Using GDI+ in a Single Document MFC Project to Rotate, Zoom, and Constraint an Image

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• Download demo project - 23.79 KB

Introduction

The program loads images (BMP, GIF, JPEG/JPG/EXIF, PNG, TIF, ICON, WMF, EMF), applies some constraints related to window size (best fit, constraint width, constraint height, image original), rotates the image, makes zoom in & out effect and finally navigates through multi-page TIF images. It is useful if you need a image viewer class and image functionality in your C++ application. The problem is that I use GDI+. Developing with GDI+, there is a point most of us must go through.

First, go beyond pointers to GDI+ Image class that block access to every image file I load and view; now only the current loaded is blocked. No more headache with blocked temp image files, we got the key. How to make a big JPEG/JPG/EXIF move fast? I made it, but unfortunately it won't work for a rotation with 180 degrees. Just stretch the image in a hidden window: rotate 90 degrees Graphics::RotateTransform(...) , and display image, don't ask why! It will work to your surprise. I found many programmers that rotated an image with Image class method RotateFlip (and I did it too), instead of Graphics class method RotateTransform. This implies that an image will have negative values along X, Y axis and more ... but will have intact integrity of its internal structure. What I didn't solve is transparent background images management, and what to do to cheat image at a 180 angle rotation.

Background

C/C++ is great, but to know it from the very beginning.

Using the Code

The class that do everything that I discussed earlier is mvImage. So you will need this #include "mvImage.h" in your application. The mvImage class constructor needs a window handle HWND. The rest does the class through this handle. You can use this class in a single / multi document interface or dialog based MFC project. I will try a poor demonstration copying parts of the code here to show you: easier than this doesn't exist !

1. Your CView derived class constructor will be like this:

   CDraw1View::CDraw1View() { m_Image = 0x000000 ; }

• 2.1 Initialization of mvImage pointer comes in OnDraw once per application, the rest is redrawing the window surface.

  void CDraw1View::OnDraw(CDC* pDC)
  { 
      CDraw1Doc* pDoc = GetDocument(); 
      ASSERT_VALID(pDoc); 
  
      // TODO: add draw code for native data here 
      //init image pointer 
      if((m_Image == 0x000000) && (this->m_hWnd != 0x000000)) 
      { 
          m_Image = new mvImage(this->m_hWnd); 
      }//if 
      else
      {
          //redraw image window 
          if(m_Image->mvIsValidImage()) m_Image->mvOnPaint(); 
      } 
  }

• 2.2 If your application is dialog based, use OnInitDialog to put this code in:

  .....
  
  if((m_Image == 0x000000) && (this->m_hWnd != 0x000000))
  { 
      m_Image = new mvImage(this->m_hWnd);
  }//if
  
  .....

  and OnPaint method with this code:

  if(m_Image->mvIsValidImage()) m_Image->mvOnPaint() ;

3. To load and display an image with 'best fit' propriety, use this:

   .....
   
   CFileDialog Fdlg(TRUE) ;
   if(Fdlg.DoModal() == IDOK)
   {
       CString path = Fdlg.GetPathName() ; 
       m_Image->mvLoadImage(path) ;
   }//if
   else return ;
   
   //display image 'best fit' in wind.
   if(m_Image->mvIsValidImage()) m_Image->mvConstraintAll();
   
   .....

4. Constraint all 'best fit' image in window, proceed like here:

   if(m_Image->mvIsValidImage())
   {
       m_Image->mvConstraintAll();
   }

5. Constraint height ? like here:

   if(m_Image->mvIsValidImage())
       m_Image->mvConstraintHeight() ;

6. Rotate left:

   if(m_Image->mvIsValidImage())
       m_Image->mvRotateLeft() ;

7. Zoomin:

   if(m_Image->mvIsValidImage())
       m_Image->mvZoomIn() ;

8. Entire vertical scroll function:

   void CDraw1View::OnVScroll(UINT nSBCode, UINT nPos, CScrollBar* pScrollBar)
   {
       // TODO: Add your message handler code here and/or call default
       if(m_Image->mvIsValidImage())
           m_Image->mvOnVScroll(nSBCode, nPos, pScrollBar) ;
   
       CView::OnVScroll(nSBCode, nPos, pScrollBar);
   }

9. Route OnSize message like this:

   void CDraw1View::OnSize(UINT nType, int cx, int cy)
   {
       CView::OnSize(nType, cx, cy);
   
       if((m_Image != 0x000000) && (this->m_hWnd != 0x000000))
       {
           if(m_Image->mvIsValidImage()) 
               m_Image->mvOnSize(nType, cx, cy) ; 
       }
   }

10. Multi-page TIFF navigation:

    if(m_Image->mvIsValidImage())
        m_Image->mvFrameFirst();

Searching through the source code in draw1View.cpp, you will find all the code you may be interested in.

History

• 27^th August, 2006: Initial post