LineRect.pde

/*
LINE/RECTANGLE
 Jeff Thompson | 2015 | www.jeffreythompson.org
 
 */

float x1 = 0;      // points for line (controlled by mouse)
float y1 = 0;
float x2 = 20;     // static point
float y2 = 20;

float sx = 200;    // square position
float sy = 100;
float sw = 200;    // and size
float sh = 200;


void setup() {
  size(600, 400);

  strokeWeight(5);  // make the line easier to see
}


void draw() {
  background(255);
  
  // set end of line to mouse coordinates
  x1 = mouseX;
  y1 = mouseY;

  // check if line has hit the square
  // if so, change the fill color
  boolean hit = lineRect(x1,y1,x2,y2, sx,sy,sw,sh);
  if (hit) fill(255,150,0);
  else fill(0,150,255);
  noStroke();
  rect(sx, sy, sw, sh);

  // draw the line
  stroke(0, 150);
  line(x1, y1, x2, y2);
}


// LINE/RECTANGLE
boolean lineRect(float x1, float y1, float x2, float y2, float rx, float ry, float rw, float rh) {

  // is either end INSIDE the rectangle?
  // if so, return true immediately
  boolean inside1 = pointRect(x1,y1, rx,ry,rw,rh);
  boolean inside2 = pointRect(x2,y2, rx,ry,rw,rh);
  if (inside1 || inside2) return true;
  
  // check if the line has hit any of the rectangle's sides
  // uses the Line/Line function below
  boolean left =   lineLine(x1,y1,x2,y2, rx,ry,rx, ry+rh);
  boolean right =  lineLine(x1,y1,x2,y2, rx+rw,ry, rx+rw,ry+rh);
  boolean top =    lineLine(x1,y1,x2,y2, rx,ry, rx+rw,ry);
  boolean bottom = lineLine(x1,y1,x2,y2, rx,ry+rh, rx+rw,ry+rh);
  
  // if ANY of the above are true, the line has hit the rectangle
  if (left || right || top || bottom) {
    return true;
  }
  return false;
}


// POINT/RECTANGLE
boolean pointRect(float px, float py, float rx, float ry, float rw, float rh) {
    
  // is the point inside the rectangle's bounds?
  if (px >= rx &&        // right of the left edge AND
      px <= rx + rw &&   // left of the right edge AND
      py >= ry &&        // below the top AND
      py <= ry + rh) {   // above the bottom 
        return true;
  }
  return false;
}


// LINE/LINE
boolean lineLine(float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4) {

  // calculate the direction of the lines
  float uA = ((x4-x3)*(y1-y3) - (y4-y3)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
  float uB = ((x2-x1)*(y1-y3) - (y2-y1)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));

  // if uA and uB are between 0-1, lines are colliding
  if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {

    // optionally, draw a circle where the lines meet
    float intersectionX = x1 + (uA * (x2-x1));
    float intersectionY = y1 + (uA * (y2-y1));
    fill(255,0,0);
    noStroke();
    ellipse(intersectionX, intersectionY, 20, 20);

    return true;
  }
  return false;
}