Icons and cursors

Dapplo.Windows.Icons extracts icons from files and the shell, writes ICO and CUR files, and captures the mouse cursor, for example to draw it into a screenshot. The icon of a window is in the main package, see Window management.

dotnet add package Dapplo.Windows.Icons

Namespaces used on this page: Dapplo.Windows.Icons, Dapplo.Windows.Icons.Enums, Dapplo.Windows.Common.Structs, Dapplo.Windows.User32.

The generic methods (<TIcon>) return System.Drawing.Icon or Bitmap; other types throw a NotSupportedException. For WPF convert the result with ToBitmapSource() from Dapplo.Windows.Wpf. Returned icons own their handle, dispose them.

Extracting icons

// The first icon of an executable or DLL, TIcon is Icon or Bitmap
using var notepadIcon = IconHelper.ExtractAssociatedIcon<Icon>(@"C:\Windows\notepad.exe");

// How many icons a file has, and one of them in the small size
int count = IconHelper.CountAssociatedIcons(@"C:\Windows\System32\shell32.dll");
using var smallIcon = IconHelper.ExtractAssociatedIcon<Bitmap>(@"C:\Windows\System32\shell32.dll", index: 3, useLargeIcon: false);

// The icon Explorer shows for a file type, the file doesn't need to exist
using var pdfIcon = IconHelper.GetFileExtensionIcon<Bitmap>("document.pdf", IconSize.Large, linkOverlay: false);

// The folder icon
using var folderIcon = IconHelper.GetFolderIcon<Icon>(IconSize.Small, FolderIconType.Closed);

IconHelper.GetAppLogo<Bitmap>(exePath) reads the logo of a store (UWP / MSIX) app from its AppxManifest, and IconHelper.LoadIconWithScaleDown / LoadIconWithSystemMetrics load icon resources at a size.

The sizes of the system:

// The icon sizes of the system, they depend on the DPI of the process
Size small = new Size(IconHelper.GetSmallIconWidth(), IconHelper.GetSmallIconHeight());
Size standard = new Size(IconHelper.GetStandardIconWidth(), IconHelper.GetStandardIconHeight());

Writing ICO files

IconFileWriter.WriteIconFile writes one ICO with an image per size. Every image is stored as PNG, which Windows Vista and later read; images larger than 256 x 256 are scaled down to fit.

// One image per size. Every image is stored as PNG (Windows Vista and later), larger than 256x256 is scaled down.
var images = new List<Image>();
foreach (var size in new[] { 16, 32, 48, 256 })
{
    var bitmap = new Bitmap(size, size);
    using (var graphics = Graphics.FromImage(bitmap))
    {
        graphics.Clear(Color.Transparent);
        graphics.FillEllipse(Brushes.SteelBlue, 0, 0, size - 1, size - 1);
    }
    images.Add(bitmap);
}

IconFileWriter.WriteIconFile("app.ico", images);

// Or into a stream
using (var stream = new MemoryStream())
{
    IconFileWriter.WriteIconFile(stream, images);
}

images.ForEach(image => image.Dispose());

Writing CUR files

A cursor also needs the hot spot, the pixel which "clicks":

using var cursorImage = new Bitmap(32, 32);
using (var graphics = Graphics.FromImage(cursorImage))
{
    graphics.DrawLine(Pens.Black, 16, 0, 16, 31);
    graphics.DrawLine(Pens.Black, 0, 16, 31, 16);
}

// The hot spot is the pixel which "clicks", here the center of the cross
IconFileWriter.WriteCursorFile("cross.cur", new[] { ((Image)cursorImage, new Point(16, 16)) });

Capturing the mouse cursor

CursorHelper.TryGetCurrentCursor captures the current cursor with its color and mask layers, its Size and its HotSpot, also for large pointer sizes and high DPI. DrawCursorOnBitmap / DrawCursorOnGraphics draw it; the position is the top-left of the cursor image, so subtract the hot spot to draw it at the mouse position.

// Capture the current mouse cursor (also high DPI and animated system cursors, the current frame)
if (CursorHelper.TryGetCurrentCursor(out var cursor))
{
    using (cursor)
    {
        // Draw it into a screenshot: the position is the top-left of the cursor image, so subtract the hot spot
        var mouse = User32Api.GetCursorLocation();
        var position = new NativePoint(mouse.X - cursor.HotSpot.X - screenshotLocation.X, mouse.Y - cursor.HotSpot.Y - screenshotLocation.Y);
        CursorHelper.DrawCursorOnBitmap(screenshot, cursor, position);
    }
}

The file format

For your own tools the structures of the format are available in Dapplo.Windows.Icons.Structs:

IconDir / IconDirEntry: the ICONDIR header and the ICONDIRENTRY of each image in an .ico or .cur file (CreateIcon / CreateCursor, CreateForIcon / CreateForCursor).
GrpIconDir / GrpIconDirEntry: the same for icon resources in executables, where an entry refers to a resource id instead of a file offset. IconFileWriter.WriteGrpIconDir / WriteGrpIconDirEntry write them.

An ICO file is a 6-byte ICONDIR (reserved, type 1 = icon or 2 = cursor, count), a 16-byte ICONDIRENTRY per image (width and height where 0 means 256, color count, planes or hot spot X, bit count or hot spot Y, size, offset) and the image data (PNG or BMP without the file header).