Line of sight

Source

/* @pjs preload="player.png"; */

PImage player;

int NUMBER_OF_WALLS = 4;
int NUMBER_OF_PEOPLE = 6;

PVector[] people;
Rectangle[] walls;

// Setup the example
void setup(){
  size(640, 480);
  
  imageMode(CENTER);
  
  player = loadImage("player.png");
  
  walls = new Rectangle[NUMBER_OF_WALLS];
  for(int i = 0; i < walls.length; i++){
    int x = i * width / walls.length + 50;
    int y = floor(random(50, height-200));
    walls[i] = new Rectangle(x, y, 100, 100);
  }
  
  people = new PVector[NUMBER_OF_PEOPLE];
  
  for(int i = 0; i < people.length; i++){
    int x = floor(random(32, width-32));
    int y = floor(random(32, height-32));
    
    for(Rectangle wall : walls){
      while(wall.overlap(x, y, player.width, player.height)){
        y += 64;
      }
    }
    
    people[i] = new PVector(x, y);
  }
}

// The draw() method is called every frame
void draw(){
  background(#4488cc);
  
  PVector mV = new PVector(mouseX, mouseY);
  
  for(Rectangle wall : walls){
    wall.display();
  }
  
  for(PVector person : people){
    PVector intersect = getWallIntersection(person, mV);

    if(intersect != null){
      tint(#ff0000);
    }else{
      noTint();
      stroke(255);
      line(person.x, person.y, mV.x, mV.y);
    }
    
    image(player, person.x, person.y);
  }
  
  ellipse(mV.x, mV.y, 32, 32);
}

PVector getWallIntersection(PVector start, PVector end){
  float distanceToWall = MAX_FLOAT;
  PVector closestIntersection = null;
  
  for(Rectangle wall : walls){
    PVector nw, ne, se, sw, intersect;
    nw = new PVector(wall.x, wall.y);
    ne = new PVector(wall.x + wall.width, wall.y);
    sw = new PVector(wall.x, wall.y + wall.height);
    se = new PVector(wall.x + wall.width, wall.y + wall.height);
    
    /* top line */
    intersect = intersectPLines(start, end, nw, ne);
    if(intersect != null){
      float distance = dist(start.x, start.y, intersect.x, intersect.y);
      if(distance < distanceToWall){
        distanceToWall = distance;
        closestIntersection = intersect;
      }
    }
    
    /* left line */
    intersect = intersectPLines(start, end, nw, sw);
    if(intersect != null){
      float distance = dist(start.x, start.y, intersect.x, intersect.y);
      if(distance < distanceToWall){
        distanceToWall = distance;
        closestIntersection = intersect;
      }
    }
    
    /* right line */
    intersect = intersectPLines(start, end, se, ne);
    if(intersect != null){
      float distance = dist(start.x, start.y, intersect.x, intersect.y);
      if(distance < distanceToWall){
        distanceToWall = distance;
        closestIntersection = intersect;
      }
    }
    
    /* bottom line */
    intersect = intersectPLines(start, end, se, sw);
    if(intersect != null){
      float distance = dist(start.x, start.y, intersect.x, intersect.y);
      if(distance < distanceToWall){
        distanceToWall = distance;
        closestIntersection = intersect;
      }
    }
  }
  return closestIntersection;
}

PVector intersectPLines(PVector v1start, PVector v1end, PVector v2start, PVector v2end){
  return intersectLines(v1start.x, v1start.y, v1end.x, v1end.y, v2start.x, v2start.y, v2end.x, v2end.y);
}

/* From: http://processingjs.org/learning/custom/intersect/ */
PVector intersectLines(float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4){
  float a1, a2, b1, b2, c1, c2;
  float r1, r2 , r3, r4;
  float denom, offset, num;
  
  PVector ret = null;

  // Compute a1, b1, c1, where line joining points 1 and 2
  // is "a1 x + b1 y + c1 = 0".
  a1 = y2 - y1;
  b1 = x1 - x2;
  c1 = (x2 * y1) - (x1 * y2);

  // Compute r3 and r4.
  r3 = ((a1 * x3) + (b1 * y3) + c1);
  r4 = ((a1 * x4) + (b1 * y4) + c1);

  // Check signs of r3 and r4. If both point 3 and point 4 lie on
  // same side of line 1, the line segments do not intersect.
  if ((r3 != 0) && (r4 != 0) && same_sign(r3, r4)){
    return null;
  }

  // Compute a2, b2, c2
  a2 = y4 - y3;
  b2 = x3 - x4;
  c2 = (x4 * y3) - (x3 * y4);

  // Compute r1 and r2
  r1 = (a2 * x1) + (b2 * y1) + c2;
  r2 = (a2 * x2) + (b2 * y2) + c2;

  // Check signs of r1 and r2. If both point 1 and point 2 lie
  // on same side of second line segment, the line segments do
  // not intersect.
  if ((r1 != 0) && (r2 != 0) && (same_sign(r1, r2))){
    return null;
  }

  //Line segments intersect: compute intersection point.
  denom = (a1 * b2) - (a2 * b1);

  if (denom == 0) {
    return null;
  }

  if (denom < 0){ 
    offset = -denom / 2; 
  } 
  else {
    offset = denom / 2 ;
  }

  // The denom/2 is to get rounding instead of truncating. It
  // is added or subtracted to the numerator, depending upon the
  // sign of the numerator.
  num = (b1 * c2) - (b2 * c1);
  
  ret = new PVector(0,0);
  
  if (num < 0){
    ret.x = (num - offset) / denom;
  } 
  else {
    ret.x = (num + offset) / denom;
  }

  num = (a2 * c1) - (a1 * c2);
  if (num < 0){
    ret.y = ( num - offset) / denom;
  } 
  else {
    ret.y = (num + offset) / denom;
  }
  // lines_intersect
  return ret;
}


boolean same_sign(float a, float b){
  return (( a * b) >= 0);
}

class Rectangle{
  int x;
  int y;
  int width;
  int height;
  Rectangle(int x, int y, int width, int height){
    this.x = x;
    this.y = y;
    this.width = width;
    this.height = height;
  }
  void display(){
    noStroke();
    rect(x, y, width, height);
  }
  
  boolean overlap(int otherX, int otherY, int otherWidth, int otherHeight){
    return !(x + width < otherX || x > otherX+otherWidth || y + height < otherY || y > otherY+otherHeight);
  }
}