Question

The following code will draw an ellipse on an image and fill that ellipse with the Tomato colour

string imageWithTransEllipsePathToSaveTo = "~/Images/imageTest.png";
Graphics g = Graphics.FromImage(sourceImage);

g.FillEllipse(Brushes.Tomato, 50, 50, 200, 200);

sourceImage.Save(Server.MapPath(imageWithTransEllipsePathToSaveTo), ImageFormat.Png);

If I change the brush to Transparent it obviously will not show because the ellipse will be transparent and the image underneath will show.

How do I set the ‘background’ of the ellipse to be transparent so that the image contains a transparent spot?

EDIT:

Sorry for the confusion but like this…

Answer 1

This is my second answer and works with an Image instead of a color brush. Unfortunately there is no RadialImageBrush (known to me). I’ve included code to save the image to the disk, and included usings to ensure you import the correct components. This does use WPF but it should work as part of a library or console app.

using System.Windows.Media;
using System.Windows.Media.Imaging;
using System;
using System.Windows.Controls;
using System.Windows;
using System.Windows.Shapes;
namespace WpfApplication30
{
    class ImageEditor
    {
        public static void processImage(string loc)
        {
            ImageSource ic = new BitmapImage(new Uri(loc, UriKind.Relative));
            ImageBrush brush = new ImageBrush(ic);
            Path p = new Path();
            p.Fill = brush;
            CombinedGeometry cb = new CombinedGeometry();
            cb.GeometryCombineMode = GeometryCombineMode.Exclude;
            EllipseGeometry ellipse = new EllipseGeometry(new Point(50, 50), 5, 5);
            RectangleGeometry rect = new RectangleGeometry(new Rect(new Size(100, 100)));
            cb.Geometry1 = rect;
            cb.Geometry2 = ellipse;
            p.Data = cb;

            Canvas inkCanvas1 = new Canvas();
            inkCanvas1.Children.Add(p);
            inkCanvas1.Height = 96;
            inkCanvas1.Width = 96;

            inkCanvas1.Measure(new Size(96, 96));
            inkCanvas1.Arrange(new Rect(new Size(96, 96)));
            RenderTargetBitmap targetBitmap =
    new RenderTargetBitmap((int)inkCanvas1.ActualWidth,
                           (int)inkCanvas1.ActualHeight,
                           96d, 96d,
                           PixelFormats.Default);
            targetBitmap.Render(inkCanvas1);

            using (System.IO.FileStream outStream = new System.IO.FileStream( loc.Replace(".png","Copy.png"), System.IO.FileMode.Create))
            {
                PngBitmapEncoder encoder = new PngBitmapEncoder();
                encoder.Frames.Add(BitmapFrame.Create(targetBitmap));
                encoder.Save(outStream);
            }
        }
    }
}

Here is the result: