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Posted on 1999-01-01
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Last Modified: 2013-11-20
I have a dialog box that I would like to draw circles all over, something like a screen saver, but smaller.  I can't figure out how to draw a simple circle tho!  What is the deal?  How do I draw a circle?
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Question by:abc021397
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by:thresher_shark
Comment Utility
To draw a circle, you want to use the CDC::Ellipse function.  If you have any questions on how to use it, please feel free to ask.

You can also use the API function Ellipse where you provide it a handle to a device context.
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Answers2000 earned 200 total points
Comment Utility
1. Go the dialog class source file

2. Press Ctrl-W to bring up class wiz

3. Double click on WM_PAINT in RHS list box (make sure the dialog name is selected in LHS list).  Press Edit Code

You should see

code like

void CMyDialog::OnPaint()
{
      CPaintDC dc(this); // device context for painting
      
      // Do not call CDialog::OnPaint() for painting messages
}

4. Replace the // Do not call...etc comment with your painting code.

5. To draw circles use the CDC class member (CDC is base class for CPaintDC) Ellipse as thresher says

example:

cdc.Ellipse( 0, 0, 100, 100 ) ;

The first 2 parameters are the x,y coord of the top left of rectangle containing the ellipse (0,0 is top left of the dialog).  The 3rd and 4th parameters are width and height of the box containing the ellipse.   Making the 3rd and 4th parameters the same makes the box into a square, and the ellipse into a circle.

The coord are measured in pixels (the dots making up your screen), so it may not appear exactly circular if you have a screen with non-square pixels.  You can adjust the width/height separately rto give circular appearance.

More in comment below..



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by:Answers2000
Comment Utility
6. The ellipse fills in the circle with the current brush, and draws the edge in the current pen.  By default (a white brush for the interior, and a single pixel black pen for the edge).

Change the edge by creating and selecting a different pen, e.g. CreatePen the SelectObject

Change the interior by creating and selecting a different brush, e.g. CreateSolidBrush then SelectObject

You can also use stock pens and stock brushes.e.g. GetStockObject

If you create a pen or brush with API (not MFC functions) (as opposed to using a stock one) you must also DeleteObject it when done.

Here's code to use a red pen, and a blue brush

// create pens and brushes
CPen pen ;
CBrush brush ;
pen.CreatePen( PS_SOLID, 1, RGB(255,0,0) ) ;
CPen * poldpen = dc.SelectObject( &pen ) ;
brush.CreateSolidBrush( RGB(0,0,255) ) ;
CBrush * poldbrush = dc.SelectObject( &brush ) ;

// draw circle
dc.Ellipse( 0,0,100,100 ) ;

// restore brushes
dc.SelectObject( poldbrush ) ;
dc.SelectObject( poldpen ) ;



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Expert Comment

by:Answers2000
Comment Utility
Here's code to use a red pen, and a NULL (i.e. leave alone the interior) brush

         // create pens and brushes
         CPen pen ;
         CBrush * pbrush ;
         pen.CreatePen( PS_SOLID, 1, RGB(255,0,0) ) ;
         CPen * poldpen = dc.SelectObject( &pen ) ;
         pbrush = CBrush::FromHandle( (HBRUSH)GetStockObject(NULL_BRUSH) ) ;
         CBrush * poldbrush = dc.SelectObject( pbrush ) ;

         // draw circle
         dc.Ellipse( 0,0,100,100 ) ;

         // restore brushes
         dc.SelectObject( poldbrush ) ;
         dc.SelectObject( poldpen ) ;
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