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Moving image on canvas on the X axis only

The Problem
I am finding it rather difficult to get my head around this, I am attempting to move an image using the mouse along the X axis only. I am finding it hard to even move the image at all and the many tutorials I have looked at arnt really helping me. Here is what I am trying to say:
As you can see by my beautiful image above I only want to image to move left and right at the bottom of the page.
The Code and the Question
Here is my first attempt, when I try this all the images loaded on the canvas no longer appear making it very hard for me to understand why it isnt working.
<script type="text/javascript">
//Referencing the canvas
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var width = canvas.getAttribute('width');
var height = canvas.getAttribute('height');
//Images
var bggameImage = new Image();
var playerImage = new Image();
var enemyImage = new Image();
var projectileImage = new Image();
var livesImage = new Image();
//Canvas dimensions
var width = 480;
var height = 320;
//Loading in the backgroundImage
bggameImage.src = "Images/bggameImage.png";
bggameImage.onload = function(){
context.drawImage(bggameImage, 0, 0);
}
//Loading in the playerImage
playerImage.src = "Images/playerImage.png";
playerImage.onload = function(){
context.drawImage(playerImage, 165, 240);
}
//Loading in the projectileImage
projectileImage.src = "Images/projectileImage.png";
projectileImage.onload = function(){
context.drawImage(projectileImage, 65, 240);
}
var playerImage = {
x:176,
y:74,
}
function init() {
playerImage.src = "Images/playerImage.png";
//Moving player
myCanvas.addEventListener("mousemove", function (e) {
var bounding_box = myCanvas.getBoundingClientRect();
playerImage = (e.clientX - bounding_box.left) * (myCanvas.width / bounding_box.width) - playerImage.width / 2;
playerImage = (e.clientY - bounding_box.top) * (myCanvas.height / bounding_box.height) - playerImage.height / 2;
}
)
</script>
The whole "function init()" part is what I have just tried but I thought I would include this anyway, I understand that I am loading in the playerImage twice.

You're using the same variable name twice (playerImage), so your image is being overwritten. You're using it for the image and also to store the position. Change the playerImage that's storing x and y to be playerPosition or something like that. Update that variable on your mouse event and then render the image according to that variable's values.
Ultimately, you're going to have to look at a game loop using setTimeout or requestAnimationFrame. So, this will become crucial at that stage. And yes, you shouldn't be loading the player image twice either. Do all of that at the start and only start your game when all your assets have successfully loaded.
For instance...
var playerImage;
var alienImage;
var bulletImage;
var assetCount = 0;
function loadAssets() {
playerImage = new Image();
playerImage.onload = checkAssetsLoaded;
playerImage.src = "assets/images/Brush01.png";
alienImage = new Image();
alienImage.onload = checkAssetsLoaded;
alienImage.src = "assets/images/Brush02.png";
bulletImage = new Image();
bulletImage.onload = checkAssetsLoaded;
bulletImage.src = "assets/images/Brush03.png";
}
function checkAssetsLoaded(event) {
assetCount++;
console.log("An asset has loaded!: " + assetCount);
if (assetCount == 3) {
startGame();
}
}
function startGame() {
// Start your game initialization logic here.
console.log("Game starting!");
}

