Flutter canvas 绘制不同 colored颜色 的原始点

你能试试这个吗？

void _paintPoints(Canvas canvas, List matrix, Size size) {
  final width = size.width / matrix.length;
  final height = size.height / matrix.first.length;

  final Map<Color, Set<Offset>> map = HashMap();

  for (var i = 0; i < matrix.length; i++) {
    for (var j = 0; j < matrix[i].length; j++) {
      final offset = Offset(i * width, j * height);
      final color = Color.fromARGB(
          matrix[i][j][3], matrix[i][j][0], matrix[i][j][1], matrix[i][j][2]);
      map.putIfAbsent(color, () => HashSet()).add(offset);
    }
  }

  for (var e in map.entries) {
    canvas.drawRawPoints(
      PointMode.points,
      Float32List.fromList(e.value.expand((e) => [e.dx, e.dy]).toList()),
      paint
        ..color = e.key
        ..blendMode = BlendMode.srcOver
        ..strokeWidth = 2.0,
    );
  }
}

很抱歉，我不得不把它作为回复贴出来.这是一个试用代码.我建议缓存映射结果，并使用即将到来的矩阵和大小的比较来计算新的映射值.

编辑: 我做了一些编辑，它应该运行得很快.这里的 idea 是最大限度地减少内存地址计算.

更新的代码

void _paintPoints(Canvas canvas, List matrix, Size size) {
  final r = matrix.length;
  final c = matrix.first.length;
  final width = size.width / r;
  final height = size.height / c;

  final Map<Color, Set<Offset>> map = HashMap();

  for (var i = 0; i < r; i++) {
    final row = matrix[i];
    for (var j = 0; j < c; j++) {
      final cell = row[j];
      final offset = Offset(i * width, j * height);
      final color = Color.fromARGB(cell[3], cell[0], cell[1], cell[2]);
      map.putIfAbsent(color, () => HashSet()).add(offset);
    }
  }

  for (var e in map.entries) {
    canvas.drawPoints(
      PointMode.points,
      e.value.toList(),
      paint
        ..color = e.key
        ..blendMode = BlendMode.srcOver
        ..strokeWidth = 2.0,
    );
  }
}

现在 map 的创建速度应该要快得多.我自己做了一些基准测试，发现用i和j访问3D列表比引用它要花更多的时间.此外，还将行点更改为点.你可以把它改回来.