Jump to content

View more

Image of the Day

The night is still, but the invasion brings chaos. #screenshotsaturday #hanako #indiegame #gameart #ue4 #samurai https://t.co/cgILXuokoS
IOTD | Top Screenshots

The latest, straight to your Inbox.

Subscribe to GameDev.net Direct to receive the latest updates and exclusive content.


Sign up now

Separating axis theorem

4: Adsense

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.


  • You cannot reply to this topic
3 replies to this topic

#1 razaron   Members   

101
Like
0Likes
Like

Posted 23 January 2012 - 10:04 AM

I'm having trouble implementing the separating axis theorem. If I do the calculation in the code on paper it works, however if I run the code it doesn't.

The aabb part is for (later) optimization.

Here are the relevant bits of code:
Projection Class,
public class Projection {
protected double min;
protected double max;

public Projection(double min, double max){
  min=this.min;
  max=this.max;
}

public boolean overlap(Projection p2){
  boolean temp=true;

  if(min>p2.max || max<p2.min)
   temp=false;

  return temp;
}
}

Collision Detection part of the polygon (convex) class,
		public boolean collides(Polygon poly){
		boolean check = true;
		double temp=0;
		Projection p1;
		Projection p2;
		Point2D.Double axis;
		
		for(int i=0;i<edges;i++){
			if(check){
				double min=0,max=0;
				double dx=edge[i].v2.pos.x - edge[i].v1.pos.x;
				double dy=edge[i].v2.pos.y - edge[i].v1.pos.y;
				
				double x=(dx)/Math.sqrt(Math.pow(dx, 2) + Math.pow(dy, 2));
				double y=(dy)/Math.sqrt(Math.pow(dx, 2) + Math.pow(dy, 2));
				axis = new Point2D.Double(-x, y);
				
				min = max = (axis.x*vertex[0].pos.x)+(axis.y*vertex[0].pos.y);
				
				//project this shape
				for(int j=0;j<vertices;j++){
					temp= (axis.x*vertex[j].pos.x)+(axis.y*vertex[j].pos.y);
					if(temp<min)
						min=temp;
					if(temp>max)
						max=temp;
				}
				p1 = new Projection(min,max);
				
				
				min = max = (axis.x*poly.vertex[0].pos.x)+(axis.y*poly.vertex[0].pos.y);
				//project other shape
				for(int j=0;j<poly.vertices;j++){
					temp= (axis.x*poly.vertex[j].pos.x)+(axis.y*poly.vertex[j].pos.y);
					if(temp<min)
						min=temp;
					if(temp>max)
						max=temp;
				}
				p2 = new Projection(min,max);
				
				if(!p1.overlap(p2))
					check=false;
			}
		}
		
		return check;
	}

The implementation in the main class (done every frame),
				polygon.elementAt(j).aabbCollision=false;
				polygon.elementAt(j).polyCollision=false;
				for(int l=0;l<polygon.capacity();l++){
					if(l!=j){
						if(polygon.elementAt(j).box.compareAABB(polygon.elementAt(l).box)){
							polygon.elementAt(j).aabbCollision=true;
						}
						if(polygon.elementAt(j).collides(polygon.elementAt(l))){
							if(polygon.elementAt(l).collides(polygon.elementAt(j))){
								polygon.elementAt(j).polyCollision=true;
							}
						}
					}
				}


#2 Infernal-rk   Members   

135
Like
1Likes
Like

Posted 26 January 2012 - 05:23 PM

public Projection(double min, double max){
min
=this.min;
max
=this.max;
}


seems backwards. shouldn't it be: this.min = min; no?

#3 Pontus Palmenäs   Members   

100
Like
0Likes
Like

Posted 27 January 2012 - 07:58 AM

public Projection(double min, double max){
min=this.min;
max=this.max;
}


seems backwards. shouldn't it be: this.min = min; no?


That's where the debugger comes in handy :)

#4 razaron   Members   

101
Like
0Likes
Like

Posted 27 January 2012 - 03:10 PM

public Projection(double min, double max){
min=this.min;
max=this.max;
}


seems backwards. shouldn't it be: this.min = min; no?

You Sir, are a gentleman and a scholar.




Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.