tests/lib_2/html/canvas_test.dart

// @dart = 2.9
library CanvasTest;

import 'dart:html';

import 'package:async_helper/async_minitest.dart';

main() {
  CanvasElement canvas;
  CanvasRenderingContext2D context;
  int width = 100;
  int height = 100;

  canvas = new CanvasElement(width: width, height: height);
  document.body.append(canvas);

  context = canvas.context2D;

  test('CreateImageData', () {
    ImageData image = context.createImageData(canvas.width, canvas.height);
    List<int> data = image.data;

    expect(data.length, 40000);
    checkPixel(data, 0, [0, 0, 0, 0]);
    checkPixel(data, width * height - 1, [0, 0, 0, 0]);

    data[100] = 200;
    expect(data[100], equals(200));
  });

  test('toDataUrl', () {
    var canvas = new CanvasElement(width: 100, height: 100);
    var context = canvas.context2D;
    context.fillStyle = 'red';
    context.fill();

    var url = canvas.toDataUrl();

    var img = new ImageElement();
    img.onLoad.listen(expectAsync((_) {
      expect(img.complete, true);
    }));
    img.onError.listen((_) {
      fail('URL failed to load.');
    });
    img.src = url;
  });
}

void checkPixel(List<int> data, int offset, List<int> rgba) {
  offset *= 4;
  for (var i = 0; i < 4; ++i) {
    expect(data[offset + i], equals(rgba[i]));
  }
}