Graphics

// Load two bitmaps from resources
pja::CBitmap bmp1(IDB_BITMAP1);
pja::CBitmap bmp2(IDB_BITMAP2);

// create a monochrome bitmap the same size as the resource bitmaps
pja::CBitmap bmpbw = CreateBitmap(bmp1.Width(), bmp1.Height(), 1, 1, NULL);

ShowGraphic(bmp1);
ShowGraphic(bmp2);

// Create compatible device contexts, compatible with the display
pja::CCompatibleDC dc1;
pja::CCompatibleDC dc2;
pja::CCompatibleDC dcbw;

// Select the bitmaps into the device contexts
SelectObject(dc1, bmp1);
SelectObject(dc2, bmp2);
SelectObject(dcbw, bmpbw);

// Combine the two resource bitmaps using the DSxn ROP.
// Source bitmap is inverted then XORed with the destination bitmap
// This results in the destination bitmap having white pixels where the
// two bitmaps matched, and other colours where they are different
BitBlt(dc1, 0, 0, bmp1.Width(), bmp1.Height(), dc2, 0, 0, 0x00990066);
ShowGraphic(dc1);

// Copy the new bitmap onto the monochrome bitmap
// White stays white, rest turns black
SetBkColor(dc1, RGB(255, 255, 255));
BitBlt(dcbw, 0, 0, bmpbw.Width(), bmpbw.Height(), dc1, 0, 0, SRCCOPY);
ShowGraphic(bmpbw);

SelectObject (dc1, GetStockObject(WHITE_BRUSH));
PatBlt (dc1, 0, 0, bmp1.Width(), bmp1.Height(), 0x00A000C9);

Richard A. Abbott wrote:

Don't know how deep your pockets are

Richard A. Abbott wrote:

but you might find this interesting reading

class SomeForm : Form
{
  private Bitmap _theImage;
  private bool _working = false;

  void worker_DoWork(object sender, DoWorkEventArgs e)
  {
    // make sure the image is initialized (may as well do it on the background thread).
    if (_theImage == null)
    {
      int width = (int)Math.Round(Width * fDPIX);
      int height = LogHeightPixels;
      _theImage = new Bitmap(width, height/*, System.Drawing.Imaging.PixelFormat.Gdi/*.Format32bppArgb*/);
    }
    // note, you may need to clear the bitmap in this method call.
    // it all depends on what the draw log method is doing.
    DrawLogToBitmap(_theImage);
  }

  void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
  {
    _working = false;
    Refresh();
  }

  public override void Draw(Graphics gfx, Rectangle rect)
  {
    gfx.ScaleTransform(zoom, zoom);

    // Update the bitmap (only as needed)
    if (bDirty)
    {
       // I'm assuming this method starts the worker thread - if so:
       _working = true;
       UpdateBitmap(gfx);
    }

    if (_working || worker.IsBusy)
    {
       gfx.DrawString("Updating Bitmap, please wait!", this.Font, Brushes.Black, new PointF(0, 0));
       return;
    }

    RectangleF rcSource = new RectangleF(-horizontalOffset, -verticalOffset, ClientRectangle.Width/zoom, ClientRectangle.Height/zoom);
    RectangleF rcDest = new RectangleF(ClientRectangle.Location.X, ClientRectangle.Location.Y, ClientRectangle.Size.Width/zoom, ClientRectangle.Size.Height/zoom);

    try
    {
       gfx.DrawImage(_theImage, rcDest, rcSource, GraphicsUnit.Pixel);
    }
    catch (Exception exc)
    {
       gfx.DrawString(exc.Message, Font, Brushes.Black, new PointF(0,0));
    }
    etc....
  }
}