• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 323
  • Last Modified:

How to draw a picture in the background without flickering on scrolling?

I am trying to draw a picture in the background of my control, the picture is determined in a property called Picture from the type CPictureHolder. I need to draw this picture in a way to get rid of flickering while scrolling or resizing. I have tried several methods but seems that I am missing something! Is it possible to have this functionality??
1 Solution
You can draw it in OnPaint.
To get rid of flicking, you can use CMemDC to instead of CDC object in OnPaint().
See the example here:
And the following is CMemDC:
//Include it in your CPP file
#ifndef _MEMDC_H_
#define _MEMDC_H_

class CMemDC : public CDC
     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.

     CMemDC(CDC* pDC, CRect rect = CRect(0,0,0,0)) : CDC(), m_oldBitmap(NULL), m_pDC(pDC)
          ASSERT(m_pDC != NULL); // If you asserted here, you passed in a NULL CDC.
          m_bMemDC = !pDC->IsPrinting();
          if (m_bMemDC){
               // Create a Memory DC
               if ( rect == CRect(0,0,0,0) )
                    m_rect = rect;

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

You should override Render() in your CPictureHolder-derived class.  Then draw it only when necessary.  Use ValidateRect() and/or ValidateRgn()to mask parts of the picture that are not being changed by the user-activity.

As IProgram said, using a memory DC might help.

-- Dan
DaedAuthor Commented:
I tried using the CMemDC in OnPaint(), but my problem is that i need to write over the background picture, and this happens on DrawItem of another class, so when using the CMemDC there also, the new writtings are drawn over the picture (on a white rect) and hide it. How can i write over the background picture without any mixing in the colors and no flickering as well!
Roshan DavisCommented:
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:

Answered by : iProgram  

Please leave any comments here within the next seven days.


Roshan Davis
EE Cleanup Volunteer
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Train for your Pen Testing Engineer Certification

Enroll today in this bundle of courses to gain experience in the logistics of pen testing, Linux fundamentals, vulnerability assessments, detecting live systems, and more! This series, valued at $3,000, is free for Premium members, Team Accounts, and Qualified Experts.

Tackle projects and never again get stuck behind a technical roadblock.
Join Now