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  SAT collision detection and calculating MTV - slick2d  (Read 638 times)
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Offline sun

Innocent Bystander





« Posted 2012-07-15 17:19:34 »

Hi, I'm currently implementing SAT collision detection for my game using SAT, which correctly returns true when there is a collision and false when there is isn't. However, I want to extend the code to return the MTV but I'm having difficulties trying to return the correct value. Below is the code:

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   ArrayList<Vector2f> playerV = new ArrayList<Vector2f>();
   ArrayList<Vector2f> shape2V = new ArrayList<Vector2f>();

    float playerMin = 0;
    float playerMax = playerMin;
     
    float shapeMin = 0;
    float shapeMax = shapeMin;
    Vector2f shapeNormal = new Vector2f(0,0);  
   
   for(int j = playerV.size()-1, i = 0; i < playerV.size(); j = i, i++){
     
      Vector2f playerCorner1 = new Vector2f(playerV.get(j));
      Vector2f playerCorner2 = new Vector2f(playerV.get(i));
     
      Vector2f shapeCorner1 = new Vector2f(shape2V.get(j));
      Vector2f shapeCorner2 = new Vector2f(shape2V.get(i));
           
      Vector2f playerNormal = new Vector2f (playerCorner2.sub(playerCorner1).getPerpendicular().normalise());
     
      playerMin = playerV.get(0).dot(playerNormal);
      playerMax = playerMin;
     
         for(int v = 0; v < playerV.size(); v++){
               float dot = playerV.get(v).dot(playerNormal);
            if(dot < playerMin){
               playerMin = dot;
            }else if(dot > playerMax){
               playerMax = dot;
            }      
          }
     
          for(int u = 0; u < shape2V.size(); u++){
               float dot = shape2V.get(u).dot(playerNormal);
            if(dot < shapeMin){
               shapeMin = dot;
            }else if(dot > shapeMax){
               shapeMax = dot;
               }      
           }
               
            if(playerMin > shapeMax ||   shapeMin >  playerMax){
               return false;
            }else{
                                copyaxis = playerNormal;
                                }
   }
       
         mtv.set((shapeMax-playerMin) *-copyaxis.x ,(shapeMax-playerMin)*-copyaxis.y);
    return true;
   
   }


What would be the best way to calculate the MTV? This was the recourse that I had used http://rocketmandevelopment.com/2010/05/19/separation-of-axis-theorem-for-collision-detection/ , but the method used to calculate the MTV is giving odd results. The mtv returned with the method described in the article always returns  a 0 value for the x part of the mtv, for example: (0.0,59.0). This does make sense since the normalized vector for the axis being tested is something like (0,1) on collision.
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