如何从使用 CustomPainter 绘制的 canvas 中获取图像？

Question

在我的 Flutter 应用程序中，我使用 CustomPainter 允许用户在屏幕上绘制他们的签名。我需要找到一种方法将其另存为图像。

PictureRecorder works nicely when you are able to pass the PictureRecorder object to the canvas as per :

final recorder = new PictureRecorder();
Canvas(recorder).drawSomething;
final picture = recorder.endRecording();

然而，当使用 CustomPainter 时，canvas 是 Paint() 函数的参数。

class myPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    drawToCanvas(canvas);

  @override
  bool shouldRepaint(CustomPainter old) {
    return false; 
}

总而言之：

如何从 CustomPainter 生成图像？
如果答案是使用 PictureRecorder，我如何将记录器传递给 canvas?

Answer 1

您不需要在 CustomPainter paint 方法中将 PictureRecorder 传递给 canvas。相反，您可以使用具有图片记录器的不同 canvas 直接调用绘画。例如：

Future<Image> getImage() async {
final PictureRecorder recorder = PictureRecorder();
myPainter.paint(Canvas(recorder), mySize);
final Picture picture = recorder.endRecording();

return await picture.toImage(width, height);
}

如何从使用 CustomPainter 绘制的 canvas 中获取图像？

How to get an image from a canvas drawn with CustomPainter?

canvas

image

custom-painting

dart

flutter