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Find a point old position after zoom using java script

I am working on this "simple" problem for hours with no success, although I tried many ways to solve it using all kind of solutions suggested in SO.
My problem is as follows:
I have a point on a canvas, which when I click on it my app does something, after identifying the point by comparing the mouse click coordinates to the stored position of the point.
After zooming into the point, using the mouse wheel, I click on the point again but the mouse coordinates no longer fits the stored position of the point.
I need to either transform the mouse coordinates to it's coordinates before the zoom, so I will be able to compare to the stored position, or to transform the stored position to the new canvas so it can be compare to the coordinates of the mouse. Any of the solution is fine by me.
I know the following data:
The "scale" value,
The size of the canvas (top, left, width, height),
The new origin of the canvas (top, left)
I would like a solution using java script.

Finally figured it out and it is quite simple, once I understood the concept.
Save the new canvas origin after doing the zoom (in JS it is calling ctx.translate() and ctx.scale(), where ctx is the canvas context.
When need to calculate the mouse position in the old coordinate system, one has to add back the moved origin of the canvas, and multiply by the scale factor.
seat.x = (-new_org.x + pos.x) / scale;
seat.y = (-new_org.y + pos.y) / scale;
where pos is the calculated mouse pointer
pos.x = event.clientX - .getBoundingClientRect().left;
pos.y = event.clientY - .getBoundingClientRect().top;

Use of absolutePan() to move background image and elements around on canvas with touch event

I am using next code to force content of canvas to follow finger touch movement on screen (drag and drop).
document.addEventListener('touchmove', function(e){
if(e.targetTouches.length ==1) {
var canavasMovex=e.targetTouches[0].pageX-canvasLeftofset-canvas.width/2;
var canavasMovey=e.targetTouches[0].pageY-canvasTopofset-canvas.height/2;
document.getElementById("a").innerHTML= canavasMovex;
document.getElementById("b").innerHTML= canavasMovey;
var delta = new fabric.Point(-canavasMovex,-canavasMovey);
canvas.absolutePan(delta);
canvas.renderAll();
}
}, false);
Note: "-canavasMovex,-canavasMovey" values have the negative sign (I had to use it because otherwise the canvas was moving opposite to finger moment(I think you can ignore this fact and that it has noting to do with offset, which I am trying to solve asking for help here))
I have displacement of position proportional to the distance of touch point from the centre of canvas. If I start the movement pressing from the centre of screen, then displacement is not so notable. But if I start from top corner (for example) I get centre of canvas there in that touch point. From attached drawing I was trying with taking of consideration of "d" parameter (distance of touching point to the centre of canvas), to find right value for the equation for the canvas.absolutePan() function, but no success. Can you help me with this case,pleas? I was trying to use some solutions from browsing the internet to find the way to move canvas content. But then I had lost some of functions of my app because "new" libraries were not interacting correctly with my existing fabric.min.js library. Image info(external rectangle-web page,internal rectangle-canvas): a-canvas offset,b-distance to centre of canvas,c- touch point,d-distance from touch point to centre of canvas. So on the end I am trying to get to accomplish this task in this way.
Malfunction:
Bigger than distance "d" is on starting of dragging , bigger is then the offset. (actuary if I start dragging from canvas corner, canvas content transfers its centre there)

The solution is to get the finger position, calculate the difference to previous position, add difference to the previous position and then finally do the panning.
var canvasMovexoold = 0;
var canvasMoveyoold = 0;
document.addEventListener('touchstart', function(e){
canvasMovexoold = canvasLeftofset+canvas.width/2-e.targetTouches[0].pageX;
canvasMoveyoold =canvasTopofset+canvas.height/2- e.targetTouches[0].pageY;
}, false);
document.addEventListener('touchmove', function(e){
if(e.targetTouches.length ==1) {
var canvasMovexo += canvasLeftofset+canvas.width/2-e.targetTouches[0].pageX-canvasMovexoold ;
var canvasMoveyo +=canvasTopofset+canvas.height/2- e.targetTouches[0].pageY-canvasMoveyoold ;
var delta = new fabric.Point(canvasMovexo,canvasMoveyo);
canvas.absolutePan(delta);
canvasMovexoold = canvasLeftofset+canvas.width/2-e.targetTouches[0].pageX;
canvasMoveyoold =canvasTopofset+canvas.height/2- e.targetTouches[0].pageY;
}
}, false);

