha":"3ea0727a","branch":"master"},"phet-io-wrapper-classroom-activity":{"sha":"53708616","branch":"master"},"phet-io-wrapper-hookes-law-energy":{"sha":"8a546a32","branch":"master"},"phet-io-wrapper-lab-book":{"sha":"1527afd6","branch":"master"},"phet-io-wrappers":{"sha":"8d814eab","branch":"master"},"phetcommon":{"sha":"6ec8cd89","branch":"master"},"query-string-machine":{"sha":"4182612f","branch":"master"},"scenery":{"sha":"88cb642e","branch":"master"},"scenery-phet":{"sha":"7bcde0b2","branch":"master"},"sherpa":{"sha":"88c3b828","branch":"master"},"sun":{"sha":"7579e8fa","branch":"master"},"tandem":{"sha":"8461b6f3","branch":"master"}}

[jessegreenberg]

Thanks for reporting @KatieWoe. @ariel-phet is this a bug, and if so does it need to be fixed for the LoL/phetio release?

[jessegreenberg]

I don't think this is a bug personally, just the behavior of the cubic splines.

[ariel-phet]

@KatieWoe @jessegreenberg I also do not think this is a bug, especially since it does not create a super sharp kink. I think this can be closed.