This code should check the mouse position, and if the mouse clicks show this X and Y positions in the console, but it is ignoring the click event and printing in the console the cordinates of the mouse without the click.
How do I fix this?
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
canvas.addEventListener('mousemove', function(evt) {
var mousePos = getMousePos(canvas, evt);
canvas.addEventListener("click", check(mousePos.x,mousePos.y));
}, false);
function check(x,y){
console.log(x);
}
In this case it would be better to avoid nested eventListeners.
Also you might store the cursor position as a canvas.mouse property:
var canvas = document.querySelector('canvas');
canvas.addEventListener('mousemove', getMousePos);
canvas.addEventListener("click", check);
function getMousePos(evt) {
var rect = canvas.getBoundingClientRect();
canvas.mouse = {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
function check() {
console.log(canvas.mouse.x);
}
canvas {
width: 200px;
height: 200px;
background: #ddd
}
<canvas></canvas>
but it is ignoring the click event and printing in console the cordinates of the mouse without the click. How do i fix this?
It's doing that because of the mousemove is firing whenever you move the mouse inside the canvas, and this line :
canvas.addEventListener("click", check(mousePos.x,mousePos.y));
Is calling the check() function that's why it's printing without a click.
as a side note when supplying a call back don't use () because that is invoking the function, and whatever it returns will become the callback, instead you supply the name of the function.
canvas.addEventListener("click", check);
Since you want it to print mouse position on click, You don't necessarily need mousemove, a simple click event is enough
DEMO
var canvas = document.querySelector('canvas');
canvas.addEventListener("click", function(e) {
console.log('X:' + e.clientX, 'Y:' + e.clientY);
});
canvas {
width: 200px;
height: 200px;
background: dodgerblue;
}
<canvas></canvas>
Related
I'm wanting to implement canvas as background for my website so users can use their cursors to paint on the webpage like this codepen: https://codepen.io/cocotx/pen/PoGRdxQ?editors=1010
(this is an example code from http://www.dgp.toronto.edu/~clwen/test/canvas-paint-tutorial/)
if(window.addEventListener) {
window.addEventListener('load', function () {
var canvas, context;
// Initialization sequence.
function init () {
// Find the canvas element.
canvas = document.getElementById('imageView');
if (!canvas) {
alert('Error: I cannot find the canvas element!');
return;
}
if (!canvas.getContext) {
alert('Error: no canvas.getContext!');
return;
}
// Get the 2D canvas context.
context = canvas.getContext('2d');
if (!context) {
alert('Error: failed to getContext!');
return;
}
// Attach the mousemove event handler.
canvas.addEventListener('mousemove', ev_mousemove, false);
}
// The mousemove event handler.
var started = false;
function ev_mousemove (ev) {
var x, y;
// Get the mouse position relative to the canvas element.
if (ev.layerX || ev.layerX == 0) { // Firefox
x = ev.layerX;
y = ev.layerY;
} else if (ev.offsetX || ev.offsetX == 0) { // Opera
x = ev.offsetX;
y = ev.offsetY;
}
// The event handler works like a drawing pencil which tracks the mouse
// movements. We start drawing a path made up of lines.
if (!started) {
context.beginPath();
context.moveTo(x, y);
started = true;
} else {
context.lineTo(x, y);
context.stroke();
}
}
init();
}, false); }
The problem is that the cursor stops painting when I scroll until I move my mouse again. Any idea on how to keep cursor painting even when I scroll?
Thanks in advance! Much appreciated!
You will have to store the last mouse event and fire a new fake one in the scroll event.
Luckily, the MouseEvent constructor accepts an mouseEventInit object on which we can set the clientX and clientY values of our new event, so we just need to store these values from the previous event and dispatch it in the scroll event.
Now, I couldn't help but rewrite almost everything from your code.
It had a lot of checks for old browsers (like very old ones which should never face the web again anyway), you may want to add it again if you wish.
It wasn't clearing the context, meaning that every time it drew a new line, it also did draw again the previous lines over themselves, leading in fatter lines, with a lot of noise at the beginning, and smoother lines at the end.
This could be fixed in many ways, the less intrusive one was to just clear the context at each frame.
To get the relative mouse position, it now uses the clientX and clientY properties of the event.
And the rest of the changes is commented in the snippet.
window.addEventListener('load', function () {
const canvas = document.getElementById('imageView');
context = canvas.getContext("2d");
let last_event; // we will store our mouseevents here
// we now listen to the mousemove event on the document,
// not only on the canvas
document.addEventListener('mousemove', ev_mousemove);
document.addEventListener('scroll', fireLastMouseEvent, { capture: true } );
// to get the initial position of the cursor
// even if the mouse never moves
// we listen to a single mouseenter event on the document's root element
// unfortunately this seems to not work in Chrome
document.documentElement.addEventListener( "mouseenter", ev_mousemove, { once: true } );
// called in scroll event
function fireLastMouseEvent() {
if( last_event ) {
// fire a new event on the document using the same clientX and clientY values
document.dispatchEvent( new MouseEvent( "mousemove", last_event ) );
}
}
// mousemove event handler.