Creating a scratch card in EaselJS

I've been trying to develop a scratch card in EaselJS.
So far, I've managed to get a Shape instance above a Bitmap one and enabled erasing it with click and drag events, so the image below becomes visible.
I've used the updateCache() with the compositeOperation approach and it was easy enough, but here is my issue:
How can I find out how much the user has already erased from the Shape instance, so I can setup a callback function when, say, 90% of the image below is visible?
Here is a functioning example of what I'm pursuing: http://codecanyon.net/item/html5-scratch-card/full_screen_preview/8721110?ref=jqueryrain&ref=jqueryrain&clickthrough_id=471288428&redirect_back=true
This is my code so far:
function Lottery(stageId) {
this.Stage_constructor(stageId);
var self = this;
var isDrawing = false;
var x, y;
this.autoClear = true;
this.enableMouseOver();
self.on("stagemousedown", startDrawing);
self.on("stagemouseup", stopDrawing);
self.on("stagemousemove", draw);
var rectWidth = self.canvas.width;
var rectHeight = self.canvas.height;
// Image
var background = new createjs.Bitmap("http://www.taxjusticeblog.org/lottery.jpg");
self.addChild(background);
// Layer above image
var overlay = new createjs.Shape();
overlay.graphics
.f("#55BB55")
.r(0, 0, rectWidth, rectHeight);
self.addChild(overlay);
overlay.cache(0, 0, self.canvas.width, self.canvas.height);
// Cursor
self.brush = new createjs.Shape();
self.brush.graphics
.f("#DD1111")
.dc(0, 0, 5);
self.brush.cache(-10, -10, 25, 25);
self.cursor = "none";
self.addChild(self.brush);
function startDrawing(evt) {
x = evt.stageX-0.001;
y = evt.stageY-0.001;
isDrawing = true;
draw(evt);
};
function stopDrawing() {
isDrawing = false;
};
function draw(evt) {
self.brush.x = self.mouseX;
self.brush.y = self.mouseY;
if (!isDrawing) {
self.update();
return;
}
overlay.graphics.clear();
// Eraser line
overlay.graphics
.ss(15, 1)
.s("rgba(30,30,30,1)")
.mt(x, y)
.lt(evt.stageX, evt.stageY);
overlay.updateCache("destination-out");
x = evt.stageX;
y = evt.stageY;
self.update();
$rootScope.$broadcast("LotteryChangeEvent");
};
}
Any ideas?

That's a tricky one, regardless of the language. The naive solution would simply be to track the length of the paths the user "draws" within the active area, and then reveal when they scratch long enough. That's obviously not very accurate, but is fairly simple and might be good enough.
The more accurate approach would be to get the pixel data of the cacheCanvas, then check the alpha value of each pixel to get an idea of how many pixels are transparent (have low alpha). You could optimize this significantly by only checking every N pixel (ex. every 5th pixel in every 5th row would run 25X faster).

How do I capture the onclick event called in HTML?

So, I have an <img> tag that has an onclick attribute. The onclick calls a function called analyze(this), with this being the image.
The analyze function does some things to the image that aren't entirely relevant, except for the fact that it draws it onto the <canvas> element (using the drawImage function).
But now, I want to also pick the color I just clicked on in the image. I am currently using the method answered here (the answer with 70+ votes, not the chosen one): How do I get the coordinates of a mouse click on a canvas element?
But, I think I might be doing this wrong. I have the image drawn and my functions called (and those all work), but the color picking part isn't being called. I think that this is because I didn't actually capture the event. This is generally how my code looks:
<img onclick="javascript:analyze(this);" />
function analyze(img_elem) {
// This is getting the canvas from the page and the image in it
var canvaselement = document.getElementById('canvas').getContext('2d'),
img = new Image();
img.onload = function () {
canvaselement.drawImage(img, 0, 0, 250, 250);
...
canvaselement.onClick = function () {
var coords = canvaselement.relMouseCoords(event);
pick(img, canvaselement, coords); // pass in coordinates
}
}
img.src = img_elem.src;
}
function relMouseCoords(event) {
var totalOffsetX = 0;
var totalOffsetY = 0;
var canvasX = 0;
var canvasY = 0;
var currentElement = this;
do {
totalOffsetX += currentElement.offsetLeft - currentElement.scrollLeft;
totalOffsetY += currentElement.offsetTop - currentElement.scrollTop;
}
while (currentElement = currentElement.offsetParent)
canvasX = event.pageX - totalOffsetX;
canvasY = event.pageY - totalOffsetY;
return {
x: canvasX,
y: canvasY
}
}
function pick(img, canvaselement, coords) {
var pickedColor = "";
canvaselement.drawImage(img, 0, 0, 250, 250);
xx = coords.x;
yy = coords.y;
var imgData = canvas.getImageData(xx, yy, 1, 1).data;
pickedColor = rgbToHex(imgData);
//alert(pickedColor);
return pickedColor;
}
So, the code never gets to the pick function. I have a feeling that it's because I didn't actually capture the onclick event. I'm also not even sure if this is the right way to get the coordinates on the canvas, I'm just sort of hoping that I even get to that part of the debugging process at this point.
Thanks for your help!

