How to design a cool semi transparent splash screen? – Photoshop

This question is old, but I decided to chime in because it’s the first result for “transparent splash screen C#”, and Tolga’s solution can produce strange borders with the color of the TransparencyKey around some edges of the image. This is more evident if it has lines anti-aliased with semitransparent pixels.

I copied this code from here. Unfortunately, neither I nor the poster know the original author.

I’ve also made some modifications to support changing the form’s opacity.

Splash.cs:

class Splash : Form {
    private float _opacity = 1.0f;
    public Bitmap BackgroundBitmap;

    public new float Opacity {
        get {
            return _opacity;
        }
        set {
            _opacity = value;
            SelectBitmap(BackgroundBitmap);
        }
    }

    public Splash(Bitmap bitmap) {
        // Window settings   
        this.TopMost = true;
        this.ShowInTaskbar = false;
        this.Size = bitmap.Size;
        this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
        // Must be called before setting bitmap   
        this.BackgroundBitmap = bitmap;
        this.SelectBitmap(BackgroundBitmap);
        this.BackColor = Color.Red;
    }

    // Sets the current bitmap
    public void SelectBitmap(Bitmap bitmap) {
        // Does this bitmap contain an alpha channel?   
        if (bitmap.PixelFormat != PixelFormat.Format32bppArgb) {
            throw new ApplicationException("The bitmap must be 32bpp with alpha-channel.");
        }
        // Get device contexts   
        IntPtr screenDc = APIHelp.GetDC(IntPtr.Zero);
        IntPtr memDc = APIHelp.CreateCompatibleDC(screenDc);
        IntPtr hBitmap = IntPtr.Zero;
        IntPtr hOldBitmap = IntPtr.Zero;
        try {
            // Get handle to the new bitmap and select it into the current device context      
            hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));
            hOldBitmap = APIHelp.SelectObject(memDc, hBitmap);
            // Set parameters for layered window update      
            APIHelp.Size newSize = new APIHelp.Size(bitmap.Width, bitmap.Height);
            // Size window to match bitmap      
            APIHelp.Point sourceLocation = new APIHelp.Point(0, 0);
            APIHelp.Point newLocation = new APIHelp.Point(this.Left, this.Top);
            // Same as this window      
            APIHelp.BLENDFUNCTION blend = new APIHelp.BLENDFUNCTION();
            blend.BlendOp = APIHelp.AC_SRC_OVER;
            // Only works with a 32bpp bitmap      
            blend.BlendFlags = 0; // Always 0   
            blend.SourceConstantAlpha = (byte)(Opacity * 255); // Set to 255 for per-pixel alpha values
            blend.AlphaFormat = APIHelp.AC_SRC_ALPHA;
            // Only works when the bitmap contains an alpha channel      
            // Update the window      
            APIHelp.UpdateLayeredWindow(Handle, screenDc, ref newLocation, ref newSize, memDc, ref sourceLocation, 0, ref blend, APIHelp.ULW_ALPHA);
        } finally {
            // Release device context      
            APIHelp.ReleaseDC(IntPtr.Zero, screenDc);
            if (hBitmap != IntPtr.Zero) {
                APIHelp.SelectObject(memDc, hOldBitmap);
                APIHelp.DeleteObject(hBitmap);
                // Remove bitmap resources      
            }
            APIHelp.DeleteDC(memDc);
        }
    }

    protected override CreateParams CreateParams {
        get {
            // Add the layered extended style (WS_EX_LAYERED) to this window      
            CreateParams createParams = base.CreateParams;
            createParams.ExStyle |= APIHelp.WS_EX_LAYERED;
            return createParams;
        }
    }

    // Let Windows drag this window for us (thinks its hitting the title bar of the window)
    protected override void WndProc(ref Message message) {
        if (message.Msg == APIHelp.WM_NCHITTEST) {
            // Tell Windows that the user is on the title bar (caption)      
            message.Result = (IntPtr)APIHelp.HTCAPTION;
        } else {
            base.WndProc(ref message);
        }
    }
}

APIHelp.cs:

// Class to assist with Win32 API calls
class APIHelp { 
    public const Int32 WS_EX_LAYERED = 0x80000;
    public const Int32 HTCAPTION = 0x02;
    public const Int32 WM_NCHITTEST = 0x84;
    public const Int32 ULW_ALPHA = 0x02;
    public const byte AC_SRC_OVER = 0x00;
    public const byte AC_SRC_ALPHA = 0x01;

    public enum Bool {
        False = 0, True = 1
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct Point {
        public Int32 x;
        public Int32 y;
        public Point(Int32 x, Int32 y) {
            this.x = x;
            this.y = y;
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct Size {
        public Int32 cx;
        public Int32 cy;
        public Size(Int32 cx, Int32 cy) {
            this.cx = cx;
            this.cy = cy;
        }
    }

    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    struct ARGB {
        public byte Blue;
        public byte Green;
        public byte Red;
        public byte Alpha;
    }

    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    public struct BLENDFUNCTION {
        public byte BlendOp;
        public byte BlendFlags;
        public byte SourceConstantAlpha;
        public byte AlphaFormat;
    }

    [DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
    public static extern Bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref Point pptDst, ref Size psize, IntPtr hdcSrc, ref Point pprSrc, Int32 crKey, ref BLENDFUNCTION pblend, Int32 dwFlags);

    [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
    public static extern IntPtr CreateCompatibleDC(IntPtr hDC);

    [DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
    public static extern IntPtr GetDC(IntPtr hWnd);

    [DllImport("user32.dll", ExactSpelling = true)]
    public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

    [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
    public static extern Bool DeleteDC(IntPtr hdc);

    [DllImport("gdi32.dll", ExactSpelling = true)]
    public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);

    [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
    public static extern Bool DeleteObject(IntPtr hObject);
}