Allows you extract an image of specific widgets within your app. Includes the ability to ignore certain widgets and to crop the final image.

screenshot.dart

import 'dart:typed_data';
import 'dart:ui' as ui;

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

// Note: [ui.Image] represents the lower level image data while [Image] represents a renderable image.

/// Provides the ability to take screenshots of specific widgets.
mixin Screenshot<T extends StatefulWidget> on State<T> {
  static GlobalKey _key = new GlobalKey();

  /// Wrap this around widget you wish to screenshot.
  Widget screenshotThis(Widget child) => RepaintBoundary(key: _key, child: child);

  /// Returns the screenshot of the widgets wrapped with [screenshotThis].
  /// Applies an optional background and crop to the final image.
  Future<ScreenshotData> takeScreenshot({Color background, Rect crop}) async {
    var imageDataRaw = await _getScreenshotData();
    var imageData = await _updateImage(imageDataRaw, background, crop);
    return _convertDataToImage(imageData);
  }

  /// Returns the raw image of the widgets to screenshot.
  Future<ui.Image> _getScreenshotData() async {
    RenderRepaintBoundary boundary = _key.currentContext.findRenderObject();
    return boundary.toImage();
  }

  /// Converts the raw image into a renderable form.
  Future<ScreenshotData> _convertDataToImage(ui.Image imageData) async {
    var byteData = await imageData.toByteData(format: ui.ImageByteFormat.png);
    var pngBytes = byteData.buffer.asUint8List();
    var image = Image.memory(pngBytes);
    return ScreenshotData(image, pngBytes);
  }

  /// Processes an image with an optional background color and crop
  Future<ui.Image> _updateImage(ui.Image image, [Color background, Rect crop]) {
    var pictureRecorder = new ui.PictureRecorder();
    Canvas canvas = new Canvas(pictureRecorder);
    canvas.drawPaint(Paint()..color = background ?? Colors.transparent);

    // No crop provided so render the full image
    if (crop == null) {
      int width = image.width, height = image.height;
      canvas.drawImage(image, Offset.zero, Paint());
      return pictureRecorder.endRecording().toImage(width, height);
    }

    // Crop the image by extracting the crop rect and moving to the top left
    final width = crop.width, height = crop.height;
    var dest = Rect.fromLTWH(0, 0, width, height);
    canvas.drawImageRect(image, crop, dest, Paint());
    return pictureRecorder.endRecording().toImage(width.floor(), height.floor());
  }
}

/// Contains a renderable Image and the raw image bytes.
class ScreenshotData {
  final Image image;
  final Uint8List pngBytes;
  ScreenshotData(this.image, this.pngBytes);
}