Property zerolinelayer for cartesian axes

[my-tien]

Adds a new property zerolinelayer to cartesian axes to allow drawing the zeroline above traces.

This addresses the issue that sometimes the zeroline can be barely visible:

When setting the new property yaxis.zerolinelayer = "above traces":

Disclaimer

I am required to add that…

the software is provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and noninfringement. in no event shall the authors or copyright holders be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the software or the use or other dealings in the software.

[my-tien]

@gvwilson Do you have a means to trigger the CI again? It seems that this run had a connection error on launch.

[gvwilson]

@my-tien I just re-ran CI - hope that helps.

[stephprobst]

Hi @gvwilson - Could this PR be reviewed and possibly merged soon? It seems like a reasonably sized change, that should be easy to integrate? Thank you for considering!

[emilykl]

Suggested change

	delete containerOut.zerolineLayer;
	delete containerOut.zerolinelayer;

[my-tien]

Thx for spotting! Fixed. Btw. did you just see this or is there another trick to catch this mistake?

[emilykl]

@my-tien Thank you for the contribution!

This is looking good to me -- however I've noticed that zerolinelayer doesn't seem to play nicely with the zorder property -- when a trace on a plot has zorder set, the traces are rendered above the zerolines, even if zerolinelayer is set to above traces. I've included an example below.

How big of a problem is that on your side? We are open to simply documenting the limitation but want to verify whether it will cause issues for you.

Mock:

{
    "data": [
        {
            "type": "bar",
            "x": [-1, 0, 2, 3],
            "y": [-1, 2, -3, 4],
            "name": "xy",
            "zorder": 2
        },
        {
            "line": {
                "width": 10
            },
            "mode": "lines",
            "x": [-1, 0, 2, 3],
            "y": [-3, 1, -1, 2],
            "xaxis": "x2",
            "yaxis": "y2",
            "name": "x2y2"
        }
    ],
    "layout": {
        "title": {
            "text": "Zerolines should be above traces<br>but they are rendered below"
        },
        "width": 600,
        "height": 400,
        "xaxis": {
            "showline": true,
            "zeroline": true,
            "zerolinewidth": 5,
            "zerolinecolor": "pink",
            "zerolinelayer": "above traces"
        },
        "xaxis2": {
            "showline": true,
            "overlaying": "x",
            "zeroline": true,
            "zerolinewidth": 5,
            "zerolinecolor": "pink",
            "zerolinelayer": "above traces",
            "side": "top"
        },
        "yaxis": {
            "showline": true,
            "zeroline": true,
            "zerolinewidth": 5,
            "zerolinecolor": "black",
            "zerolinelayer": "above traces",
            "range": [-1, 4]
        },
        "yaxis2": {
            "showline": true,
            "zeroline": true,
            "zerolinewidth": 5,
            "zerolinecolor": "black",
            "zerolinelayer": "above traces",
            "range": [-3, 2],
            "overlaying": "y",
            "side": "right"
        }
    }
}

Image:

[my-tien]

Hi Emily, thanks for the heads up.

I didn't dig into the zorder logic much, but I assume to make it work with it, the zeroline drawing would have to be moved to another location? So it sounds like it could become a major change (correct me if I'm wrong).

In any case, from our side it's okay to document the limitation. – I've added a note to the description of the property.