Rotate div to face mouse cursor running slowly using vanilla javascript and velocity.js

I am trying to create div that 3D rotates on the X and Y axis so that it always faces the mouse cursor.
I am using vanilla Javascript and Velocity.js for the animation library.
Here is my Javascript code so far, please see the Codepen link for the html and css too:
var el = document.querySelector("#circle");// get mouse position on x y
onmousemove = function(event) {
var x = event.clientX
var y = event.clientY
var HEIGHT = document.body.clientHeight;
var WIDTH = document.body.clientWidth;
console.log("x position: "+ x +", " + "y position: " + y);
var calcX= Math.floor(x/10)
var calcY= Math.floor(y/10)
Velocity(el, {rotateX:calcX})
Velocity(el, {rotateY:calcY})
// rotate element towards x and y co-ordinates
};
http://codepen.io/anon/pen/bpzjar
I know that the math calculation isn't correct, if someone knows what the correct code for that, that would be awesome!
But I'm mainly trying to look at why the code is so slow and it seems to calculate and go to through each degree rather than going straight to what the final calculation would be so that its fast and responsive.
If someone could help me figure it out that would be great.
thanks!

As a calculation approach you can map your mouse position to degree values:
var calcY = Math.round(map_range(x, 0, WIDTH, -60, 60));
var calcX = Math.round(map_range(y, 0, HEIGHT, 60, -60));
function map_range(value, low1, high1, low2, high2) {
return low2 + (high2 - low2) * (value - low1) / (high1 - low1);
}
Javascript has not native Math.map function but the simple helper included above will do it (credit to this SO answer)
This will rotate between from -60 to 60 degrees on both axis.
See the codePen example for this.
As others have already mentioned; Velocity.js is more for transitions (over time animations) and you don't need it for just follow mouse interactions.
Nevertheless you can use as well the .hook function helper from Velocity.js -
which jumps directly to a value (this is what I've used in the codePen example).
Velocity.hook(el, "rotateX", calcX+"deg");
Velocity.hook(el, "rotateY", calcY+"deg");

By default, velocity.js has a duration of 400 milliseconds for transforms. Every time your mouse cursor changes position, rotateX will queue up a new ease to the new rotation.
Maybe this is closer to what you want:
Velocity(el, {rotateX:calcX, duration:10}, { queue: false })
Velocity(el, {rotateY:calcY, duration:10}, { queue: false })

You don't need velocity for what you want.
All you need is requestAnimationFrame (velocity uses it inside). Please read this post by Paul Irish, he explain how to use requestAnimationFrame better than me
And please see this working fiddle https://jsbin.com/vekuce.
Hope it help.

Parallax effect with zoom and rotating

I am currently experimenting with parallax effect that i am planning to implement to my HTML5-canvas game engine.
The effect itself is fairly easy to achieve, but when you add zooming and rotating, things get a little more complicated, at least for me. My goal is to achieve something like this:Youtube video.
As you can see, you can zoom in and out "to the center", and also rotate around it and get the parallax effect.
In my engine i want to have multiple canvases that are going to be my parallax layers, and i am going to translate them.
I came up with something like this:
var parallax = {
target: {
x: Mouse.x,
y: Mouse.y
},
offset: {
x: -ctx.width / 2,
y: -ctx.height / 2
},
factor: {
x: 1,
y: 1
}
}
var angle = 0;
var zoomX = 1;
var zoomY = 1;
var loop = function(){
ctx.canvas.width = ctx.canvas.width; //Clear the canvas.
ctx.translate(parallax.target.x * parallax.factor.x, parallax.target.y * parallax.factor.y);
ctx.rotate(angle);
ctx.scale(zoomX, zoomY);
ctx.translate((-parallax.target.x - parallax.offset.x) * parallax.factor.x, (-parallax.target.y - parallax.offset.y) * parallax.factor.y);
Draw(); //Function that draws all the objects on the screen.
}
This is a very small and simplified part of my script, but i hope that's enough to get what i am doing. The object "parallax" contains the target position, the offset(the distance from the target), and the factor that is determining how fast the canvas is moving away relatively to the target. ctx is the canvas that is moving in the opposite direction of the target.(In this example i am using only one layer.) I am using the mouse as the "target", but i could also use the player, or some other object with x and y property. The target is also the point around which i rotate and scale the canvas.
This method works completely fine as long as the factor is equal to 1. If it is something else, the whole thing suddenly stops working correctly, and when i try to zoom, it zooms to the top-left corner, not the target. I also noticed that if i zoom out too much, the canvas is not moving in the opposite way of the target, but in the same direction.
So my question is: What is the correct way of implementing parallax with zooming and rotating?
P.S. It is important to me that i am using canvases as the layers.

