Creating transparent splash screen without any noises

Question

I know How to design a cool semi transparent splash screen.

I have made a png image and set it to the form background image for a C# application.

I have set BackColor and TransparentKey color of the form to Magenta. I've also set the DoubleBuffer to True if that helps.

But when I run the application the form appears with lots of noises around the form.

Is there something I'm missing that I'm not aware of?

Answer 1

I've found a way to solve the problem thanks to Rui Godinho Lopes (rui@Rui lopes.com) Per Pixel Alpha Blend post on codeproject.com

First I added PerPixelAlphaForm to my project.

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



// class that exposes needed win32 gdi functions.
class Win32
{
    public enum Bool
    {
        False= 0,
        True
    };


    [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;
    }


    public const Int32 ULW_COLORKEY = 0x00000001;
    public const Int32 ULW_ALPHA    = 0x00000002;
    public const Int32 ULW_OPAQUE   = 0x00000004;

    public const byte AC_SRC_OVER  = 0x00;
    public const byte AC_SRC_ALPHA = 0x01;


    [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("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 IntPtr CreateCompatibleDC(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);
}



/// <para>Your PerPixel form should inherit this class</para>
/// <author><name>Rui Godinho Lopes</name><email>rui@ruilopes.com</email></author>
public class PerPixelAlphaForm : Form
{
    public PerPixelAlphaForm()
    {
        // This form should not have a border or else Windows will clip it.
        FormBorderStyle = FormBorderStyle.None;
    }


    /// <para>Changes the current bitmap.</para>
    public void SetBitmap(Bitmap bitmap)
    {
        SetBitmap(bitmap, 255);
    }


    /// <para>Changes the current bitmap with a custom opacity level.  Here is where all happens!</para>
    public void SetBitmap(Bitmap bitmap, byte opacity)
    {
        if (bitmap.PixelFormat != PixelFormat.Format32bppArgb)
            throw new ApplicationException("The bitmap must be 32ppp with alpha-channel.");

        // The ideia of this is very simple,
        // 1. Create a compatible DC with screen;
        // 2. Select the bitmap with 32bpp with alpha-channel in the compatible DC;
        // 3. Call the UpdateLayeredWindow.

        IntPtr screenDc = Win32.GetDC(IntPtr.Zero);
        IntPtr memDc = Win32.CreateCompatibleDC(screenDc);
        IntPtr hBitmap = IntPtr.Zero;
        IntPtr oldBitmap = IntPtr.Zero;

        try {
            hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));  // grab a GDI handle from this GDI+ bitmap
            oldBitmap = Win32.SelectObject(memDc, hBitmap);

            Win32.Size size = new Win32.Size(bitmap.Width, bitmap.Height);
            Win32.Point pointSource = new Win32.Point(0, 0);
            Win32.Point topPos = new Win32.Point(Left, Top);
            Win32.BLENDFUNCTION blend = new Win32.BLENDFUNCTION();
            blend.BlendOp             = Win32.AC_SRC_OVER;
            blend.BlendFlags          = 0;
            blend.SourceConstantAlpha = opacity;
            blend.AlphaFormat         = Win32.AC_SRC_ALPHA;

            Win32.UpdateLayeredWindow(Handle, screenDc, ref topPos, ref size, memDc, ref pointSource, 0, ref blend, Win32.ULW_ALPHA);
        }
        finally {
            Win32.ReleaseDC(IntPtr.Zero, screenDc);
            if (hBitmap != IntPtr.Zero) {
                Win32.SelectObject(memDc, oldBitmap);
                //Windows.DeleteObject(hBitmap); // The documentation says that we have to use the Windows.DeleteObject... but since there is no such method I use the normal DeleteObject from Win32 GDI and it's working fine without any resource leak.
                Win32.DeleteObject(hBitmap);
            }
            Win32.DeleteDC(memDc);
        }
    }


    protected override CreateParams CreateParams
    {
        get {
            CreateParams cp = base.CreateParams;
            cp.ExStyle |= 0x00080000; // This form has to have the WS_EX_LAYERED extended style
            return cp;
        }
    }
}

Then I changed my splash screen code like this

namespace MoballeghanPro.Client
{
    public partial class frmSplashScreen : PerPixelAlphaForm
    {
        public frmSplashScreen()
        {
            InitializeComponent();
        }

        private void frmSplashScreen_Load(object sender, EventArgs e)
        {
            SetBitmap(Properties.Resources.IntroMobaleghan); //Png picture in the resources

        }
    }
}

Now the form is shown perfect as I want

Here's the license for the code I used:

// Copyright © 2002-2004 Rui Godinho Lopes <rui@ruilopes.com>
// All rights reserved.
//
// This source file(s) may be redistributed unmodified by any means
// PROVIDING they are not sold for profit without the authors expressed
// written consent, and providing that this notice and the authors name
// and all copyright notices remain intact.
//
// Any use of the software in source or binary forms, with or without
// modification, must include, in the user documentation ("About" box and
// printed documentation) and internal comments to the code, notices to
// the end user as follows:
//
// "Portions Copyright © 2002-2004 Rui Godinho Lopes"
//
// An email letting me know that you are using it would be nice as well.
// That's not much to ask considering the amount of work that went into
// this.
//
// THIS SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
// EXPRESS OR IMPLIED. USE IT AT YOUT OWN RISK. THE AUTHOR ACCEPTS NO
// LIABILITY FOR ANY DATA DAMAGE/LOSS THAT THIS PRODUCT MAY CAUSE.