Paint method flickering

Question

consider the following paint function (abbreviated):

public void paint(object sender, PaintEventArgs e)
{
    base.OnPaint(e);

    Graphics g = e.Graphics;

    BufferedGraphicsContext context = BufferedGraphicsManager.Current;
    BufferedGraphics buffer = context.Allocate(g, e.ClipRectangle);

    buffer.Graphics.Clear(Color.PaleVioletRed);

    // skip drawing if cond is true (condition is not relevant)
    if(!cond)
    {
        try
        {
          // l is some List<p>
          foreach(Point p in l)
          { 
             // ...calculate X and Y... (not relevant)

             buffer.Graphics.FillEllipse(new SolidBrush(Color.Blue), p.X,p.Y, Point.SIZE,Point.SIZE);
           }                                          
         }

         catch {} // some exception handling (not relevant)

         finally{
            buffer.Render(g);
         }
    }                
    buffer.Render(g);
}

Note that the code above is more or less pseudo-code. I hoped that using the BufferedGraphics-object, the flickering would vanish. In fact, it didn't. At first, I thought that the paint-method would take to long, which it presumably did not (I measured 4-7 ms for each call). If I set cond to true, it still flickers although the paint-method takes almost no time. It might be important that the paint-method will paint on a panel and that I am using a timer to invalidate the panel roughly every 50 ms. How can I finally eliminate the flickering?

Thanks, it is really not needed. However, the problem still exists. — Max Beikirch, Mar 03 '13 at 14:35
Your code is not eliminating the major reason for flickering, the drawing that's done by OnPaintBackground(). Do favor the built-in support for double-buffering in Winforms. Check [this answer](http://stackoverflow.com/a/3113515/17034) for a double-buffered panel. Or just use PictureBox if you don't need scrolling support, the most basic control that has double-buffering turned on by default. — Hans Passant, Mar 03 '13 at 15:08

score 2 · Accepted Answer · answered Mar 03 '13 at 13:34

2

Just try setting the property in the constructor:

this.DoubleBuffered = true;

Then you shouldn't need the BufferedGraphics stuff:

public void paint(object sender, PaintEventArgs e)
{
  base.OnPaint(e);

  Graphics g = e.Graphics;       
  g.Clear(Color.PaleVioletRed);

  // skip drawing if cond is true (condition is not relevant)
  if(!cond)
  {
    // l is some List<p>
    foreach(Point p in l)
    { 
      // ...calculate X and Y... (not relevant)  
      g.FillEllipse(new SolidBrush(Color.Blue), p.X,p.Y, Point.SIZE,Point.SIZE);
    }                                          
  }
}

answered Mar 03 '13 at 13:34

LarsTech

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Thanks for your answer. Unfortunately, the panel does not have such an property. I fear there might be a litte misunderstandment: `paint` is my event listener to onPaint, I didn't derive from Panel. – Max Beikirch Mar 03 '13 at 14:38
@MaxBeikirch Try deriving from the panel. Or you can use some reflection: [How to double buffer .NET controls on a form?](http://stackoverflow.com/a/77233/719186) – LarsTech Mar 03 '13 at 14:43
Deriving from the panel in the only solution. I hoped that I could avoid that, but sadly it does not work. Thanks for your answer! – Max Beikirch Mar 09 '13 at 20:41

Paint method flickering

1 Answers1