Small atoms can be hard to grab with touch

[KatieWoe]

Test device
Dell
Operating System
Win 10
Browser
chrome
Problem description
For phetsims/qa#459
When your finger drags part of the screen when not starting on an atom, a cutting action is done. However, this means that dragging to pick up an atom doesn't work. This makes the margin of error for picking up an atom, particularly a small one, smaller.

Visuals

Troubleshooting information:

!!!!! DO NOT EDIT !!!!!
Name: ‪Build a Molecule‬
URL: https://phet-dev.colorado.edu/html/build-a-molecule/0.0.0-dev.23/phet/build-a-molecule_all_phet.html
Version: 0.0.0-dev.23 2019-11-20 23:29:39 UTC
Features missing: touch
Flags: pixelRatioScaling
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.97 Safari/537.36
Language: en-US
Window: 1536x722
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: 32767x32767
OES_texture_float: true
Dependencies JSON: {}

[Denz1994]

A grabbable offset was assigned to the mouseArea/touchArea of the atomNodes. I will create a new dev version to compare.

[arouinfar]

I doubt we can support both touchSnag and the swipe-to-cut, but the mechanism for cutting bonds is still open for discussion in #113. Seems like the best course of action would be to dilate the touch bounds for Hydrogen.

It looks like @Denz1994 has already increased the pointerAreas in master. However, it looks like the areas were dilated for both touch and mouse, and dilated for large atoms. Given that the atoms will be in close proximity to one another, I think it would be preferable not to dilate the pointerAreas unless need be.

@Denz1994 let's just dilate the touchArea of Hydrogen for now. The touchArea currently in master looks good to me.

[Denz1994]

Sounds good @arouinfar. I've removed the mouseArea dilation and kept the touchArea dilation. I'll close this issue since the touchArea looks good in master.

[jonathanolson]

It looks like the touch areas on atoms can be big enough where it's possible to press your finger directly over an atom and actually pick up a different one. Has this been an issue? This has been resolved in other sims by having a background that detects "misses" and searches for the closest item.

[Denz1994]

For usability purposes, this would only be concerning if this occurred in the play area. The separation threshold prevents this from happening in the play area. Atoms in the bucket are homogenous and if a user picks up the incorrect hydrogen atom that shouldn't be an issue. Thoughts @arouinfar?

[arouinfar]

For usability purposes, this would only be concerning if this occurred in the play area. The separation threshold prevents this from happening in the play area. Atoms in the bucket are homogenous and if a user picks up the incorrect hydrogen atom that shouldn't be an issue.

Agreed! I think we can close.