Canvas.drawShadow requires DPR to calculate shadow length, and currently it gets the DPR implicitly from the first window:

// lib/ui/painting/canvas.cc
  SkScalar dpr = static_cast<float>(UIDartState::Current()
                                        ->platform_configuration()
                                        ->get_window(0)
                                        ->viewport_metrics()
                                        .device_pixel_ratio);

This is not compatible with multi-view, because in multi-view there might not be a window 0 if the platform disables implicit view. This DPR should come from the target view of this drawing command.

However, the drawShadow signature does not allow inserting a view ID or DPR anywhere. There's an elevation parameter, but it's a pre-DPR length.

  void drawShadow(Path path, Color color, double elevation, bool transparentOccluder);

To solve this in a non-breaking way, we can either

• create a new drawShadowWithDpr that has an additional parameter float dpr, or
• create a new drawShadowOnView that has an additional parameter int viewId.

Either way, we'll need to deprecate drawShadow afterwards.