The problem is probably that you're assigning canvaselement to the results of getContext('2d') and not to the element itself, which you will need for the click event binding. Create two variables, one for the DOM element itself and one for the context, something like:
var canvaselement = document.getElementById('canvas'),
canvaselementctx = canvaselement.getContext('2d');
...
canvaselement.onClick = function() {
var coords = canvaselementctx.relMouseCoords(event);
...
}

You have a couple of errors in the code but the reason the code you got from the linked post is that you forgot to include the prototype definition it uses:
HTMLCanvasElement.prototype.relMouseCoords = relMouseCoords;
Now you can call relMouseCoords on the canvas element:
/// event name in lower case
canvaselement.onclick = function () {
var coords = canvaselement.relMouseCoords(event);
//...
However, you will still get problems as you don't use a canvas context for the drawing calls.
function analyze(img_elem) {
// This is getting the canvas from the page and the image in it
var canvaselement = document.getElementById('canvas').getContext('2d'),
/// get context like this
ctx = canvaselement.getContext('2d'),
img = new Image();
img.onload = function () {
/// use context to draw
ctx.drawImage(img, 0, 0, 250, 250);
//...

JavaScript iteration

I want to use JavaScript to draw a series of images onto an HTML5 canvas. I have the following while loop, which I had hoped would draw all of the images to the canvas, however, it is currently only drawing the first one:
function drawLevelOneElements(){
/*First, clear the canvas */
context.clearRect(0, 0, myGameCanvas.width, myGameCanvas.height);
/*This line clears all of the elements that were previously drawn on the canvas. */
/*Then redraw the game elements */
drawGameElements();
/*Draw the elements needed for level 1 (26/04/2012) */
var fileName = 1;
var imagePositionX = 20;
var imagePositionY = 30;
while(fileName < 11){
/*Create an array of images here, move to next element of array on each iteration */
var numbers = new Array();
numbers[0] = "1.png"
numbers[1] = "2.png"
numbers[3] = "3.png"
numbers[4] = "4.png"
numbers[5] = "5.png"
image.src = fileName+".png";
image.src = numbers[0];
image.onload = function(){
context.drawImage(image, imagePositionX, imagePositionY, 50, 50);
}
fileName = fileName+1;
imageY = imageY+20;
console.dir(fileName); /* displays in the console- helpful for debugging */
}
To talk through what I had hoped this function would do:
Load each of the images into a different element of the array (so 1.png would be in numbers[0], 2.png in numbers[1], etc. )
It would then take the global variable 'image', and assign its source to the contents of numbers[0]
Then draw that image at the specified position on the canvas.
Then increment the value of the variable fileName by 1, giving it a value of '2'
Next it would increment the value of the Y co-ordinate where it will draw the image on the canvas by 20- moving the position of the image to be drawn down by 20 pixels
After that it would go back to the start of the loop and draw the next image (2.png) on the canvas in a position that is 20 pixels below the position of the first image that was drawn.
It should continue doing this while the value of the variable 'fileName' is less than 11, i.e. it should draw 10 images each new one below the last one that was drawn.
However, for some reason, my function only draws the first image. Could someone point out what I'm doing wrong, and how I could correct this?
Thanks very much.

