在滑动 Flutter 时应用颜色滤镜图片

Question

我的目标是像这样在背景图像上方水平滑动颜色过滤器：

我正在使用多个矩阵来创建一些颜色过滤器，并且我知道我必须用 ColorFiltered 包装图像才能应用过滤器：这没有问题。

然后，当我尝试滑动这些过滤器时，我不知道如何应用它们。 这是演示的代码：

class PageFilters extends StatefulWidget {

  double ratio;
  String file;

  PageFilters({required this.ratio,required this.file});

  @override
  _PageFiltersState createState() => _PageFiltersState();
}

class _PageFiltersState extends State<PageFilters> {

  FilterList filters = FilterList();


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Stack(
        alignment: Alignment.center,
        children: [
          Image.file(File(widget.file),fit: BoxFit.cover),
          PageView.builder(
            physics: const ClampingScrollPhysics(),
            itemCount: filters.list.length,
              itemBuilder: (context,index) {
            return Center(
              child: ColorFiltered(
                colorFilter: ColorFilter.matrix(filters.list[index].matrix),
                child: Container(
                  color: index == 0 ? Colors.transparent : Colors.white.withOpacity(0.1),
                  alignment: Alignment.center,
                  height: Constants.maxWidth*widget.ratio,
                ),
              ),
            );
          }),
        ],
      ),
    );
  }
}

在滑动过程中过滤器是否直接应用于图像并不重要，只要过滤器可见，我可以检索它并稍后应用它。

感谢任何线索或解决方案

Answer 1

这个想法是将图像移动到与页面移动相反的方向 - 所以如果PageView 正在将孩子（ColorFiltered 小部件）移动到右侧，您必须将大孩子（Image 小部件）移动到左边，所以它保持在同一个地方 - 虽然理论上很简单，但实际上它可能会让人头疼 - 幸运的是有 CustomSingleChildLayout 小部件可以为我们节省大量工作：

class ColorFilteredPageView extends StatefulWidget {
  final ImageProvider image;
  final List<ColorFilter> filters;
  final List<String> filterNames;

  ColorFilteredPageView({
    @required this.image,
    @required this.filters,
    @required this.filterNames,
  }) : assert(filters.length == filterNames.length);

  @override
  _ColorFilteredPageViewState createState() => _ColorFilteredPageViewState();
}

class _ColorFilteredPageViewState extends State<ColorFilteredPageView> {
  PageController controller = PageController();

  @override
  Widget build(BuildContext context) {
    return PageView.builder(
      controller: controller,
      itemCount: widget.filters.length,
      itemBuilder: (ctx, index) {
        return Stack(
          fit: StackFit.expand,
          children: [
            ClipRect(
              child: ColorFiltered(
                colorFilter: widget.filters[index],
                child: CustomSingleChildLayout(
                  delegate: _ColorFilteredPageViewDelegate(index, controller),
                  child: Image(image: widget.image, fit: BoxFit.cover),
                ),
              ),
            ),
            ...outlinedName(widget.filterNames[index]),
          ],
        );
      },
    );
  }
}

/*
// NOTE
// AnimatedBuilder + FractionalTranslation can also be used
// instead of CustomSingleChildLayout but it is kind of workaround imho....
    ClipRect(
      child: ColorFiltered(
        colorFilter: widget.filters[index],
        child: AnimatedBuilder(
          animation: controller,
          builder: (context, child) {
            return FractionalTranslation(
              translation: controller.position.haveDimensions?
                Offset(controller.page - index, 0) : Offset.zero,
              child: child,
            );
          },
          child: Image(image: widget.image, fit: BoxFit.cover),
        ),
      ),
    ),
*/

class _ColorFilteredPageViewDelegate extends SingleChildLayoutDelegate {
  final int index;
  final PageController controller;

  _ColorFilteredPageViewDelegate(this.index, this.controller) : super(relayout: controller);

