BitBlt in C# problems

christian de wet

19y7.7kGDI+

Hello all,

I've got some trouble woth using BitBlt in C#. Basically what I would like to achieve is to BitBlt a Bitmap to the Panel Background, replacing all older graphics previously on the Panel Background.

To acheive without BitBlting I can do:

                Graphics g = this.CreateGraphics();
                g.Clear(Color.White);
                g.DrawImageUnscaled(baseBitmap, 0, 0);

baseBitmap is a BitmapImage I created earlier. This works but there's flickering. Plus I would like something faster. The only alternative would be BitBLT.

Now, If I try BitBlt like this:

         Graphics g = Graphics.FromImage(baseBitmapt);
         Graphics g2 = this.CreateGraphics();

            Bitmap targetBMP = new Bitmap(this.Width, this.Height,g);
            Graphics targetG = Graphics.FromImage(targetBMP);
            IntPtr targetHDC = targetG.GetHdc();
            IntPtr gHDC = g.GetHdc();
            IntPtr gHDC2 = g2.GetHdc();

             //Copy baseBitmap to targetBMP
            BitBlt(targetHDC, 0, 0, this.Width, this.Height, gHDC, 0, 0, 13369376);

            //Copy targetBMP to the Panel Background Graphics
            BitBlt(gHDC2, 0, 0, this.Width, this.Height, targetHDC, 0, 0, 13369376);

              targetG.ReleaseHdc(targetHDC);
               g.ReleaseHdc(gHDC);
               g2.ReleaseHdc(gHDC2);

All I get as a result is a blank black screen as the Panel Background Image.

Can anyone help me with this please? I tried looking all over the web, but all samples are in C++ and are slightly complex. Plus I'm just looking for something simple so that I can do this quickly.

Any help will be appreciated.

Thanks

Regards
Nathanael

2 Replies

Know the answer? Post it — somebody with the same question will find it here.

christian de wet19y ago
Wait, the previous example only BitBlts one image. That still works properly, the problem mentioned in my previous post occurs when I BitBlt multiple HBitmaps on each other, like so:

//Below I want to overlay the selectedGeometriesBitmap over baseBitmap and BitBlt this to //the Panel Graphics.

            Graphics sdcGraphics = this.CreateGraphics();
            IntPtr sdc = sdcGraphics.GetHdc();

            IntPtr sourceHBMP = baseBitmap.GetHbitmap();
            IntPtr overlayHBMP = selectedGeometriesBitmap.GetHbitmap();

            IntPtr sourceDC = CreateCompatibleDC(sdc);
            SelectObject(sourceDC, sourceHBMP);

            IntPtr hdc = CreateCompatibleDC(sdc);
            SelectObject(hdc, overlayHBMP);

            BitBlt(sourceDC, 0, 0, this.Width, this.Height, hdc, 0, 0, (int)TernaryRasterOperations.SRCAND);

            BitBlt(sdc, 0, 0, this.Width, this.Height, sourceDC, 0, 0, (int)TernaryRasterOperations.SRCCOPY);

            DeleteDC(sourceDC);
            DeleteDC(hdc);
            ReleaseDC(IntPtr.Zero, sdc);
            DeleteObject(sourceHBMP);
            DeleteObject(overlayHBMP);
            selectedGeometriesBitmap.Dispose();

When I do the above, the colors are distored.

Any ideas?

Thanks
Regards,
Nathanael
christian de wet19y ago
Ok, got it to work, but only half.

What I did was :

            IntPtr sourceHBMP = baseBitmap.GetHbitmap();
                Graphics sdcGraphics = this.CreateGraphics();

                IntPtr sdc = sdcGraphics.GetHdc();

                IntPtr hdc = CreateCompatibleDC(sdc);

                SelectObject(hdc, sourceHBMP);

                BitBlt(sdc, 0, 0, this.Width, this.Height, hdc, 0, 0, 13369376);

                DeleteDC(hdc);
                ReleaseDC(IntPtr.Zero, sdc);
                DeleteObject(sourceHBMP);

So it seems that one needs to create an HBitmap from each bitmap you want to BitBlt. But now, if I do this, the colors are distorted. When BitBlitting the HBitmaps on each other the final image has the result I want but all with the wrong colors. So it seems that the colors get distorted when converting to an HBitmap. Which is not completely acceptable in a GIS commercial app.

Has someone a solution to this?

Thanks for the help

Regards,
Nathanael