Linked Axes

[epezent]

I'm considering an axis linking system so that drag on one plot will cause another plot to drag (see #53 (comment) and #94 (comment)). It is currently possible by exploiting GetPlotLimits and SetNextPlotLimts, but setting up a bidirectional system is more difficult.

Implementation details aside, what do folks think of something like this:

double xmin, xmax, ymin, ymax;

ImPlot::LinkNextAxes(&xmin,&xmax,&ymin,&ymax);
if (ImPlot::BeginPlot("Plot A")) { 
    ...
    ImPlot::EndPlot(); 
}

ImPlot::LinkNextAxes(&xmin,&xmax,&ymin,&ymax);
if (ImPlot::BeginPlot("Plot B")) { 
    ...
    ImPlot::EndPlot(); 
}

The pointer values will be used to set the next plot limits, and if any drag input is taken, it will update them accordingly so the changes can propagate to other plots. NULL could be passed for axes not linked. I haven't thought it out completely, but this is the most flexible and elegant solution I can come up with for now.

@PeterJohnson, @ozlb ...thoughts?

[PeterJohnson]

I like it.

[hoffstadt]

I also like this idea. That would certainly be a unique and useful feature.

[Prinkesh]

I implemented this by wrapping BeginPlot() .. EndPlot()calls under new method BeginSubPlot()...EndSubPlot() . where subplot method hold the shared axis states of all children plots and all the child plot uses pointer to the parent axis state instead of a local copy . If there is no subplot parent for a plot then a local axis state is created for the plot .

One can define in the BeginSubPlot call what axis is to be shared .

So to share X axis one can write in this manner

if (ImPlot::BeginSubPlot("X Shared", ImSubPlot_ShareAxisX)) {
   if (ImPlot::BeginPlot("Plot A")) { 
    ...
    ImPlot::EndPlot(); 
   }

   if (ImPlot::BeginPlot("Plot B")) { 
    ...
    ImPlot::EndPlot(); 
   }
   ImPlot::EndSubPlot();
}
 

[PeterJohnson]

I like how generic the original proposed solution is, e.g. I can have linked plots in separate windows, or separated by non-linked plots.

[ozlb]

I like @epezent solution; in my applications I will probably “link” always x-axis and never y-axis (do you need up to 3 of ymin/ymax !?)

I don’t like the name “link”, i will use synchronized or “sync” but this is definitely not a big deal for me.

[epezent]

I have this working in the linked-axes branch if anyone wants to give it a try. I'll merge later today after more testing.

I like this system because:

1. you can link any number of plots/axes
2. they don't have to be the same axis between plots (e.g. link an X to a Y if you please)
3. it can be used for other purposes such as externally controlled axis limits

[ozlb]

Great!
What happens when while dragging the other plot Is hovered?

[epezent]

You mean like this? Nothing, as would be expected.

[ozlb]

Great! It behaves like this because the drag operation is passing from one plot to the next or because it’s kept active in plot where it starts?

[epezent]

The latter

[ozlb]

The latter

I was wondering to close PR #98 but not yet ...

[epezent]

Merged!