How do I create a dynamic mouse cursor .NET without using interop?

Question

I have an application which I\'m interested in eventually porting to mono so I\'m trying to avoid using p/invoke\'s to accomplish this task.

I would like to load a c

Answer 1

The code below creates a stream filled with data in .cur format, which I succesfully tested in Ubuntu with Mono. However .NET without using Win32 API only supports black and white colors in custom cursor:

The Cursor class does not support animated cursors (.ani files) or cursors with colors other than black and white.

Therefore in Unix with Mono one is rewarded with a cursor which

• displays black and white colors only
• has no semi-transparent pixels, only fully opaque / fully transparent ones

¯\_(ツ)_/¯

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace StackoverflowExample
{
    public static class CursorHelper
    {
        public static Cursor CreateCursor(Bitmap bmp, Point hotSpot)
        {
            // https://en.wikipedia.org/wiki/ICO_(file_format)
            var bmpData = bmp.LockBits(new Rectangle(default, bmp.Size), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);

            try
            {
                int numBytes = bmpData.Stride * bmpData.Height;
                var bgraValues = new byte[numBytes];
                Marshal.Copy(bmpData.Scan0, bgraValues, 0, numBytes);

                int max = Math.Max(bmp.Width, bmp.Height);

                if (max > 256)
                    throw new NotSupportedException();

                byte iconSizeByte = _sizes.FirstOrDefault(s => s >= max); // 0 means 256
                int iconSizeI = iconSizeByte == 0 ? 256 : iconSizeByte;
                const int bytesPerPixel = 4;
                const int bytesPerPixelSource = 4;
                byte[] emptyPixel = new byte[bytesPerPixel];

                using (var stream = new MemoryStream())
                using (var writer = new BinaryWriter(stream))
                {
                    writer.Write((ushort)0); // idReserved
                    writer.Write((ushort)2); // idType, 1 = .ico 2 = .cur
                    writer.Write((ushort)1); // idCount

                    writer.Write(iconSizeByte);
                    writer.Write(iconSizeByte);
                    writer.Write((byte)0); // colorCount
                    writer.Write((byte)0); // reserved
                    writer.Write((ushort)hotSpot.X);
                    writer.Write((ushort)hotSpot.Y);

                    var pixelsCount = iconSizeI * iconSizeI;
                    var xorLength = pixelsCount * bytesPerPixel;
                    var andLength = pixelsCount / 8 * 2;

                    writer.Write((uint)(40 + xorLength + andLength)); // sizeInBytes
                    writer.Write((uint)stream.Position + sizeof(uint)); // fileOffset = 22 = 0x16

                    writer.Write(40u); // cursorInfoHeader.biSize
                    writer.Write((int)iconSizeI); // cursorInfoHeader.biWidth
                    writer.Write((int)iconSizeI * 2); // cursorInfoHeader.biHeight
                    writer.Write((ushort)1); // cursorInfoHeader.biPlanes
                    writer.Write((ushort)(8 * bytesPerPixel)); // cursorInfoHeader.biBitCount
                    writer.Write(0u); // cursorInfoHeader.biCompression
                    writer.Write(0u); // cursorInfoHeader.biSizeImage
                    writer.Write(0); // cursorInfoHeader.biXPelsPerMeter;
                    writer.Write(0); // cursorInfoHeader.biYPelsPerMeter;
                    writer.Write(0u); // cursorInfoHeader.biClrUsed = binaryReader2.ReadUInt32();
                    writer.Write(0u); // cursorInfoHeader.biClrImportant = binaryReader2.ReadUInt32();

                    using (var andMask = new MemoryStream(andLength))
                    {
                        byte def = 255;

                        for (int j = 0; j < iconSizeI; j++)
                        {
                            int y = iconSizeI - 1 - j;
                            byte curByte = def;

                            for (int i = 0; i < iconSizeI; i++)
                            {
                                var bitIndex = 7 - i % 8;

                                if (i < bmp.Width && y < bmp.Height)
                                {
                                    var p = y * bmpData.Stride + i * bytesPerPixelSource;
                                    stream.Write(bgraValues, p, bytesPerPixel);

                                    if (bgraValues[p + 3] > 0)
                                        curByte = (byte)(curByte & ~(1 << bitIndex));
                                }
                                else
                                    stream.Write(emptyPixel, 0, emptyPixel.Length);

                                if (bitIndex == 0)
                                {
                                    andMask.WriteByte(curByte);
                                    curByte = def;
                                }
                            }
                        }

                        for (int j = 0; j < iconSizeI; j++)
                            for (int b = 0; b < iconSizeI / 8; b++)
                                andMask.WriteByte(def);

                        andMask.Seek(0, SeekOrigin.Begin);
                        andMask.CopyTo(stream);
                    }

                    stream.Seek(0, SeekOrigin.Begin);

                    // debug
                    // File.WriteAllBytes("/home/kolia/Documents/stream", stream.ToArray());
                    // stream.Seek(0, SeekOrigin.Begin);

                    var cursor = new Cursor(stream);
                    return cursor;
                }
            }
            finally
            {
                bmp.UnlockBits(bmpData);
            }
        }

        private static readonly byte[] _sizes = { 16, 32, 64, 128 };
    }
}