c# - Possible to have anti-aliasing when drawing a clipped image?

Question

Currently, I'm successfully using the Graphics class to draw a non-rectangular clipped image (the turtle inside):

My code looks something like:

using (var g = Graphics.FromImage(image))
{
    g.InterpolationMode = InterpolationMode.HighQualityBicubic;

    using (var gfxPath = new GraphicsPath())
    {
        gfxPath.AddEllipse(r);

        using (var region = new Region(r))
        {
            region.Exclude(gfxPath);

            g.ExcludeClip(region);

            g.DrawImage(turtleImage, r, r2, GraphicsUnit.Pixel);
        }
    }
}

This all works just as expected. What I do not know how to solve is to make the image border anti-aliased.

The image zoomed looks like:

I.e. the border where the image ends and the transparent "background" of the image starts is a rough cut, not a smooth alpha blending.

My question is:

Is it possible to clip a drawn image and having anti-aliasing active?

Answer 1

If you want to go for full blown feathering you should consider taking a look at this article:

http://danbystrom.se/2008/08/24/soft-edged-images-in-gdi/

If you want a quick and easy solution you could probably draw the image first then draw a GraphicsPath on top of it using a solid white brush with antialiasing. You would do something like this:

Rectangle outerRect = ClientRectangle;
Rectangle rect = Rectangle.Inflate(outerRect, -20, -20);

using (Image img = new Bitmap("test.jpg"))
{
    g.DrawImage(img, outerRect);

    using (SolidBrush brush = new SolidBrush(Color.White))
    using (GraphicsPath path = new GraphicsPath())
    {
        g.SmoothingMode = SmoothingMode.AntiAlias;

        path.AddEllipse(rect);
        path.AddRectangle(outerRect);

        g.FillPath(brush, path);
    }
}