// Inits

window.onload = function init() {

  var game = new GF();

  game.start();

};

​

​

// GAME FRAMEWORK STARTS HERE

var GF = function(){

    // Vars relative to the canvas

    var canvas, ctx, w, h; 

​

    // vars for counting frames/s, used by the measureFPS function

    var frameCount = 0;

    var lastTime;

    var fpsContainer;

    var fps; 

    // vars for handling inputs

    var inputStates = {};

    var measureFPS = function(newTime){

         // test for the very first invocation

         if(lastTime === undefined) {

           lastTime = newTime; 

           return;

         }

        //calculate the difference between last & current frame

        var diffTime = newTime - lastTime; 

​

        if (diffTime >= 1000) {

            fps = frameCount;    

            frameCount = 0;

            lastTime = newTime;

        }

​

        //and display it in an element we appended to the 

        // document in the start() function

       fpsContainer.innerHTML = 'FPS: ' + fps; 

       frameCount++;

    };

     // clears the canvas content

     function clearCanvas() {

       ctx.clearRect(0, 0, w, h);

     }

     // Functions for drawing the monster and maybe other objects

     function drawMyMonster(x, y) {

       // draw a big monster !

       // head

       // save the context

       ctx.save();

       // translate the coordinate system, draw relative to it

       ctx.translate(x, y);

       // (0, 0) is the top left corner of the monster.

       ctx.strokeRect(0, 0, 100, 100);

       // eyes

       ctx.fillRect(20, 20, 10, 10);

       ctx.fillRect(65, 20, 10, 10);

       // nose

       ctx.strokeRect(45, 40, 10, 40);

       // mouth

       ctx.strokeRect(35, 84, 30, 10);

       // teeth

       ctx.fillRect(38, 84, 10, 10);

       ctx.fillRect(52, 84, 10, 10);

      // restore the context

      ctx.restore(); 

    }

    var mainLoop = function(time){

        //main function, called each frame 

        measureFPS(time);

        // Clear the canvas

        clearCanvas();

        // draw the monster

        drawMyMonster(10+Math.random()*10, 10+Math.random()*10);

        // check inputStates

        if (inputStates.left) {

            ctx.fillText("left", 150, 20);

        }

        if (inputStates.up) {

            ctx.fillText("up", 150, 40);

        }

       if (inputStates.right) {

            ctx.fillText("right", 150, 60);

        }

        if (inputStates.down) {

            ctx.fillText("down", 150, 80);

        } 

        if (inputStates.space) {

            ctx.fillText("space bar", 140, 100);

        }

        if (inputStates.mousePos) { 

            ctx.fillText("x = " + inputStates.mousePos.x + " y = " + inputStates.mousePos.y, 5, 150);

        }

      if (inputStates.mousedown) { 

            ctx.fillText("mousedown b" + inputStates.mouseButton, 5, 180);

        }

        // call the animation loop every 1/60th of second

        requestAnimationFrame(mainLoop);

    };

​

    function getMousePos(evt) {

        // necessary to take into account CSS boudaries

        var rect = canvas.getBoundingClientRect();

        return {

            x: evt.clientX - rect.left,

            y: evt.clientY - rect.top

        };

    }

    var start = function(){

        // adds a div for displaying the fps value

        fpsContainer = document.createElement('div');

        document.body.appendChild(fpsContainer);

        // Canvas, context etc.

        canvas = document.querySelector("#myCanvas");

        // often useful

        w = canvas.width; 

        h = canvas.height;  

        // important, we will draw with this object

        ctx = canvas.getContext('2d');

        // default police for text

        ctx.font="20px Arial";

       //add the listener to the main, window object, and update the states

      window.addEventListener('keydown', function(event){

          if (event.keyCode === 37) {

             inputStates.left = true;

          } else if (event.keyCode === 38) {

             inputStates.up = true;

          } else if (event.keyCode === 39) {

             inputStates.right = true;

          } else if (event.keyCode === 40) {

             inputStates.down = true;

          }  else if (event.keyCode === 32) {

             inputStates.space = true;

          }

      }, false);

​

      //if the key will be released, change the states object 

      window.addEventListener('keyup', function(event){

          if (event.keyCode === 37) {

             inputStates.left = false;

          } else if (event.keyCode === 38) {

             inputStates.up = false;

          } else if (event.keyCode === 39) {

             inputStates.right = false;

          } else if (event.keyCode === 40) {

             inputStates.down = false;

          } else if (event.keyCode === 32) {

             inputStates.space = false;

          }

      }, false);

      // Mouse event listeners

      canvas.addEventListener('mousemove', function (evt) {

          inputStates.mousePos = getMousePos(evt);

      }, false);

​

      canvas.addEventListener('mousedown', function (evt) {

            inputStates.mousedown = true;

            inputStates.mouseButton = evt.button;

      }, false);

​

      canvas.addEventListener('mouseup', function (evt) {

          inputStates.mousedown = false;

      }, false);      

​

​

        // start the animation

        requestAnimationFrame(mainLoop);

    };

​

    //our GameFramework returns a public API visible from outside its scope

    return {

        start: start

    };

};

​

​