Line/Point Collsion?

Java 2D
#1

I am working on a game that’s similar to Missile Command (in fact, it was supposed to be Missile Command, but I got stuck in a loop that wouldn’t let me do anything else until the missile was done being drawn, and I’d have to re-do the whole game to fix that and I don’t have time. If anyone wants to help me with that instead, that’d be awesome :P). Essentially, you click and a line appears, and everything that runs into it blows up. I’m not exactly sure how to do the collision there, because you need to follow up the slope of the line and I find the slope by y2-y1/x2-x1. By the end, the whole slope is found, but I’m not sure how to have it actually know where the line is, as opposed to a box with the line in it.

Here’s my draw method:


      public void draw(int _x3,int x, int y, Graphics g)
{
            double x3=(double)_x3;
            MissileCommand Commander = new MissileCommand();
            Graphics2D g2D=(Graphics2D)g;
            if(x>=x3)
            {
                  m=((double)y/((double)x-x3)); //I have to parse it to a double for a true fraction.
                  System.out.println("Slope: "+m+"X change?: "+x);
                  double m2=m;
            //      m+=100;
                  x2=x3+1;
                  x+=x3;
                  while(m<=y && x2<=x )
                  {
                        //System.out.println("Slope: "+m+", "+m2+"\nX value: "+x+"\nY value: "+y);
                        Shape liney = new Line2D.Double(x3,0,x2,m); //I draw to a double. Yay²! I saved Seth from having to do an algorithm.
                        g2D.draw(liney);
                        Commander.delay();
                        x2++;
                        m+=m2;
                        System.out.println("Far: "+Far);
                  }
                  x-=x3;
            }

            if(x><x3)             {
                  m=(Math.abs((double)y/((double)x-x3))); if(m==0) m++;
                  double m2=m; //      m+=100; x2=x3; //      x+=100; while(m><=y && x2>=x)
                  {
                        //system.out.println("slope: "+m+", "+m2+"\nx value: "+x+"\ny value: "+y);
                        shape liney = new line2d.double(x3,0,x2,m);
                        g2d.draw(liney);
                        commander.delay();
                        //repaint();
                        x2--;
                        m+=m2;
                        system.out.println("other far: "+far);
                  }
            }
      }

any help would be greatly appreciated, thanks.>

#2

http://java.sun.com/j2se/1.5.0/docs/api/java/awt/geom/Line2D.html

intersects()

#3

Wow, I feel dumb. Especially because I use Line2D in my method.
Thanks so much though, I appreciate it.

Although, that is a boolean. I need the coordinate value of where it happens. Is there a way to get that?

#4

Is there a way to get that?

From that method? No.

Well, the changes between the frames are pretty small. I guess it’s hard to spot the difference. I mean we’re talking about 1-2 pixels here.

You could do that stuff with vector math. Basically you need to find the spot were those two linear graphs intersect. (Math from 8th grade is enough for that. Try to remember that stuff ;))

#5

I used a different method and got it, ptLineDist.

Thank you so much for pointing me there, you have no idea how awesome it is. I had so much done, but that wouldn’t work, so it wasn’t even a game. Thank you thank you thank you!

I did see an open-source Missile Command that used Vectors, but I wasn’t sure how it worked and I really didn’t have time to tear down my program and re-work it. Otherwise, I’d have done that instead.