c# - 如何将透明光标渲染到保留 alpha channel 的位图？

Question

我使用下面的代码来渲染一个透明图标:

    private void button1_Click(object sender, EventArgs e)
    {
        // using LoadCursorFromFile from user32.dll
        var cursor = NativeMethods.LoadCustomCursor(@"d:\Temp\Cursors\Cursors\aero_busy.ani");

        // cursor -> bitmap
        Bitmap bitmap = new Bitmap(48, 48, PixelFormat.Format32bppArgb);
        Graphics gBitmap = Graphics.FromImage(bitmap);
        cursor.DrawStretched(gBitmap, new Rectangle(0, 0, 32, 32));

        // 1. Draw bitmap on a form canvas
        Graphics gForm = Graphics.FromHwnd(this.Handle);
        gForm.DrawImage(bitmap, 50, 50);

        // 2. Draw cursor directly to a form canvas
        cursor.Draw(gForm, new Rectangle(100, 50, 32, 32));

        cursor.Dispose();
    }

不幸的是，我无法将透明的 Cursor 渲染到 Bitmap!当我直接将 Cursor 绘制到表单 Canvas 时它可以工作，但是当我将 Cursor 绘制到位图时出现问题。非常感谢任何建议。

Answer 1

您现在拥有的解决方案并不完全适用于托管代码。您自己的评论说您正在从 user32.dll P/Invoking LoadCursorFromFile。不管怎样，使用 Win32 API 真的没什么好怕的。

正如我在评论中提到的，您尝试做的事情通常与 GDI+ 绘图函数有关，就像 .NET Framework 提供的大多数函数一样。通过改用 GDI，该任务变得更加容易。 您可以使用以下代码从符合 alpha channel 的光标(或图标，它们基本上可以互换)创建位图:

[StructLayout(LayoutKind.Sequential)]    
private struct ICONINFO
{
    public bool fIcon;
    public int xHotspot;
    public int yHotspot;
    public IntPtr hbmMask;
    public IntPtr hbmColor;
}

[DllImport("user32")]
private static extern bool GetIconInfo(IntPtr hIcon, out ICONINFO pIconInfo);

[DllImport("user32.dll")]
private static extern IntPtr LoadCursorFromFile(string lpFileName);

[DllImport("gdi32.dll", SetLastError = true)]
private static extern bool DeleteObject(IntPtr hObject);

private Bitmap BitmapFromCursor(Cursor cur)
{
    ICONINFO ii;
    GetIconInfo(cur.Handle, out ii);

    Bitmap bmp = Bitmap.FromHbitmap(ii.hbmColor);
    DeleteObject(ii.hbmColor);
    DeleteObject(ii.hbmMask);

    BitmapData bmData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, bmp.PixelFormat);
    Bitmap dstBitmap = new Bitmap(bmData.Width, bmData.Height, bmData.Stride, PixelFormat.Format32bppArgb, bmData.Scan0);
    bmp.UnlockBits(bmData);

    return new Bitmap(dstBitmap);
}

private void Form1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
    //Using LoadCursorFromFile from user32.dll, get a handle to the icon
    IntPtr hCursor = LoadCursorFromFile("C:\\Windows\\Cursors\\Windows Aero\\aero_busy.ani");

    //Create a Cursor object from that handle
    Cursor cursor = new Cursor(hCursor);

    //Convert that cursor into a bitmap
    using (Bitmap cursorBitmap = BitmapFromCursor(cursor))
    {
        //Draw that cursor bitmap directly to the form canvas
        e.Graphics.DrawImage(cursorBitmap, 50, 50);
    }
}

如果此代码无法编译，请确保您已为 System.Drawing、System.Drawing.Imaging 添加了 using 语句> 和 System.Runtime.InteropServices。还要记住将 Form1_Paint 方法连接为表单的 Paint 事件的处理程序。

经测试可以工作: