Develop Reference

How to use .onclick event for multiple times?

For example, I have a rectangle on my html page, and want to rotate it for 90deg by clicking on it:
rectangle.onclick = () => {
rectangle.style.transform = "rotate(90deg)";
When I click once - it rotates,but when i wanna rotate it for the second time - it does not work. Is there any way to to use .onclick event for two or more times?

CSS is not stateful; that is, when you set "rotate(90)" it doesn't rotate the item 90 degrees further, it rotates it to exactly 90 degrees from 0. So, if you want to rotate it, you need to set the correct angle: 90, 180, 270, &c. You can use a simple state variable to keep track of your angle, like this:
let rotation = 0 // rotation angle variable
rectangle.onclick = () => {
if (rotation >= 360) {
rotation = 0
} else {
rotation += 90;
}
rectangle.style.transform = `rotate(${rotation}deg)`;
}

When you set pentangle.style.transform, you're setting a style. That transform is from the baseline, unrotated shape. Your onclick event is likely getting fired multiple times, but each time, it does the same thing: cause the pentangle to be rotated from its default orientation.
You'll need something more like this, which advances the rotation amount based on the current rotation.
pentangle.onclick = () => {
if(pentangle.style.transform == "rotate(90deg)")
pentangle.style.transform = "rotate(180deg)";
else if(pentangle.style.transform == "rotate(180deg)")
pentangle.style.transform = "rotate(270deg)";
else if(pentangle.style.transform == "rotate(270deg)")
pentangle.style.transform = "";
else
pentangle.style.transform = "rotate(90deg)";

FabricJS - Better solution to centering object on cursor when selected?

I would like selectable objects to snap their center to my mouse cursor on click. The only modification allowed to the user in this case is moving the object, no scaling, rotating, etc. Simply updating the position of the object on mousedown or selected will update its position only until the moving event is fired, where the object will snap to its original position and then begin following the mouse.
rect.on('moving', moveHandler);
function moveHandler(evt) {
var mousePnt = $canvas.getPointer(evt.e);
rect.set({
left:mousePnt.x - rect.width*0.5 , top:mousePnt.y - rect.height*0.5});
this.setCoords();
}
This is what I've come up with to center a selectable rectangle on the cursor, but I'm certain it's firing two movement events. Is there a way to override that original positioning. Or should I instead write my own mousedown, mouseup, and moving listeners to mimic the default dragging behavior?

You solution is fine if no rotating or scaling is involved.
You are not executing anything more than necessary if not the .setCoords that during a movement is optional since it will be called on mouseUp when the translation is finished.
If you want to take the mouseDown approach, changing the position once for all, you can use this logic:
var canvas = new fabric.Canvas('c');
canvas.add(new fabric.Rect({width: 50, height: 50}));
canvas.on('mouse:down', function(opt) {
if (this._currentTransform && opt.target) {
var target = opt.target;
target.top = this._currentTransform.ey - target.height/2;
target.left = this._currentTransform.ex - target.width/2;
this._currentTransform.left = target.left;
this._currentTransform.offsetX = this._currentTransform.ex - target.left;
this._currentTransform.offsetY = this._currentTransform.ey - target.top;
this._currentTransform.top = target.top;
this._currentTransform.original.left = target.left;
this._currentTransform.original.top = target.top;
this.renderAll();
}
})
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.18/fabric.min.js"></script>
<canvas id="c" ></canvas>
You have to modify all the transform information that fabric noted down on the mouseDown event before the your mousedown handler is executed.

CreateJs - Controlling timeline playhead with click & drag

First time posting here, hope I'm doing this right :) I am trying to create a 360 spin in Adobe Animate with createJS, using a sequence of images embedded in a MovieClip. I have managed to get control of the timeline playhead using the code below:-
var start_x;
var startFrame;
var changeDistance;
var travelDistance;
this.threeSixty.addEventListener("mousedown", onMouseDown.bind(this));
this.threeSixty.addEventListener("pressup", onMouseUp.bind(this));
function onMouseDown(e) {
start_x = e.stageX;
startFrame = this.threeSixty.timeline.position;
this.threeSixty.addEventListener("pressmove", onMouseMove.bind(this));
}
function onMouseUp(e) {
this.threeSixty.removeEventListener("pressmove", onMouseMove.bind(this));
}
function onMouseMove(e) {
var changeDistance = e.stageX-start_x;
var travelDistance = startFrame+changeDistance;
if (travelDistance > this.threeSixty.timeline.duration){
this.threeSixty.gotoAndStop(travelDistance % this.threeSixty.timeline.duration);
}else if (travelDistance < 0){
this.threeSixty.gotoAndStop (this.threeSixty.timeline.duration + (travelDistance % threeSixty.timeline.duration));
} else {
this.threeSixty.gotoAndStop(travelDistance);
}
}
The problem is, when you click and drag the image along the X axis, the image sequence only moves forward/backwards by a single frame, as opposed to continuing the image sequence until the either mouse has stopped moving, or the mouse click is released. Any ideas where I might be going wrong here?
Thanks

