Refactor dashed line code to use the new Path APIs

[Hixie]

charts/charts_flutter/lib/src/canvas/line_painter.dart

Line 81 in 2f1ad24

/// Draws dashed lines lines between each point.

We can probably do better (for dashed lines) now that we expose the path measuring API.

[mit-mit]

cc @cbbraun

[cbbraun]

Hixie, Can you point us to details or APIs?

[Hixie]

We had to revert it unfortunately, but it'll eventually be flutter/engine#4957.

[Hixie]

Ok, it's landed. Given a Path that you want to dash, you can call computeMetrics on that Path, iterate over the returned list of PathMetric objects, and for each PathMetric object, use extractPath to grab all the Path for each dash. You can then add all those subpaths to a single Path use addPath, and draw the whole thing use drawPath.

[dnfield]

I have an implementation here: https://github.com/dnfield/flutter_path_drawing/blob/master/lib/src/dash_path.dart

Available on pub https://pub.dartlang.org/packages/path_drawing