class Terrain implements Drawable {
 
   int[][] points;
  
   Terrain() {
     reset();
   }
  
   void addPoint(int x, int y) {
      if (points.length > 0) {
          x = constrain(x, points[points.length - 1][0]+1, scene.WIDTH);
      }
     
      int[] point = {x, constrain(y, (scene.HEIGHT / 4), scene.HEIGHT-1) };
      points = (int[][]) append(points, point); 
   }
   
   int heightAt(int x) {
      float d = 0;
      
      if(points.length == 4) return scene.HEIGHT / 4;
  
       
      for(int i = 2; i < points.length-1; i++) {
         
        if(points[i][0] <= x && points[i+1][0] > x) {
          
         if(points[i][0] == x || points[i][1] == points[i+1][1]) return scene.HEIGHT - points[i][1];
          
          d = int( (plane.posX - points[i][0]) / (points[i+1][0] - points[i][0]) * (points[i][1] - points[i+1][1]) );
          
          return int(scene.HEIGHT - points[i][1] + d);
        }
        
      } 
      
      return 0;
   }
   
   void reset() {      
     points = new int[0][2]; 
     
     
     int[] point0 = { scene.WIDTH, scene.HEIGHT - scene.HEIGHT / 4 };
     points = (int[][]) append(points, point0); 
     
     int[] point1 = { scene.WIDTH, scene.HEIGHT };
     points = (int[][]) append(points, point1); 
     
     int[] point2 = { 0, scene.HEIGHT };
     points = (int[][]) append(points, point2); 
     
     int[] point3 = { 0, scene.HEIGHT - scene.HEIGHT / 4 };
     points = (int[][]) append(points, point3); 
   }
  
   void draw() {
     fill(74, 152, 45);    
     
     beginShape();   
     
       for(int i = 0; i < points.length; i++) {
         vertex(points[i][0], points[i][1]); 
       }
     endShape(CLOSE);
   }
}