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# Draw perpendicular lines

Posted on 2004-04-15
Medium Priority
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I need to draw perpendicular lines between two parallel lines .The perpendicular lines have to be drawn with constant distance between them .Two parallel lines could be straight lines or with slope. Known:  begin and end points for two parallel lines.

Thank you.
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Question by:shean85
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LVL 4

Expert Comment

ID: 10836246
Here I coded some part of what you want and I think you continue with this:

CPaintDC dc(this);
CPoint pt11( 10, 10 );
CPoint pt12( 100, 100 );
CPoint pt21( 10, 60 );
CPoint pt22( 100, 150 );

dc.MoveTo( pt11 );
dc.LineTo( pt12 );
dc.MoveTo( pt21 );
dc.LineTo( pt22 );

float m = (float)(pt12.y - pt11.y) / (float)(pt12.x - pt11.y);
float alpha = ::atanf( m );
float palpha = alpha + (3.14159f/2.0f);

CPoint basePt;

basePt.x = (pt12.x - pt11.x) / 2;
basePt.y = (pt12.y - pt11.y) / 2;

CPoint pbasePt;
int len = 50;

pbasePt.x = basePt.x + (int)(len * ::cos( palpha ));
pbasePt.y = basePt.y + (int)(len * ::sin( palpha ));

dc.MoveTo( basePt );
dc.LineTo( pbasePt );

0

LVL 6

Accepted Solution

joghurt earned 600 total points
ID: 10836319
Though this sounds as a school assignment, we try to give you some help.

* Mathematical background:
Do you know how to calculate the direction of original line(s)?
Do you know how to calculate the direction of the perpendicular lines?
Do you know how to calculate points on the original line(s)?
Do you know how to move a given distance along the original line(s)?

* Programming background:
Do you know how to draw lines in WinAPI (or in MFC)?
0

LVL 4

Expert Comment

ID: 10837701
Though this sounds sarcastic :

Does (s)he have to know?
What's this site for?

(S)he asks for help, because (s)he doesn't know those your counted, or because (s)he is lost in even some radial-degree conversation, or because (s)he wants to have it instead of coding this thing...

Does not matter that much... so, please behave!
0

LVL 6

Expert Comment

ID: 10845389
I just wanted to make things clear. I agree this site is for helping people but it would be nice to know whether he/she stuck in a particular problem in an almost complete program or if we have to explain things from 1+1 being 2.

And you know EE's policy about helping in school assignments. We SHOULDN'T write the whole thing instead of him/her. However, we will gladly help/him in solving any particular troubles or to outline the algorithm, etc.
0

LVL 4

Expert Comment

ID: 10848075
Sure man, that's why I gave a hint, but not the whole code..

Cheers,

Caner
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