Pie Chart, how to add a gap between each section?

[lsaudon]

I'd like there to be spaces between each value.

I try with size in IntervalMark but nothing change

Actual	Expected

[entronad]

To create a gap between the sections of a pie chart using the Flutter graphic library, you need to employ a workaround by styling the border of each pie slice. The library, at present, does not offer a direct gap or spacing property for its pie chart implementation.

The solution involves using the style property of the IntervalElement. By setting the strokeWidth to a desired gap size and the strokeColor to the chart's background color, you can effectively create the illusion of a space between each section.

Implementation

Here is a code example demonstrating how to add a 2-pixel white gap between the sections of a pie chart:

import 'package:flutter/material.dart';
import 'package:graphic/graphic.dart';

class PieChartWithGaps extends StatelessWidget {
  final List<Map<String, dynamic>> data = [
    {'category': 'A', 'value': 20},
    {'category': 'B', 'value': 30},
    {'category': 'C', 'value': 40},
    {'category': 'D', 'value': 10},
  ];

  @override
  Widget build(BuildContext context) {
    return Chart(
      data: data,
      variables: {
        'category': Variable(
          accessor: (Map map) => map['category'] as String,
        ),
        'value': Variable(
          accessor: (Map map) => map['value'] as num,
        ),
      },
      transforms: [
        Proportion(
          variable: 'value',
          as: 'percent',
        ),
      ],
      coord: PolarCoord(
        transposed: true,
        dimCount: 1,
      ),
      elements: [
        IntervalElement(
          variable: 'percent',
          color: ColorAttr(
            variable: 'category',
            values: [
              Colors.blue,
              Colors.green,
              Colors.orange,
              Colors.red,
            ],
          ),
          // Add a border to simulate a gap
          style: PaintStyle(
            strokeColor: Colors.white, // Color of the gap (usually background)
            strokeWidth: 2,           // Width of the gap
          ),
        ),
      ],
    );
  }
}

Key Concepts

• IntervalElement: In the graphic library, a pie chart is fundamentally an IntervalElement in a PolarCoord (polar coordinate system).
• style Property: This property of the IntervalElement allows you to customize the painting style of the chart elements. It accepts a PaintStyle object.
• PaintStyle: This is where you define visual properties like strokeColor and strokeWidth.
  • strokeColor: Set this to the color of your chart's background to create the appearance of an empty space.
  • strokeWidth: This determines the thickness of the "gap".

By applying a stroke to each pie section that matches the background, you create a visual separation, achieving the desired gap effect in a clean and efficient manner.

This solution was generated by an AI. I would appreciate any feedback on whether it effectively solved your problem!

For more detailed information, you can always refer to the official Graphic documentation. Good luck with your project!