objects.js

function Ball(x, y, dx, dy) {
    this.x = x;
    this.y = y;
    this.dx = dx;
    this.nom_dy = dy;
    this.dy = dy;
    this.r = 5;

    this.draw = function (context) {
        var oldstroke = context.strokeStyle;

        context.beginPath();
        context.moveTo(this.x+this.r, this.y);
        context.arc(this.x, this.y, this.r, 0, 2*Math.PI);
        context.stroke();

        context.strokeStyle = oldstroke;
    }

    this.update = function () {
        this.x += this.dx;
        this.y += this.dy;
    }

    this.applyGravity = function () {
        this.dy += gravity;
    }

    this.isNowDead = function (scene) {
        if (this.x > scene.width || this.x < 0) return true;
        if (this.y > scene.height) return true;
        return false;
    }

    this.bounceOffLine = function(line) {
        // To find normal, get vector of line segment, swap x and y and negate y
        // Get vector of line segment with magnitude one by dividing by hypot, or length
        var nx = (line.y2 - line.y1) / line.length;
        var ny = -(line.x2 - line.x1) / line.length;

        // Complicated calculation for reflection of vector (ball velocity) across arbitrary line
        // v' = v - 2 * dot(v, N) * N
        var dot = (this.dx * nx + this.dy * ny);
        this.dx = this.dx - 2 * dot * nx;
        this.dy = this.dy - 2 * dot * ny;
    }

    this.intersects = function (line) {
        // distance from point to line formula, derived by dot product line to point vector against line's normal direction vector
        var d =  line.ay * this.x -  line.ax * this.y + line.x2y1y2x1;
        d = d / line.length;

        var e = line.ay * (this.x + this.dx) - line.ax * (this.y+this.dy) + line.x2y1y2x1;
        e = e / line.length;

        if (Math.abs(d) <= this.r || d * e < 0) { /* d*e < 0 if signs are different */
            // ball is close to line, now check if within bounds of line *segment*

            var bx = (this.x - line.x1);
            var by = (this.y - line.y1);

            var cx = (this.x - line.x2);
            var cy = (this.y - line.y2);

            var adotb = line.ax*bx + line.ay*by;
            var adotc = line.ax*cx + line.ay*cy;

            if (adotb > 0 && adotc < 0) return true;
            return false;
        }
        return false;
    }
}

function Dropper(x, y, interval, scene) {
    this.x = x;
    this.y = y;
    this.r = 5;
    this.interval = interval;
    this.scene = scene;
    this.timer = null;

    this.draw = function (context) {
        var oldstroke = context.strokeStyle;

        context.beginPath();
        context.moveTo(this.x+this.r, this.y);
        context.arc(this.x, this.y, this.r, 0, 2*Math.PI);
        context.stroke();

        context.strokeStyle = oldstroke;
    }

    this.dropBall = function (scene) {
       this.scene.balls[this.scene.balls.length] = new Ball(this.x, this.y, 0, 0);
    }

    this.start = function () {
        var self = this;
        this.timer = setInterval(function () { self.dropBall(self.scene); }, this.interval);
    }

    this.stop = function () {
        clearInterval(this.timer);
    }

    this.start();
}

function Line(x1, y1, x2, y2) {
    this.BASE_COLOR = '#0000FF';
    this.x1 = x1;
    this.x2 = x2;
    this.y1 = y1;
    this.y2 = y2;
    this.r = 3;
    this.max = canvas.width;
    this.min = 1;
    this.color = this.BASE_COLOR;

    this.recompute = function() {
        // Precomputed values
        this.length = Math.sqrt(Math.pow(this.x2-this.x1, 2) + Math.pow(this.y2-this.y1, 2));
        this.x2y1y2x1 = this.x2 * this.y1 - this.y2 * this.x1;
        this.ax = (this.x2 - this.x1);
        this.ay = (this.y2 - this.y1);
    }
    this.recompute();

    this.draw = function (context) {
        var oldstroke = context.strokeStyle;

        context.beginPath();
        context.strokeStyle = this.color;
        context.moveTo(this.x1+this.r, this.y1);
        context.arc(this.x1, this.y1, this.r, 0, 2*Math.PI);
        context.moveTo(this.x1, this.y1);
        context.lineTo(this.x2, this.y2);
        context.moveTo(this.x2+this.r, this.y2);
        context.arc(this.x2, this.y2, this.r, 0, 2*Math.PI);
        context.stroke();

        context.strokeStyle = oldstroke;
    }

    this.ding = function () {
        var count = 8;
        var index = count - Math.ceil(this.length / (this.max-this.min) * count);
        sound.play(""+index);
    }
}

var intersects = function (x, y, line, dist) {
    // distance from point to line formula, derived by dot product line to point vector against line's normal direction vector
    var d =  line.ay * x -  line.ax * y + line.x2y1y2x1;
    d = Math.abs(d / line.length);

    if (d <= dist) {
        // ball is close to line, now check if within bounds of line *segment*

        var bx = (x - line.x1);
        var by = (y - line.y1);

        var cx = (x - line.x2);
        var cy = (y - line.y2);

        var adotb = line.ax*bx + line.ay*by;
        var adotc = line.ax*cx + line.ay*cy;

        if (adotb > 0 && adotc < 0) return true;
        return false;
    }
    return false;
}