Period trace does wrong shape

[BryceAG]

Test device: Schrodinger Operating System: Windows 8 Browser: Chrome Problem description: When the weights do a full rotation counter clockwise the trace line bends awkwardly. does not happen with clockwise rotation. Steps to reproduce: set the pendulum to move, and mess with the gravity until it starts to do full rotations Severity:

Screenshots:

Troubleshooting information (do not edit): Name: ‪Pendulum Lab‬ URL: http://www.colorado.edu/physics/phet/dev/html/pendulum-lab/1.0.0-dev.8/pendulum-lab_en.html Version: 1.0.0-dev.8 2016-02-03 23:48:40 UTC Features missing: touch User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.111 Safari/537.36 Language: en-US Window: 1920x971 Pixel Ratio: 1/1 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: 1024 Texture: size: 8192 imageUnits: 16 (vertex: 16, combined: 32) Max viewport: 8192x8192 OES_texture_float: true Dependencies JSON: {"assert":{"sha":"d4909677","branch":"master"},"axon":{"sha":"3a5c7fb6","branch":"master"},"babel":{"sha":"cb55342f","branch":"master"},"brand":{"sha":"8c6f9c04","branch":"master"},"chipper":{"sha":"38916c91","branch":"master"},"dot":{"sha":"ddf82014","branch":"master"},"joist":{"sha":"4c228a32","branch":"master"},"kite":{"sha":"4a947119","branch":"master"},"pendulum-lab":{"sha":"07b907c0","branch":"master"},"phet-core":{"sha":"874a703d","branch":"master"},"phetcommon":{"sha":"3db92af3","branch":"master"},"scenery":{"sha":"d0753b38","branch":"master"},"scenery-phet":{"sha":"f02afc1a","branch":"master"},"sherpa":{"sha":"bf82eb95","branch":"master"},"sun":{"sha":"36a0486f","branch":"master"},"tandem":{"sha":"bfd87e0e","branch":"master"}}

related to phetsims/tasks#498

[jonathanolson]

When this occurs, Scenery throws an error:

Assertion failed: Not handling arcs with start/end angles that show differences in-between browser handling

It's trying to draw an arc with greater than 2pi of a rotation, so it will have browser-specific behavior (thus the weird appearance here).

[jonathanolson]

This is related to not fixing https://github.com/phetsims/pendulum-lab/issues/91.

@ariel-phet and @arouinfar, any opinions about interrupting the period trace (and possibly fading out) when the pendulum goes past the vertical line?

[ariel-phet]

@jonathanolson I would be fine if we decided to not show the period trace after the pendulum goes past the vertical line.

[arouinfar]

@jonathanolson I like @ariel-phet's suggestion. I think it will work nicely, and we'll avoid the issue of showing a period for something that doesn't technically have one.

[jonathanolson]

Done, closing.