D1155: FillOpacityMask Requires Aliased Rendering
FillOpacityMask requires that the antialias mode be set to D2D1_ANTIALIAS_MODE_ALIASED.
When an application calls ID2D1RenderTarget::FillOpacityMask, the antialias mode of the rendertarget involved should be D2D1_ANTIALIAS_MODE_ALIASED. A render target’s default behavior is to use antialiasing, so it is necessary to call ID2D1RenderTarget::SetAntialiasMode before filling an opacity mask.
Use ID2D1RenderTarget::SetAntialiasMode to ensure a rendertarget uses aliased rendering while filling an opacity mask. If subsequent operations require antialiasing, set the target’s antialias mode back to D2D1_ANTIALIAS_MODE_PER_PRIMITIVE. Ensure that the calls to ID2D1RenderTarget::SetAntialiasMode and ID2D1RenderTarget::FillOpacityMask are issued on the same target.