R – Windows Forms .NET 2.0: How to draw a PNG icon

graphicsnetwindows-vistawinforms

Note: Question Using 256 x 256 Vista icon in application deals with using a "Vista" icon as the application's icon. This question deals with manually painting a Vista icon.

Note: Question WinForms .NET 2.0: How to paint the proper sized icon? deals with painting a Vista icon loaded from a file. This question deals with painting a Vista icon that is loaded from a .resource.

I've included an icon in my Visual Studio project that has various formats:

  • 16×16
  • 32×32
  • 48×48
  • 256×256 (PNG compressed)

Now want to draw the 256×256 version. None of the following things I've tried work.

The following draws the 32×32 format stretched to 256×256:

Icon ico = Properties.Resources.TestIconThatHasA256PNGFormat;
e.Graphics.DrawIcon(ico, new Rectangle(0, 0, 256, 256));

The following draws the 32×32 format unstretched:

Icon ico = Properties.Resources.TestIconThatHasA256PNGFormat;
e.Graphics.DrawIconUnstretched(ico, new Rectangle(0, 0, 256, 256));

The following draws the 32×32 format stretched to 256×256:

Icon ico = Properties.Resources.TestIconThatHasA256PNGFormat;
e.Graphics.DrawImage(ico.ToBitmap(), new Rectangle(0, 0, 256, 256));

The following draws the 48×48 format stretched to 256×256:

Icon ico = Properties.Resources.TestIconThatHasA256PNGFormat;
e.Graphics.DrawIcon(
      new Icon(ico, new Size(256, 256)),
      new Rectangle(0, 0, 256, 256));

How do I draw the 256×256 format icon?

Notes:

  1. The icon is not coming from a file, so PInvoking LoadImage() will not help.

  2. The icon is not the icon associated with a file, so PInvoking SHGetFileInfo() will not help. Nor will using Icon.ExtractAssociatedIcon.

  3. I'm also not trying to author icons with a 256×256 format at runtime, so libraries designed to do that will not help.

    2: Question WinForms .NET 2.0: How to paint the proper sized icon?

Best Answer

The ResourceManager loads the icon based on the bits stored in the resources. However, the way it handles loading won't let you access the 256x256 icon (this information does not make its way into the System.Drawing.Icon that you are getting back).

I am sorry to disappoint you, but the only way which works that I am aware of is to load the icon through a P/Invoke of LoadImage and working with a file (yes, I know, that's not what you were looking for). So the new question should be: how do I extract the bits of a given resource so that I can store them to a file? I fear that this isn't possible either, having done some stepping through System.Resources.ResourceReader, as the resource data seems to be a collection of serialized .NET objects.

Anyway, for those who can afford to load the icon from a .ICO file (and for myself, as a future reference on how to load 256x256 icons), call IconConverter.LoadIcon:

using System.Runtime.InteropServices;

static class IconConverter
{
    public static System.Drawing.Icon LoadIcon(string path, int width, int height)
    {
        System.IntPtr hIcon;
        hIcon = LoadImage (System.IntPtr.Zero, path, IMAGE_ICON, width, height,
                           LR_LOADFROMFILE);
        if (hIcon == System.IntPtr.Zero)
        {
            return null;
        }
        return System.Drawing.Icon.FromHandle (hIcon);
    }

    const int IMAGE_ICON = 1;
    const int LR_LOADFROMFILE = 0x0010;

    [DllImport ("user32.dll", SetLastError=true, CharSet=CharSet.Auto)]
    static extern System.IntPtr LoadImage(System.IntPtr hInstance,
                                          string lpszName, uint uType,
                                          int cxDesired, int cyDesired,
                                          uint fuLoad);
}

Once you have the System.Drawing.Icon in the expected size, just paint it using graphics.DrawIconUnstretched.

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