Checking "H3O+/OH- Ratio" checkbox takes ~1 second

[ghost]

Test Device

Hopper, Leibniz

Operating System

iOS 12.3.1

Browser

Mobile Safari 12

Problem Description

For phetsims/qa#323. In the "Micro" and "My Solutions" screens, if you have lots of ions of either kind, i.e. the solution is either highly acidic or highly basic, and you check the hydronium / hydroxide ratio checkbox, it takes about one second for the ions to appear.

Visuals

It doesn't look that bad in this gif, but it is noticeable when you're playing with the sim.

[pixelzoom]

Thanks for reporting.

The time it takes to display the image depends on the number of molecules; more molecules requires more time. And the implementation is unchanged from the published version. That said...

I tested on both ends of the iPad spectrum (iPad6 + iOS12, iPad2 + iOS9) and performance seems acceptable. @arouinfar please confirm. If it's not acceptable, I'll investigate whether there's a more efficient way to draw the molecules.

[arouinfar]

@lmulhall-phet observed this issue on some of our newest iPads, Hopper (iPad 6, iOS 12) and Leibniz (iPad Air 2, iOS 12). Testing myself, I would say that the lag is borderline acceptable. The lag is long enough that some users may end up tapping the checkbox a 2nd time while waiting for the particles to appear, thereby unchecking the checkbox. While annoying, this issue isn't particularly harmful.

Interestingly, latest (1.2.18) is buttery smooth, and there is absolutely no noticeable lag. Perhaps the 1.3 branch has picked up some common code changes which significantly slow things down. I think a short investigation might be worthwhile @pixelzoom.

[pixelzoom]

Rendering of H₃O⁺/OH^- Ratio is performed in RatioNode. This issue and #83 are identical, because RatioNode is not updated until it becomes visible. So checking the checkbox is equivalent to selecting a new solute, or changing a solution's pH. I'm going to close this issue as "duplicate", and continue work in #83.