[Last Call] Learn about multicloud storage options and how to improve your company's cloud strategy. Register Now


Click and rotate?

Posted on 2000-04-05
Medium Priority
Last Modified: 2010-04-15
Ok, here is what I am trying to do. I am sure you have all played rts(real
time strategy) games, where you click on one unit, and then click on another
unit, and the first one turns toward the second, and starts walking. I am
trying to do a similar thing. What I really need help on is this. I know the
x,y location of the 2 objects, but how do I get the angle between the two? I
have tried using some stuff, but It doesn't work :-(. Could anyone put me on
the right track? I understand trig, so if you use those functions I can
follow you.
Question by:graphix_man
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
  • 2
  • +2

Expert Comment

ID: 2688803
assuming (x1,y1) is bigger than x,y
(otherwise you must use absolute values)

what I propose is the following method:
x1-x will give you the X distance between the points,
y1-y will give you the Y between the points.

now i build a right angle triangle
where one angle is 90 degrees.
and two lengths are known
to get the angles:


so just compute (x1-x)*(y1-y) into z
and you angle is either 90*z/z+1
or 90 minus that.

try to draw it out, and it'll be clearer.

Author Comment

ID: 2689634
I follow you up
=(a)/(90-a), cause I did the same thing. What does a/90-a mean? also what is a defined as?


Expert Comment

ID: 2689657
well, when you have a right angle triangle the ratio of the two sidies of the triangle is the SAME as the ratio
for the two angles, and the two angles
are x and 180-90-x which equals 90-x.
Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.


Expert Comment

ID: 2689704
If one is at X1,Y1  and the other is at X2,Y2 then you could use;

float line1, line2;
double angle;

line1 = (float)X2 - (float)X1;
line2 = (float)Y2 - (float)Y1;

angle = atan(line1/line2);


Expert Comment

ID: 2689720
Heres a console example, and remember that the angle will be in radians (not degrees).

#include <math.h>
#include <stdio.h>
#include <errno.h>

void main( void )
   double x1, x2, y;

   printf( "Enter a real number: " );
   scanf( "%lf", &x1 );
   y = atan( x1 );
   printf( "Arctangent of %f: %f\n", x1, y );
   printf( "Enter a second real number: " );
   scanf( "%lf", &x2 );
   y = atan2( x1, x2 );
   printf( "Arctangent of %f / %f: %f\n", x1, x2, y );

Expert Comment

ID: 2691302
sorry if i'm trying to say something that already have been said

object 1:(x1,y1)
object 2:(x2,y2)

i"ll give a math formula
x=|x1-x2|//modul i mean it have to be >0
y=|y1-y2|//modul i mean it have to be >0

don't forget to use float's or casting to floats that you won't get your numbers rounded

Author Comment

ID: 2694014
I have this code:
            float tantest;

            double test=atan(tantest);
That I got from looking at the posts. Is this correct, in that is spits out the angle between the 2 points? If so I think 3drich gets the points. If not whoever can fix this up wins.
LVL 84

Expert Comment

ID: 2694200
Why are you taking the absolute value of xmatrix and ymatrix?  What do you mean by "angle between the 2 points"?

Accepted Solution

3rsrichard earned 150 total points
ID: 2694652
What you have is OK.
You don't need to use only positive values, atan works for negative as well.

You need to consider that point 2 could be right/left or up/down from point 1.

#include <math.h>
#include <stdio.h>
#include <errno.h>

void main( void )
   double x, y, angle;

   printf( "Enter a real number x: " );
   scanf( "%lf", &x );
   printf( "Enter a second real number y: " );
   scanf( "%lf", &y );
   angle = atan2( x, y );
   printf( "Arctangent of %f / %f: %f\n", x, y, angle );

   printf( "Arctangent of %f / %f: %f\n", x, y, (angle*180/3.14159) );



Featured Post

What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Summary: This tutorial covers some basics of pointer, pointer arithmetic and function pointer. What is a pointer: A pointer is a variable which holds an address. This address might be address of another variable/address of devices/address of fu…
Examines three attack vectors, specifically, the different types of malware used in malicious attacks, web application attacks, and finally, network based attacks.  Concludes by examining the means of securing and protecting critical systems and inf…
The goal of this video is to provide viewers with basic examples to understand and use pointers in the C programming language.
The goal of this video is to provide viewers with basic examples to understand how to use strings and some functions related to them in the C programming language.

650 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question