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Drawing and deleting lines

Posted on 2000-03-17
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Last Modified: 2013-11-20
Hi,

I made the following code. It should Draw lines with black color, if lDel is FALSE, if lDel is FALSE, it should delete this lines by setting the line-colour to the background-colour, so that the already drawn lines are overdrawn by the background-colour. But - that doesn´t work. How does it work the right way? Please give a detailed answer! Thanks in advance!


COLORREF BkColor, FgColor;

if (lDel)      // Set backgroundcolor
{      FgColor = dc->GetTextColor();
      BkColor = dc->GetBkColor();
      dc->SetTextColor(BkColor);
}

// Now I draw or delete some lines
...

if (lDel)      // Set old line-color as the new linecolor
{      dc->SetTextColor(FgColor);
}
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Question by:erebel
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2 Comments
 
LVL 12

Expert Comment

by:migel
ID: 2629708
Hi!
When you Draw line DC use PEN currently selected to it, so lines always appear in PEN`s color, not setted by SetTextColor functions.
Best way to erase lines is using XOR mode while drawing
to do it you must call SetROP2 with R2_XORPEN;
line will be erased when you draw it next time.
0
 
LVL 3

Accepted Solution

by:
kulina earned 150 total points
ID: 2654484
In OnPaint enter these lines
// start
CPen pen;
CPaintDC dc(this);
// Don't forget to do this...
CPen* pOldPen = dc.SelectObject (&pen);
if(IDel == FALSE)
{
BkColor = dc->GetBkColor();
pen.CreatePen(PS_SOLID, 1, BkColor );
dc.SelectObject(&pen);
dc.MoveTo(x, y);
dc.LineTo(a, b);
}
dc.SelectObject(pOldPen);
// end

....where x and y are coordinates starting postition of your line, and a and b are ending positions of your line.
I haven't tried this possible solution but I'm pretty convicned it'll work.
Good Luck!
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