To prepare for the next animation frame, you must undo any previous transforms in the reverse order they were executed:
context.translate(x,y);
context.scale(sx,sy);
context.rotate(r);
// draw stuff
context.rotate(-r);
context.scale(-sx,-sy);
context.translate(-x,-y);
Alternatively, you can use context.save / context.restore to undo the previous transforms.
Adjust your parallax values for the current frame,
Save the un-transformed context state using context.save(),
Do your transforms (translate, scale, rotate, etc),
Draw you objects as if they were in non-transformed space with [0,0] at your translate point,
Restore your context to it's untransformed state using context.restore()/
Either way will correctly give you a default-oriented canvas to use for your next animation frame.
The exact parallax effects you apply are up to your own design, but using these methods will make the canvas return to a normal default state for you to design with.

How to get the correct mouse position in relation to a div that has has a scale transform applied

I am using CSS transform scale to create a smooth zoom on a div. The problem is that I want to be able to get the correct mouse position in relation to div even when scaled up, but I can seem figure out the correct algorithm to get this data. I am retrieving the current scale factor from:
var transform = new WebKitCSSMatrix(window.getComputedStyle($("#zoom_div")[0]).webkitTransform);
scale = transform.a;
When I read the position of the div at various scale settings it seems to report the correct position, i.e. when I scale the div until is is larger the the screen the position left and top values are negative and appear to be correct, as does the returned scale value:
$("#zoom_div").position().left
$("#zoom_div").position().top
To get the current mouse position I am reading the x and y position from the click event and taking away the offset. This works correctly at a scale value of 1 (no scale) but not when the div is scaled up. Here is my basic code:
$("#zoom_div").on("click", function(e){
var org = e.originalEvent;
var pos = $("#zoom_div").position();
var offset = {
x:org.changedTouches[0].pageX - pos.left,
y:org.changedTouches[0].pageY - pos.top
}
var rel_x_pos = org.changedTouches[0].pageX - offset.x;
var rel_y_pos = org.changedTouches[0].pageY - offset.y;
var rel_pos = [rel_x_pos, rel_y_pos];
return rel_pos;
});
I have made several attempts at multiplying dividing adding and subtracting the scale factor to/from from the pageX / Y but without any luck. Can anyone help me figure out how to get the correct value.
(I have simplified my code from the original to hopefully make my question clearer, any errors you may find in the above code is due to that editing down. My original code with the exception for the mouse position issue).
To illustrate what I am talking about I have made a quick jsfiddle example that allows the dragging of a div using translate3d. When the scale is normal (1) the div is dragged at the point where it is clicked. When the div is scales up (2) it no longer drags correctly from the point clicked.
http://jsfiddle.net/6EsYG/12/

You need to set the webkit transform origin. Basically, when you scale up it will originate from the center. This means the offset will be wrong. 0,0 will start in the center of the square. However, if you set the origin to the top left corner, it will keep the correct coordinates when scaling it. This is how you set the origin:
#zoom_div{
-webkit-transform-origin: 0 0;
}
This combined with multiplying the offset by the scale worked for me:
offset = {
"x" : x * scale,
"y" : y * scale
}
View jsFiddle Demo

dont use event.pageX - pos.left, but event.offsetX (or for some browser: event.originalEvent.layerX
div.on('click',function(e) {
var x = (e.offsetX != null) ? e.offsetX : e.originalEvent.layerX;
var y = (e.offsetY != null) ? e.offsetY : e.originalEvent.layerY;
});
see my jsFiddle exemple: http://jsfiddle.net/Yukulele/LdLZg/

You may embed the scaled content within an iframe. Scale outside the iframe to enable scaled mouse events within the iframe as mouse events are document scope.