update 通过CSS来设置全屏效果，以解决页面存在tabBar时，组件偏下的问题。并做了h5端的适配。

src/components/taro-cropper/index.scss

@@ -0,0 +1,25 @@
+.canvas-item {
+  background: rgba(0,0,0,0.8);
+  position: relative;
+}
+.canvas-fullscreen {
+  width: 100%;
+  height: 100%;
+}
+.cut-canvas-item {
+  position: absolute;
+}
+.taro-cropper {
+  position: relative;
+}
+.taro-cropper-fullscreen {
+  position: fixed;
+  left: 0;
+  top: 0;
+  width: 100%;
+  height: 100%;
+}
+html .taro-tabbar__container .taro-cropper-fullscreen {
+  height: calc(100% - 100rpx);
+}
+

src/components/taro-cropper/index.tsx

@@ -46,6 +46,7 @@ class TaroCropperComponent extends Taro.PureComponent<TaroCropperComponentProps,
     themeColor: '#00ff00',
     maxScale: 3,
     fullScreen: false,
+    fullScreenCss: false,
     hideFinishText: false,
     hideCancelText: true,
     finishText: '完成',
@@ -489,6 +490,7 @@ class TaroCropperComponent extends Taro.PureComponent<TaroCropperComponentProps,
       height,
       cropperCanvasId,
       fullScreen,
+      fullScreenCss,
       themeColor,
       hideFinishText,
       cropperWidth,
@@ -504,6 +506,11 @@ class TaroCropperComponent extends Taro.PureComponent<TaroCropperComponentProps,
     const _height = fullScreen ? this.systemInfo.windowHeight : this._getRealPx(height);
     const _cropperWidth = this._getRealPx(cropperWidth);
     const _cropperHeight = this._getRealPx(cropperHeight);
+    const isFullScreenCss = fullScreen && fullScreenCss
+
+    const croperStyle = isFullScreenCss ? {} : {
+      position: 'relative'
+    }
 
     const canvasStyle: CSSProperties = {
       background: 'rgba(0, 0, 0, 0.8)',
@@ -577,12 +584,11 @@ class TaroCropperComponent extends Taro.PureComponent<TaroCropperComponentProps,
       </CoverView>
     }
     return (
-      <View style={{
-        position: 'relative'
-      }}>
+      <View className={`taro-cropper ${isFullScreenCss ? 'taro-cropper-fullscreen' : ''}`} style={croperStyle}>
         <Canvas
           canvasId={cropperCutCanvasId}
           style={cutCanvasStyle}
+          className={`cut-canvas-item ${isFullScreenCss ? 'cut-canvas-fullscreen' : ''}`}
 
         />
         <Canvas
@@ -591,6 +597,7 @@ class TaroCropperComponent extends Taro.PureComponent<TaroCropperComponentProps,
           onTouchEnd={this.handleOnTouchEnd}
           canvasId={cropperCanvasId}
           style={canvasStyle}
+          className={`canvas-item ${isFullScreenCss ? 'canvas-fullscreen' : ''}`}
           disableScroll
         >
         </Canvas>