// The Nature of Code
// Daniel Shiffman
// http://natureofcode.com

// Flow Field Following

class FlowField {
    
    //A flow field is a two dimensional array of PVectors
    PVector[][] field;
    int cols, rows; // Columns and Rows
    int resolution; // How large is each "cell" of the flow field
    
    FlowField(int r) {
        resolution = r;
        // Determine the number of columns and rows based on sketch's width and height
        cols = width / resolution;
        rows = height / resolution;
        field = new PVector[cols][rows];
        init();
    }
    
    void init() {
        // Reseed noise so we get a new flow field every time
        noiseSeed((int)random(10000));
        float xoff = 0;
        for (int i = 0; i < cols; i++) {
            float yoff = 0;
            for (int j = 0; j < rows; j++) {
                float theta = map(noise(xoff,yoff),0,1,0,TWO_PI);
                // Polarto cartesian coordinate transformation to get x and y components of the vector
                field[i][j] = new PVector(cos(theta),sin(theta));
                yoff += 0.1;
            }
            xoff += 0.1;
        }
    }
    
    //Draw every vector
    void display() {
        for (int i = 0; i < cols; i++) {
            for (int j = 0; j < rows; j++) {
                drawVector(field[i][j],i * resolution,j * resolution,resolution - 2);
            }
        }
        
    }
    
    //Renders a vector object 'v' as an arrow and a position 'x,y'
    void drawVector(PVector v, float x, float y, float scayl) {
        pushMatrix();
        float arrowsize = 4;
        // Translateto position to render vector
        translate(x,y);
        stroke(0,100);
        // Call vector heading function to get direction (note that pointing to the right is a heading of 0) and rotate
        rotate(v.heading2D());
        // Calculatelength of vector & scale it to be bigger or smaller if necessary
        float len = v.mag() * scayl;
        // Draw three lines to make an arrow (draw pointing up since we've rotate to the proper direction)
        line(0,0,len,0);
        //line(len,0,len-arrowsize,+arrowsize/2);
        //line(len,0,len-arrowsize,-arrowsize/2);
        popMatrix();
    }
    
    PVector lookup(PVector lookup) {
        int column = int(constrain(lookup.x / resolution,0,cols - 1));
        int row = int(constrain(lookup.y / resolution,0,rows - 1));
        return field[column][row].get();
    }
    
    
}