UI suggestion: replace "Local evaluation" checkbox with "Show evaluation" checkbox, tweak other controls

[stevage]

Motivation

In analysis mode, I basically never want "local evaluation" mode off. (If I understand this checkbox, it basically means whether to run a chess engine in the browser, which then enables local evaluation, but also playing against the computer). I don't really get why it defaults to off, every time you open analysis.

But I do sometimes want to be able to hide the evaluation, so I can practice a given position (like a mating sequence) without being told the answers. Those controls are hidden behind the hamburger icon, and annoyingly are persistent, so I have to turn them back on next time I go into analysis.

Suggestion

1. Remove the local evaluation checkbox from the main screen, and bury it under the hamburger if needed. (I assume there are some use cases where people definitely need to not have an engine running in their browser?)
2. Add a different checkbox, "Show evaluation". When enabled, show best move arrow(s), annotations, evaluation guage, and evaluation in move history. I think this is basically equivalent to the "Enable" checkbox under "Computer analysis". (The specific options can remain in the hamburger menu).
3. When entering "Practice with computer" mode, by default turn "Show evaluation" off, but allow the player to turn it back on.

[zamfofex]

This is somewhat related to this thread I opened on the forum: https://lichess.org/forum/lichess-feedback/thoughts-about-the-ux-of-the-analysis-page-and-external-engines

I spent some more time thinking about it since then, and I came up with a nice UX design that I’ve been working on implementing and submitting as a pull request. (I should be able to show what I have somewhat soon, hopefully.)

Some more thoughts, in addition to what I had said in that forum post:

• I hadn’t considered it when I opened that thread, but allowing people to see both server analysis and have local analysis complement it (by providing improved evaluation and also variation evaluations) is important, and I have considered it in my redesign.
• I think it’s important to be let people choose to disable local analysis and have it be an opt‐in, because it is computationally expensive (it certainly gets my CPU fans spinning, at least), besides requiring downloading the engine and its neural network.
• There should be a more streamlined way to control the evaluation shown. Currently, it’s completely different for server analysis vs. local analysis vs. external engine. It also should be more direct, and not hidden behind a hamburger menu.
• It should be intuitive for both new users as well as existing users. Which is to say, it should feel natural if you’ve never used the interface before, but if you already know how it currently works, it should be natural to understand the changes — I tried to avoid needlessly shifiting things around when it made sense to keep them in place.