C# Bitblit from Bitmap to control (Compact Framework)

Question

I used once BitBlt to save a screenshot to an image file (.Net Compact Framework V3.5, Windows Mobile 2003 and later). Worked fine. Now I want to draw a bitmap to a form. I could use this.CreateGraphics().DrawImage(mybitmap, 0, 0), but I was wondering if it would work with BitBlt like before and just swap the params. So I wrote:

[DllImport("coredll.dll")]
public static extern int BitBlt(IntPtr hdcDest, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc, uint dwRop);

(and further down:)

IntPtr hb = mybitmap.GetHbitmap();
BitBlt(this.Handle, 0, 0, mybitmap.Width, mybitmap.Height, hb, 0, 0, 0x00CC0020);

But the form stays plain white. Why is that? Where is the error I commited? Thanks for your opinions. Cheers, David

Answer 1

this.Handle is a Window handle not a device context.

Replace this.Handle with this.CreateGraphics().GetHdc()

Of course you'll need to destroy the graphics object etc...

IntPtr hb = mybitmap.GetHbitmap(); 
using (Graphics gfx = this.CreateGraphics())
{
  BitBlt(gfx.GetHdc(), 0, 0, mybitmap.Width, mybitmap.Height, hb, 0, 0, 0x00CC0020);
}

In addition hb is a Bitmap Handle not a device context so the above snippet still won't work. You'll need to create a device context from the bitmap:

    using (Bitmap myBitmap = new Bitmap("c:\test.bmp"))
    {
        using (Graphics gfxBitmap = Graphics.FromImage(myBitmap))
        {
            using (Graphics gfxForm = this.CreateGraphics())
            {
                IntPtr hdcForm = gfxForm.GetHdc();
                IntPtr hdcBitmap = gfxBitmap.GetHdc();
                BitBlt(hdcForm, 0, 0, myBitmap.Width, myBitmap.Height, hdcBitmap, 0, 0, 0x00CC0020);
                gfxForm.ReleaseHdc(hdcForm);
                gfxBitmap.ReleaseHdc(hdcBitmap);
            }
        }
    }