How to draw multiple lines dynamically using OnDraw function.

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Im Creating SDI application to draw the lines when the user press and release the mouse button. I given moveto and lineto within the OnDraw function to make the lines present even when the window is resized. I used Invalidate() in the OnLButtonUp function it invalidates the entire client area. To draw multiple lines it doesn't work. Here is my code..

C++

void CserializationTestView::OnLButtonDown(UINT nFlags, CPoint point)
{
	// TODO: Add your message handler code here and/or call default
	l[0]=point.x;
	l[1]=point.y;
	CView::OnLButtonDown(nFlags, point);
}

void CserializationTestView::OnLButtonUp(UINT nFlags, CPoint point)
{
	// TODO: Add your message handler code here and/or call default
	CClientDC dc(this);
	PtLine=CPoint(point.x,point.y);
	Invalidate();
	CView::OnLButtonUp(nFlags, point);
}

void CserializationTestView::OnDraw(CDC* pDC)
{
	CserializationTestDoc* pDoc = GetDocument();
	ASSERT_VALID(pDoc);
	pDC->MoveTo(l[0],l[1]);
	pDC->LineTo(PtLine);
	
	// TODO: add draw code for native data here
}

To draw multiple lines what i have to do.

Posted 9-Dec-12 20:20pm

J.Surjith Kumar

Updated 9-Dec-12 20:44pm

Mohibur Rashid

v3

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Mohibur Rashid · Answer 1 · 2012-12-09T20:49:00

Solution 1

You will have to remember all the points and then every time ondraw is being called it will use the stored values to draw lines.

You can use vector to store all your clicked points. It would be best practice if you just use vector to store your data

C++

 //a simple working example
void CserializationTestView::OnDraw(CDC* pDC)
{
	CappDoc* pDoc = GetDocument();
	ASSERT_VALID(pDoc);
	if (!pDoc)
		return;
	// TODO: add draw code for native data here
	for(std::vector<CCoords>::iterator it=list.begin();it!=list.end();++it)
	{
		pDC->MoveTo(it->start);
		pDC->LineTo(it->End);
	}
	
}
void CserializationTestView::OnLButtonUp(UINT nFlags, CPoint point)
{
	list[list.size()-1].End=point;
	Invalidate();
}
void CserializationTestView::OnLButtonDown(UINT nFlags, CPoint point)
{
	
	CCoords nlist;
	nlist.start=point;
	list.push_back(nlist);
}
//definition of CCoords
class CCoords
{
public:
	CPoint start;
	CPoint End;
};

Posted 9-Dec-12 20:49pm

Mohibur Rashid

Updated 10-Dec-12 14:11pm

v2

Comments

J.Surjith Kumar 10-Dec-12 3:11am

will u give me some practical example.

Mohibur Rashid 10-Dec-12 3:15am

Of what?

Mohibur Rashid 10-Dec-12 21:38pm

Please recheck the answer for example

J.Surjith Kumar 11-Dec-12 0:28am

It shows an error as undeclared it,iteration,list and vector.

Mohibur Rashid 11-Dec-12 0:44am

include vector header file
e.g.
#include <vector>

read about vector too

J.Surjith Kumar 11-Dec-12 1:55am

ok finally it shows only list as undeclared

J.Surjith Kumar 11-Dec-12 1:57am

ok now it shows only list is undeclared.

J.Surjith Kumar 11-Dec-12 2:08am

atlast it shows the only error C2248: 'CObject::CObject' : cannot access private member declared in class 'CObject'

Mohibur Rashid 11-Dec-12 4:44am

#include <vector>

J.Surjith Kumar 11-Dec-12 4:48am

i included this header

J.Surjith Kumar 10-Dec-12 3:20am

I used Invalidate() in the OnLButtonUp() function which invalidates the entire client area for every time it has been called. So that i cant draw multiple lines for that i need a solution.

Richard MacCutchan 10-Dec-12 4:52am

You need to hold a list of all the lines (or points) in your drawing, and then redraw all the lines from those points in your OnDraw() function. Also note that you cannot use the same array elements to hold different points. I was sure I had explained this already, but perhaps someone else is working on the exact same problem.

Richard MacCutchan 10-Dec-12 4:58am

Is this question anything to do with you?

J.Surjith Kumar 10-Dec-12 5:16am

Have u given any example code anywhere regarding this issues.

J.Surjith Kumar 10-Dec-12 5:29am

If i give Invalidate(FALSE) in the OnLButtonUp function. Multiple lines can be drawn but when i resize the window the lines which is drawn last is only shown.

JackDingler 10-Dec-12 12:53pm

You keep making the same comments over and over, and the answers will be the same.

You need to keep a list of the lines you wish to draw. There is no magic going on in the background that reads your mind to figure out what to draw and what not to draw.

When you call an Invalidate(FALSE), you're simply triggering a paint w/o a background erase. When you resize, a background erase occurs automatically.

In your OnDraw / OnPaint, you need to walk through your list of lines and draw each one. Your mouse functions should simply update your list of lines.