anchor.diff:  
     @override
     ui.EngineLayer addToScene(ui.SceneBuilder builder, [ Offset layerOffset = Offset.zero ]) {
  -    builder.pushShaderMask(shader, maskRect.shift(layerOffset), blendMode);
  +    final Rect shiftedMaskRect = layerOffset == Offset.zero ? maskRect : maskRect.shift(layerOffset);
  +    builder.pushShaderMask(shader, shiftedMaskRect, blendMode);
       addChildrenToScene(builder, layerOffset);
       builder.pop();
       return null; // this does not return an engine layer yet.
  
positive.code: 
    @override
    ui.EngineLayer addToScene(ui.SceneBuilder builder, [ Offset layerOffset = Offset.zero ]) {
      final Rect shiftedRect = rect.shift(layerOffset);
      builder.addTexture(
        textureId,
        offset: shiftedRect.topLeft,
  
negative.code:       enabled = !debugDisableClipLayers;
        return true;
      }());
      if (enabled) {
        final RRect shiftedClipRRect = layerOffset == Offset.zero ? clipRRect : clipRRect.shift(layerOffset);
        builder.pushClipRRect(shiftedClipRRect, clipBehavior: clipBehavior);
      }
      addChildrenToScene(builder, layerOffset);
      if (enabled)
        builder.pop();
  