D1185: FillGeometry Opacity Mask Brush Restriction
If FillGeometry is used with an opacity mask, the primary brush must be a clamped bitmap brush.
When using ID2D1RenderTarget::FillGeometry, the primary brush was a type other than ID2D1BitmapBrush. Or, the primary brush had an x- or y- extend mode other than D2D1_EXTEND_MODE_CLAMP.
If the application uses FillGeometry with an opacity mask, ensure that the primary brush (not to be confused with the opacity brush) is an ID2D1BitmapBrush with clamped extend modes. If opacity masking behavior is not important, leave the opacity brush argument as NULL to remove these restrictions on the primary brush.