line.js

function Line(x1, y1, x2, y2){
    this.x = 0;
    this.y = 0;
    this.x1 = x1||0;
    this.y1 = y1||0;
    this.x2 = x2||0;
    this.y2 = y2||0;
    this.rotation = 0;
    this.scaleX = 1;
    this.scaleY = 1;
    this.lineWidth = 1;
}

Line.prototype.draw = function(context){
    context.save();
    context.translate(this.x, this.y);
    context.rotate(this.rotation);
    context.scale(this.scaleX, this.scaleY);
    context.lineWidth = this.lineWidth;
    context.beginPath();
    context.moveTo(this.x1, this.y1);
    context.lineTo(this.x2, this.y2);
    context.closePath();
    context.stroke();
    context.restore();
}

Line.prototype.getBounds = function(){
    if(this.rotation === 0){
        var minX = Math.min(this.x1, this.x2),
            minY = Math.min(this.y1, this.y2),
            maxX = Math.max(this.x1, this.x2),
            maxY = Math.max(this.y1, this.y2);
        
        return {
            x: this.x + minX,
            y: this.y + minY,
            width: maxX - minX,
            height: maxY - minY
        };
    }else{
        var sin = Math.sin(this.rotation),
            cos = Math.cos(this.rotation),
            x1r = cos*this.x1 + sin*this.y1,
            x2r = cos*this.x2 + sin*this.y2,
            y1r = cos*this.y1 + sin*this.x1,
            y2r = cos*this.y2 + sin*this.x2;
        
        return {
            x: this.x + Math.min(x1r, x2r),
            y: this.y + Math.min(y1r, y2r),
            width: Math.max(x1r, x2r) - Math.min(x1r, x2r),
            height: Math.max(y1r, y2r) - Math.min(y1r, y2r)
        }; 
    }
}