DonutChart diagram type

[ibirothe]

Lots of the logic can be borrower from PieChart. Relevant infographic shapes are already included. Might need some additional styling parameters.

Example:

[johnjehiel]

Hi @ibirothe
I would like to work on this issue. Could you please assign it to me ?

[ibirothe]

@johnjehiel Let's go! Feel free to join the Discord Server in the readme if you got any questions about the codebase.

[ibirothe]

If you look right here, there you need to add the arc object:

https://github.com/MerrimanInd/drawpyo/blob/main/src/drawpyo/diagram/extended_objects.py

The shape itself is already imported to the infographics library toml:

https://github.com/MerrimanInd/drawpyo/blob/main/src/drawpyo/shape_libraries/infographics.toml

There is another similar object in the draw.io-infographics library. You might check it out in the reference diagrams to see if it's a better fit.

[johnjehiel]

Thanks for the references, very helpful !

I looked into the draw.io infographics library and found that mxgraph.basic.partConcEllipse looks like a better fit than arc. Unlike arc, it exposes an Arc Width parameter, which allows proper control over ring thickness.

I've planned to add this shape to infographics.toml and introduce a DonutArc object for DonutChart diagram type.

[ibirothe]

Perfect, that's exactly the better shape I thought off. Have fun hacking!

[johnjehiel]

I also wanted to get your thoughts on label positioning for donut charts and potentially pie charts.

To give users better control, I was thinking of the following options:

Numbers / values

• Always rendered inside the slice / arc

Labels for those values are placed in one of the following locations:

• Inside the inner circle, near the corresponding arc (this kinda looks weird with all the labels cluttered in the middle)
• Along with the number/value inside the arc itself (default, similar to current pie chart implementation)
• Outside the outer circle, near the corresponding arc

Optional

• Leader lines for labels placed outside the chart

I believe some of these ideas could also apply to pie charts, so label positioning and leader lines could potentially be tracked as a separate issue, independent of the initial donut chart implementation.

I got this idea after looking at a few reference diagrams.
https://www.datylon.com/resources/chart-library/donut-chart
https://www.datylon.com/resources/chart-library/pie-chart

[ibirothe]

Label position is a difficult topic indeed. So PieChart currently positions the label on a line between center and the middle of a segment. If we turn the label offset from a CONSTANT into a kwarg, users could easily move the label out of the circle itself.

The text of a label can be set dynamically using the label_formatter kwarg and passing a callable. So it's up
to the user what they want to write. The default is a float between 0 and 1.

I am working on a legend that users can use to map colors. This could be an easy way to provide additional information about the segments, without overloading them.

If we want to add a line between segment and label, that should be fairly easy. We can pass the setting as a kwarg, defaulting to false. If set, we just need a couple conditional lines.

[ibirothe]

Additionally feel free to apply the same way of label positioning to PieChart for consistency, if you want.