Add coordinates of mapbox view as a derived property in plotly_relayo…

[jonmmease]

Closes#4399, following @alexcjohnson 's suggestion from #4399 (comment).

[archmoj]

@jonmmease thanks very much for the PR!
Please find my questions below:

[jonmmease]

Thanks very much for the review @archmoj and @etpinard. I believe I made the requested updates. Anything else?

[jonmmease]

Oh, I just noticed that these changes were resulting in a "unrecognized GUI edit" warning on the _derived property when resetting the plot with the modebar button. I added a check to prevent this in cf2c4fc, but let me know if you see a more elegent way to do this.

[etpinard]

Oh, I just noticed that these changes were resulting in a "unrecognized GUI edit" warning on the _derived property when resetting the plot with the modebar button

Ideally, 'mapbox._derived.coordinates[i][j] keys should never slip into the fullLayout._preGUI object. So yeah we could probably do better than your attempt in cf2c4fc.

Looks like you were successful at that on user pan and scroll-zoom: fullLayout._preGUI only contains mapbox center, zoom, bearing and pitch keys after those.

The logic for the modebar "reset" button is here:

plotly.js/src/components/modebar/buttons.js

Lines 626 to 636 in 0be6afd

	for(vari=0;i<subplotIds.length;i++){
	varid=subplotIds[i];
	varsubplotObj=fullLayout[id]._subplot;
	varviewInitial=subplotObj.viewInitial;
	varviewKeys=Object.keys(viewInitial);
	for(varj=0;j<viewKeys.length;j++){
	varkey=viewKeys[j];
	aObj[id+'.'+key]=viewInitial[key];
	}
	}

it relies on viewInitial - which does get filled with _derived in your new updateDerived mapbox subplot instance method. So I see two ways of fixing the problem,

• not stash _dervied values key-values into viewInitial (right? do we really need to stash them?)
• have the "reset" modebar button handler skip over _ keys in viewInitial

[jonmmease]

Thank for taking a look @etpinard, I went ahead and removed _derived from viewInitial since this wasn't needed after all.

[etpinard]

💃 thanks @jonmmease !!

[jonmmease]

Thanks! merging