I'm trying to use this code to draw a Bitmap
directly onto a PictureBox
:
Bitmap bmp = (Bitmap)Bitmap.FromFile(@"C:\Users\Ken\Desktop\Load2.bmp");
Graphics grDest = Graphics.FromHwnd(pictureBox1.Handle);
Graphics grSrc = Graphics.FromImage(bmp);
IntPtr hdcDest = grDest.GetHdc();
IntPtr hdcSrc = grSrc.GetHdc();
BitBlt(hdcDest, 0, 0, pictureBox1.Width, pictureBox1.Height,
hdcSrc, 0, 0, (uint)TernaryRasterOperations.SRCCOPY); // 0x00CC0020
grDest.ReleaseHdc(hdcDest);
grSrc.ReleaseHdc(hdcSrc);
but instead of rendering the Bitmap
's contents it just draws a solid block of nearly-black. I'm pretty sure the problem is with the source hDC, because if I change SRCCOPY to WHITENESS in the above code, it draws a solid white block, as expected.
Note: this next snippet works fine, so there's nothing wrong with the bitmap itself:
Bitmap bmp = (Bitmap)Bitmap.FromFile(@"C:\Users\Ken\Desktop\Load2.bmp");
pictureBox1.Image = bmp;
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);