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Smooth Sliding Graphics Object

Posted on 2003-02-22
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Last Modified: 2012-06-21
Using VC7, C++, no direct-x or open/gl. How can I smoothly slide an object(bitmap) across a bitmap background. I need to slide it slowly and smoothly in various directions. i.e. sliding a chess piece, etc.
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Question by:_kp
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4 Comments
 

Author Comment

by:_kp
ID: 8000577
Forgot to mention, windows MFC platform.
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Accepted Solution

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imadjinn earned 200 total points
ID: 8000799
Here is a VERY useful class that I use for this task.  In your OnPaint (or wherever) create a CMemDC and pass the DC you created in to it.  Since it is dervied from CDC directly you can use it interchangeably with CPaintDC as well.

#ifndef _MEMDC_H_
#define _MEMDC_H_

//////////////////////////////////////////////////
// CMemDC - memory DC
//
// Author: Keith Rule
// Email:  keithr@europa.com
// Copyright 1996-2002, Keith Rule
//
// You may freely use or modify this code provided this
// Copyright is included in all derived versions.
//
// History - 10/3/97 Fixed scrolling bug.
//                   Added print support. - KR
//
//           11/3/99 Fixed most common complaint. Added
//                   background color fill. - KR
//
//           11/3/99 Added support for mapping modes other than
//                   MM_TEXT as suggested by Lee Sang Hun. - KR
//
//           02/11/02 Added support for CScrollView as supplied
//                    by Gary Kirkham. - KR
//
// This class implements a memory Device Context which allows
// flicker free drawing.

class CMemDC : public CDC {
private:    
     CBitmap          m_bitmap;          // Offscreen bitmap
     CBitmap*     m_oldBitmap;     // bitmap originally found in CMemDC
     CDC*          m_pDC;               // Saves CDC passed in constructor
     CRect          m_rect;               // Rectangle of drawing area.
     BOOL          m_bMemDC;          // TRUE if CDC really is a Memory DC.
public:
     
     CMemDC(CDC* pDC, const CRect* pRect = NULL) : CDC()
     {
          ASSERT(pDC != NULL);

          // Some initialization
          m_pDC = pDC;
          m_oldBitmap = NULL;
          m_bMemDC = !pDC->IsPrinting();

          // Get the rectangle to draw
          if (pRect == NULL) {
               pDC->GetClipBox(&m_rect);
          } else {
               m_rect = *pRect;
          }

          if (m_bMemDC) {
               // Create a Memory DC
               CreateCompatibleDC(pDC);
               pDC->LPtoDP(&m_rect);

               m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
               m_oldBitmap = SelectObject(&m_bitmap);

               SetMapMode(pDC->GetMapMode());

               SetWindowExt(pDC->GetWindowExt());
               SetViewportExt(pDC->GetViewportExt());

               pDC->DPtoLP(&m_rect);
               SetWindowOrg(m_rect.left, m_rect.top);
          } else {
               // Make a copy of the relevent parts of the current DC for printing
               m_bPrinting = pDC->m_bPrinting;
               m_hDC       = pDC->m_hDC;
               m_hAttribDC = pDC->m_hAttribDC;
          }

          // Fill background
          FillSolidRect(m_rect, pDC->GetBkColor());
     }
     
     ~CMemDC()    
     {          
          if (m_bMemDC) {
               // Copy the offscreen bitmap onto the screen.
               m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
                    this, m_rect.left, m_rect.top, SRCCOPY);              
               
               //Swap back the original bitmap.
               SelectObject(m_oldBitmap);          
          } else {
               // All we need to do is replace the DC with an illegal value,
               // this keeps us from accidently deleting the handles associated with
               // the CDC that was passed to the constructor.              
               m_hDC = m_hAttribDC = NULL;
          }    
     }
     
     // Allow usage as a pointer    
     CMemDC* operator->()
     {
          return this;
     }    

     // Allow usage as a pointer    
     operator CMemDC*()
     {
          return this;
     }
};

#endif
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Author Comment

by:_kp
ID: 8001254
Thanks for the info. Actually I'm already using that code. Guess you're right, it's pretty popular. ;) My question is more related to the animation...I have a small group of separate bitmaps that I want to blit seperately to an off screen empty buffer (a group of chips) using DrawTransparentBitmap(), then take that new image using DrawTransparentBitmap() to move it onto the screen and then draw/step/erase/etc. to allow moning them smoothly around the screen. Basically create a bitmap of all the little bitmaps in the collection, and move that one bitmap.
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Author Comment

by:_kp
ID: 8001814
Update to previous question. I have it sort of working.
The problem now is I have a bitmap that I created with CreateCompatibleBitmap() and BltBlt'd into, in a CDC that I need to get a CBitmap reference to so I can prepare a mask for use with DrawTransparentBitmap(). How do I get/create the CBitmap I need from the CDC?
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