Background: why develop this component? At present, video synthesis technology is used in our flitter app, which involves the clipping of video or picture materials. At present, the common components in the market are based on pictures, and basically use canvas for rendering and clipping, which does not meet our business needs, so we need to develop a clipping component ourselves.



Demand analysis

At the beginning of requirement design, considering the habit of gesture and referring to most editing tools, the following requirements are defined:

  • The clipping Box is fixed in a position on the screen. The position and size of the material can be adjusted by dragging with one finger and zooming with two fingers to frame the clipping range

  • The minimum edge of the material cannot be less than the corresponding edge of the clipping box, that is, the clipping Box can only move relatively within the range of the material

  • The types of supporting materials include pictures and videos


cropRectRectIf you do not fill in the initial clipping region, it will be filled and centered by default, which is similar to cover-
clipSizeSizeSize of material to be cutRequired
cropRatioSizeCrop box scale, default16:9Size(16, 9)
childWidgetMaterial to be cutRequired
maxCropSizeSizeThe maximum width and height of the current scale of the clipping box is mainly used when the size of the clipping box needs to be adjusted actively. If there is no special requirement, it does not need to be configuredCalculate based on parent component
maxScaleDoubleMaximum size allowed to enlarge10.0
needInnerBorderboolWhether the inner border decoration is required in the square mode (if there are rounded corners, it will not be displayed)false
cropBoxTypeCropBoxTypeCrop box style, default square, can be changed to circle. If it is a circle, the value set by CropRatio will be invalid and forced to 1:1CropBoxType.Square
gridLineGridLineClipping gridlines-
backgroundColorColorBackground ColorColor(0xff141414)
cropBoxBorderCropBoxBorderCrop box style, including color, width and rounded corner informationcropBoxBorder.width = 2 cropBoxBorder.color = Colors.white cropBoxBorder.radius = Radius.circular(0)
cropRectUpdateStartFunctionCallback when crop region begins to change-
cropRectUpdateFunction(Rect rect)Callback when clipping region changes-
cropRectUpdateEndFunction(Rect rect)Callback when clipping region endRequired

Demo code

Can see example in github



  crop_box: ^0.1.5


import 'package:crop_box/crop_box.dart';

// ...

  // cropRect: Rect.fromLTRB(1 - 0.4083, 0.162, 1, 0.3078), // 2.4倍 随机位置
  // cropRect: Rect.fromLTRB(0, 0, 0.4083, 0.1457), //2.4倍,都是0,0
  cropRect: Rect.fromLTRB(0, 0, 1, 0.3572), // 1倍
  clipSize: Size(200, 315),
  cropRatio: Size(16, 9),
  cropRectUpdateEnd: (rect) {
    print("rect final $rect");
  cropRectUpdate: (rect) {
    print("rect change $rect");
    width: double.infinity,
    height: double.infinity,
    fit: BoxFit.cover,
    loadingBuilder: (BuildContext context, Widget child, ImageChunkEvent loadingProgress) {
      if (loadingProgress == null)
        return child;
      return Center(
        child: CircularProgressIndicator(
          value: loadingProgress.expectedTotalBytes != null
              ? loadingProgress.cumulativeBytesLoaded / loadingProgress.expectedTotalBytes
              : null,

Real Image Crop

You can Use ImageCrop.getResult to get real image bytes.

more details in example

/// get origin image uint8List
Uint8List bytes = (await NetworkAssetBundle(Uri.parse(imageUrl))
/// get result uint8List
Uint8List result = await ImageCrop.getResult(
  clipRect: _resultRect, 
  image: bytes


  • x Dynamically transform crop box scale

  • x Support circle clipping box drawing

  • Optimize boundary calculation code

  • x Support the drawing of fillet clipping box

  • Support rotation

  • x Support Gridlines

  • x Real image crop to Uint8List