  Offset getPositionForChild(Size size, Size childSize) {
    // print('index: $index, dx: ${controller.offset - index * size.width}');
    return Offset(controller.offset - index * size.width, 0);
  }

  @override
  bool shouldRelayout(covariant SingleChildLayoutDelegate oldDelegate) => false;
}

Iterable<Widget> outlinedName(String name) {
  final styles = [
    TextStyle(
      foreground: Paint()
        ..color = Colors.black
        ..style = PaintingStyle.stroke
        ..strokeWidth = 4
        ..maskFilter = MaskFilter.blur(BlurStyle.solid, 2),
      fontWeight: FontWeight.w500,
    ),
    TextStyle(
      color: Colors.white,
      fontWeight: FontWeight.w500,
    ),
  ];
  return styles.map((style) => Align(
    alignment: Alignment(0, 0.75),
    child: Text(name,
      textScaleFactor: 2.5,
      textAlign: TextAlign.center,
      style: style,
    ),
  ),);
}

现在有一些示例过滤器：

final myFilters = [
  ColorFilter.mode(Colors.transparent, BlendMode.dst),
  ColorFilter.mode(Colors.teal, BlendMode.softLight),
  ColorFilter.mode(Colors.teal, BlendMode.hardLight),
  ColorFilter.mode(Colors.deepPurple, BlendMode.hue),
  // sepia
  ColorFilter.matrix([
    0.393, 0.769, 0.189, 0, 0,
    0.349, 0.686, 0.168, 0, 0,
    0.272, 0.534, 0.131, 0, 0,
    0,     0,     0,     1, 0,
  ]),
  // greyscale
  ColorFilter.matrix([
    0.2126, 0.7152, 0.0722, 0, 0,
    0.2126, 0.7152, 0.0722, 0, 0,
    0.2126, 0.7152, 0.0722, 0, 0,
    0,      0,      0,      1, 0,
  ]),
  // invert
  ColorFilter.matrix([
    -1,  0,  0, 0, 255,
    0,  -1,  0, 0, 255,
    0,   0, -1, 0, 255,
    0,   0,  0, 1,   0,
  ]),
  ColorFilter.linearToSrgbGamma(),
  ColorFilter.srgbToLinearGamma(),
  ColorFilter.mode(Colors.transparent, BlendMode.dst),
];

final myFilterNames = [
  'original image', 'teal soft light', 'teal hard light', 'deep purple hue', 'matrix sepia', 'matrix greyscale', 'matrix invert', 'linearToSrgbGamma', 'srgbToLinearGamma', 'original image again',
];

你可以按如下方式使用它：

child: ColorFilteredPageView(
  image: NetworkImage('https://unsplash.com/photos/3fEzry0pIms/download?force=true&w=640'),
  filters: myFilters,
  filterNames: myFilterNames,
),

Answer 2

最简单的方法是使用 RenderRepaintBoundary 来截屏：

static GlobalKey _screenCapture = new GlobalKey();

  Uint8List _takeScreenShot() async {
    RenderRepaintBoundary boundary = _screenCapture.currentContext.findRenderObject();
    ui.Image image = await boundary.toImage(pixelRatio: 2.0);
    ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);
    Uint8List pngBytes = byteData.buffer.asUint8List();
    return pngBytes;
  }

      body: Stack(
        key: _screenCapture,
        alignment: Alignment.center,
        children: [
          Image.file(File(widget.file),fit: BoxFit.cover),
          PageView.builder(
            physics: const ClampingScrollPhysics(),
            itemCount: filters.list.length,
              itemBuilder: (context,index) {
            return Center(
              child: ColorFiltered(
                colorFilter: ColorFilter.matrix(filters.list[index].matrix),
                child: Container(
                  color: index == 0 ? Colors.transparent : Colors.white.withOpacity(0.1),
                  alignment: Alignment.center,
                  height: Constants.maxWidth*widget.ratio,
                ),
              ),
            );
          }),
        ],
      ),