Graphics

private Bitmap _transImage = null;

public Form1()
{
    InitializeComponent();
}

~Form1()
{
    _transImage.Dispose();
}

protected override void OnLoad(EventArgs e)
{
    Bitmap b = new Bitmap(@"c:\myImage.png");

    _transImage = AdjustImageTransparency(b);

    b.Dispose();

    base.OnLoad(e);
}

protected override void OnPaint(PaintEventArgs e)
{
    e.Graphics.DrawImage(_transImage, new Rectangle(40, 40, _transImage.Width, _transImage.Height));

    base.OnPaint(e);
}

private Bitmap AdjustImageTransparency(Bitmap sourceImage)
{
    // image must be 32bpp to allow transparency adjustment, so paint source to transImage gc
    Bitmap transImage = new Bitmap(sourceImage.Width, sourceImage.Height, PixelFormat.Format32bppArgb);
    Rectangle rc = new Rectangle(Point.Empty, sourceImage.Size);

    using (Graphics g = Graphics.FromImage(transImage))
        g.DrawImage(sourceImage, rc);

    // lock transImage for direct memory manipulation
    BitmapData bd = transImage.LockBits(rc, ImageLockMode.ReadWrite, transImage.PixelFormat);

    AdjustTransparency(bd, 0.5f);

    // must always unlock the memory when finished
    transImage.UnlockBits(bd);

    return transImage;
}

private unsafe void AdjustTransparency(BitmapData dataObj, float ratio)
{
    // calc the number of bytes that represent a single row
    int byteWidth = dataObj.Width * 4;

    for (int y = 0; y < dataObj.Height; y++)
    {
        // calc memory location for row(y)
        byte* row = (byte*)dataObj.Scan0 + dataObj.Stride * y;

        for (int x = 0; x < byteWidth; x++)
        {
            // every 4th byte in a 32bpp image is the alpha value for each pixel
            if ((x % 4) == 3)
            {
                // adjust value of transparency byte according to ratio (0-1 value)
                float val = (float)row[x];
                val *= ratio;
                val = Math.Min(Math.Max(val, 0), 255);

                row[x] = (byte)val;
            }
        }
    }
}

Vlasta_ wrote:

but unfortunately, the same "heuristics" applies to CreateDIBSection as well.

Vlasta_ wrote:

I ended up using CreateIconFromResourceEx & DrawIconEx combination.

Mark Salsbery
Microsoft MVP - Visual C++