Trying to drag ship on canvas from left to right in Space Invaders clone

I have a "ship" that I have drawn on my canvas and I want to be able to drag it left and right on the bottom of the canvas when it is clicked. I have done some research but I'm having no luck.
I'm assuming I use onMouseDown to do this so I have this when the page loads...
canGame.onMouseDown = canCanvas.onMouseDown(e);
and here is the code that creates my ship
gShip = spriteNew("MediumSpringGreen", 230, 950, 150, 20);
From there I am not really sure what to do. I have a gameUpdate function which moves the invaders down the screen. A gameInit function that will draw the invaders and ship on the screen. Also I have a gameDraw function which draws everything on the screen. I have a few others which are not really important for my issue.
Here is the jsfiddle with the full source code. For some reason though it will run on my browser when I run the HTM file but not in jsfiddle.
http://jsfiddle.net/f66bk/2/

Like I said in comment, the best way of doing this kind of behaviour is by using the events mouseup, mousedown and mousemove.
I defined a var named isMouseDown to know that the ship is dragged that I set to true on mousedown and false on mouseup:
canGame.onMouseDown = function() { isMouseDown = true }
canGame.onMouseUp = function() { isMouseDown = false }
You will also need the event onmousemove to get your mouse position to redraw your ship properly:
canGame.onMouseUp = function(event) { moveShip(event, this) }
In the function moveShip, you can get your mouse position and set the position of your ship properly:
function moveShip(evt, obj) {
if(!isMouseDown)
return;
var target = evt.target || evt.srcElement,
rect = target.getBoundingClientRect(),
offsetX = evt.clientX - rect.left;
gShip.Rect.X = offsetX - gShip.Rect.Width/2;
}
Here is your jsfiddle :)

rotate a globe with the mouse

I can determine where on a globe the user has clicked.
When the user first clicks the mouse button down, I can store where they have clicked; lets call it the pin.
Then, as they drag the mouse around, I want to put the pin under the mouse cursor.
Here is some code that seems to roughly keep the pin under the mouse pointer, but doesn't correctly maintain the globe; it flickers and spins randomly. Sometimes it flips the axis entirely so the globe is momentarily back-to-front.
function evtPos(evt) {
if(!scene.ortho) return null;
var x = lerp(scene.ortho[0],scene.ortho[1],evt.clientX/canvas.width),
y = lerp(scene.ortho[3],scene.ortho[2],evt.clientY/canvas.height), // flipped
sqrd = x*x+y*y;
return (sqrd > 1)?
null:
mat4_vec3_multiply(mat4_inverse(scene.mvMatrix),[x,y,Math.sqrt(1-sqrd)]);
}
function onMouseDown(evt) {
pin = evtPos(evt);
}
function onMouseMove(evt,keys,isMouseDown) {
if(!isMouseDown) return;
var pt = evtPos(evt);
if(pin == null) pin = pt;
if(pt == null) return;
var d = vec3_sub(pt,pin),
rotx = Math.atan2(d[1],d[2]),
roty = (d[2] >= 0)?
-Math.atan2(d[0] * Math.cos(rotx),d[2]):
Math.atan2(d[0] * Math.cos(rotx),-d[2]),
rotz = Math.atan2(Math.cos(rotx),Math.sin(rotx)*Math.sin(roty));
scene.mvMatrix = mat4_multiply(scene.mvMatrix,mat4_rotation(rotx,[1,0,0]));
scene.mvMatrix = mat4_multiply(scene.mvMatrix,mat4_rotation(roty,[0,1,0]));
scene.mvMatrix = mat4_multiply(scene.mvMatrix,mat4_rotation(rotz,[0,0,1]));
}
function onMouseUp(evt) {
pin = null;
}
Also, over time, an error seems to build up and the pin drifts further and further from the mouse pointer. I presume I should somehow compute the mvMatrix completely rather than by lots of samll increments each event?
I want the user to be able to drag the globe around to navigate naturally. All code to spin globes that I've found uses fixed speeds e.g. arrow keys, rather than 'pinning' the globe under a mouse pointer. Unity has a function Quaternion.FromToRotation(fromPos,toPos) which seems very promising but the source is not available.

One of the approaches for doing this is the arcBall algorithm. There are even JavaScript implementations available so you don't need to roll your own.