Edited and commented some points of your code.
The most effective change was at imageY = imageY+20; that was edited to use imagePositionY variable.
function drawLevelOneElements() {
/*First, clear the canvas */
context.clearRect(0, 0, myGameCanvas.width, myGameCanvas.height);
/*This line clears all of the elements that were previously drawn on the canvas. */
/*Then redraw the game elements */
drawGameElements();
/*Draw the elements needed for level 1 (26/04/2012) */
var fileName = 1;
var imagePositionX = 20;
var imagePositionY = 30;
while(fileName < 11){
/*Create an array of images here, move to next element of array on each iteration */
var numbers = new Array();
/* what is not used is not necessary :)
numbers[0] = "1.png"
numbers[1] = "2.png"
numbers[3] = "3.png"
numbers[4] = "4.png"
numbers[5] = "5.png"*/
image.src = fileName+".png";
// image.src = numbers[0];
image.onload = function(){
context.drawImage(image, imagePositionX, imagePositionY, 50, 50);
}
fileName = fileName+1;
imagePositionY = imagePositionY+20; //before: imageY = imageY+20;
console.dir(fileName); /* displays in the console- helpful for debugging */
}

If you take the drawImg stuff and shove it in its own function you can clean this up a bit :) Now we've yanked the async stuff out of the loop, so the image variable doesn't get over-written each time you loop. You're also using a for loop now, which to me is clearer to understand.
function drawLevelOneElements() {
// your stuff
for (var i = 0; i > 5; i++) {
drawImg(ctx, i, x, y);
// update x or y and whatever else
}
}
// put all your image drawing stuff here
function drawImg(ctx, i, x, y) {
var img = new Image();
img.src = i + ".png";
img.onload = function(){
ctx.drawImage(img, x, y, 50, 50);
}
}

How i can get hit test with image on canvas?

I create image in this way:
var orc = new Image();
orc.src = "./orc.png";
I use image in objects like this:
function Character(hp, image){
this.hp = hp;
this.image = image;
};
I call it in several times, like:
unit245 = new Character(100, orc);
And I draw it in this way, for example:
ctx.drawImage(unit245.image, 15, 55, 100, 100);
How I can get mouse click or move above my unit245 on canvas?
I need something like this http://easeljs.com/examples/dragAndDrop.html but without any frameworks (except jquery)

There is no built in way. I've written a few tutorials on making movable and selectable shapes on a Canvas to help people get started with this sort of thing though.
In short you need to remember what you have drawn and where, and then check each mouse click to see if you have clicked on something.

HitTesting can be done by checking what is present at the current location over the canvas, which can be called upon mouse click or move event over the canvas (which is the basis of hit testing). This can be done by knowing what has been placed where, like the bounds of an image can be saved, and when user clicks somewhere or moved the mouse over the canvas, you can check whether it is inside the image bounds or outside it. Array or List can be used for this.
Here is how this can be done

You cannot. The canvas has no semblance of what your unit245 or Character object is. You will have to actually manually check the coordinates and see if they fall within the bounds that you have for the character.
For example (assuming your Canvas is a var named canvas):
canvas.onclick = function(e) {
if (e.x >= unit245.x && e.x <= unit245.x + unit245.width && e.y >= unit245.y && e.y <= unit245.y + unit245.height) {
alert("You clicked unit245!");
}
}
In your case:
unit245.x = 15
unit245.y = 55
unit245.width = 100
unit245.height = 100

function Item(img, x, y){
this.image = img;
this.x = x;
this.y = y;
this.canv = document.createElement("canvas");
this.canv.width = this.image.width;
this.canv.height = this.image.height;
this.ctx = this.canv.getContext('2d');
this.ctx.drawImage(this.image, 0, 0, CELL_SIZE, CELL_SIZE);
this.hit = function (mx, my) {
var clr;
clr = this.ctx.getImageData(mx - this.x, my - this.y, 1, 1).data;
if (clr[3] > 250) {
//On object
this.image = gold_glow;
} else {
//Leave object
this.image = gold;
}
};
}