BitBlt code not working

Question

I\'m trying to use this code to draw a Bitmap directly onto a PictureBox:

Bitmap bmp = (Bitmap)Bitmap.FromFile(@\"C:\\Users\\Ken\\D         


        

Answer 1

This is because a device context contains a 1x1 black bitmap until SelectObject is used. For whatever reason, Graphics.FromImage is giving you a device context that is compatible with the bitmap, but it does not automatically select the bitmap into the device context.

The following code will use SelectObject.

You should, of course, use the managed Graphics.DrawImage instead of BitBlt if possible, but I assume that you have a good reason for using BitBlt.

private void Draw()
{
    using (Bitmap bmp = (Bitmap)Bitmap.FromFile(@"C:\Jason\forest.jpg"))
    using (Graphics grDest = Graphics.FromHwnd(pictureBox1.Handle))
    using (Graphics grSrc = Graphics.FromImage(bmp))
    {
        IntPtr hdcDest = IntPtr.Zero;
        IntPtr hdcSrc = IntPtr.Zero;
        IntPtr hBitmap = IntPtr.Zero;
        IntPtr hOldObject = IntPtr.Zero;

        try
        {
            hdcDest = grDest.GetHdc();
            hdcSrc = grSrc.GetHdc();
            hBitmap = bmp.GetHbitmap();

            hOldObject = SelectObject(hdcSrc, hBitmap);
            if (hOldObject == IntPtr.Zero)
                throw new Win32Exception();

            if (!BitBlt(hdcDest, 0, 0, pictureBox1.Width, pictureBox1.Height,
                hdcSrc, 0, 0, 0x00CC0020U))
                throw new Win32Exception();
        }
        finally
        {
            if (hOldObject != IntPtr.Zero) SelectObject(hdcSrc, hOldObject);
            if (hBitmap != IntPtr.Zero) DeleteObject(hBitmap);
            if (hdcDest != IntPtr.Zero) grDest.ReleaseHdc(hdcDest);
            if (hdcSrc != IntPtr.Zero) grSrc.ReleaseHdc(hdcSrc);
        }
    }
}

[DllImport("gdi32.dll", EntryPoint = "SelectObject")]
public static extern System.IntPtr SelectObject(
    [In()] System.IntPtr hdc,
    [In()] System.IntPtr h);

[DllImport("gdi32.dll", EntryPoint = "DeleteObject")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool DeleteObject(
    [In()] System.IntPtr ho);

[DllImport("gdi32.dll", EntryPoint = "BitBlt")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool BitBlt(
    [In()] System.IntPtr hdc, int x, int y, int cx, int cy,
    [In()] System.IntPtr hdcSrc, int x1, int y1, uint rop);