function ev_mousemove (ev) {
const previous_evt = last_event || {};
const was_offscreen = previous_evt.offscreen;
// only for "true" mouse event
if( ev.isTrusted ) {
// store the clientX and clientY props in an object
const { clientX, clientY } = ev;
last_event = { clientX, clientY };
}
// get the relative x and y positions from the mouse event
const point = getRelativePointFromEvent( ev, canvas );
// check if we are out of the canvas viewPort
if( point.x < 0 || point.y < 0 || point.x > canvas.width || point.y > canvas.height ) {
// remember we were
last_event.offscreen = true;
// if we were already, don't draw
if( was_offscreen ) { return; }
}
// we come from out-of-screen to in-screen
else if( was_offscreen ) {
// move to the previous point recorded as out-of-screen
const previous_point = getRelativePointFromEvent( previous_evt, canvas );
context.moveTo( previous_point.x, previous_point.y );
}
// add the new point to the context's sub-path definition
context.lineTo( point.x, point.y );
// clear the previous drawings
context.clearRect( 0, 0, canvas.width, canvas.height );
// draw everything again
context.stroke();
}
function getRelativePointFromEvent( ev, elem ) {
// first find the bounding rect of the element
const bbox = elem.getBoundingClientRect();
// subtract the bounding rect from the client coords
const x = ev.clientX - bbox.left;
const y = ev.clientY - bbox.top;
return { x, y };
}
});
#container {
width: 400px;
height: 200px;
overflow: auto;
border: 1px solid;
}
#imageView { border: 1px solid #000; }
canvas {
margin: 100px;
}
<div id="container">
<canvas id="imageView" width="400" height="300"></canvas>
</div>
What I mean is that the user presses a mouse button at point xy on an HTML canvas and while the mouse button is pressed the rectangle can be resized according to the movement of the cursor with point xy fixed. Like how highlighting works.
This is what I've got so far but it doesn't seem to be working:
canvas.addEventListener('mousedown', function(e){
var rectx = e.clientX;
var recty = e.clientY;
canvas.onmousemove = function(e){
var df = e.clientX;
var fg = e.clientY;
};
context.rect(rectx, recty, df-rectx, fg-recty);
context.stroke();
}, false);
Assuming there are no transforms (scale, translate) on your canvas context.
Basic steps for having a resizable rectangle are as follows:
Create a mousedown listener that sets a flag indicating the use is holding down the mouse button, as well as sets the "anchor," or initial coordinates.
Create a mouseup listener that unsets the flag.
Create a mousemove listener that, if the flag indicates the mouse is down, redraws the canvas with the rectangle's size changed according to mouse coordinates.
An important note is that client coordinates in the event object are relative to the page, not to your canvas element. You will frequently need to convert clientX and clientY into canvas coordinates:
var getCanvasCoords = function (clientX, clientY) {
var rect = canvas.getBoundingClientRect();
return {
x: clientX - rect.left,
y: clientY - rect.top
};
};
The first two steps look something like this:
var anchorX;
var anchorY;
var mouseDown = false;
canvas.addEventListener('mousedown', function (event) {
var coords = getCanvasCoords(event.clientX, event.clientY);
anchorX = coords.x;
anchorY = coords.y;
mouseDown = true;
});
canvas.addEventListener('mouseup', function (event) {
mouseDown = false;
});
And the mousemove handler:
canvas.addEventListener('mousemove', function (event) {
var coords = getCanvasCoords(event.clientX, event.clientY);
var width = coords.x - anchorX;
var height = coords.y - anchorY;
// clear canvas for redrawing
context.clearRect(0, 0, canvas.width, canvas.height);
context.fillRect(anchorX, anchorY, width, height);
});
Don't Render from mouse events!
The given answer is correct but it is not the best way to do this.
The are two reasons. First the mousemove event can fire up to 600+ times a second but the display only refreshes 60 times a second. Rendering from the input event is many time just a waste of CPU time as the results will be overwritten by the next mouse event before it is ever had a chance to be displayed.
The second reason is that dedicating an event listener to a single task makes it hard to add more functionality. You end up adding more and more code to the mousemove event to handle all the types of input, most of which can be ignored because of the high update speed of the mouse.
Mouse listeners
Mouse event listeners do the minimum possible. They just record the mouse state and no more. Also all mouse events return the mouse position. You should not ignore the mouse position for events like mouse down and up
The following function creates a mouse object for a element. The mouse object has the x,y position relative to the to left of the element, and the current button states for 3 buttons it is left to right button1, button2, button3.
Also when the mouse leaves the element and then releases the mouse button the mouse for the element will not see the mouseup event and not know the mouse button is up. To prevent the mouse buttons from getting stuck you turn off the buttons when the mouse leaves the element.
The best mouse listener is to the whole page as it can track mouse events that happen even when the mouse is outside the window/tab (if the window/tab has focus), but that is a little to complex for this answer.
Function to create a mouse for an element
function createMouse(element){
var mouse = {
x : 0,
y : 0,
button1 : false,
button2 : false,
button3 : false,
over : false,
};
function mouseEvent(event){
var bounds = element.getBoundingClientRect();
mouse.x = event.pageX - bounds.left - scrollX;
mouse.y = event.pageY - bounds.top - scrollY;
if(event.type === "mousedown"){
mouse["button"+event.which] = true;
} else if(event.type === "mouseup"){
mouse["button"+event.which] = false;
} else if(event.type === "mouseover"){
mouse.over = true;
} else if(event.type === "mouseout"){
mouse.over = false;
mouse.button1 = false; // turn of buttons to prevent them locking
mouse.button2 = false;
mouse.button3 = false;
}
event.preventDefault(); // stops default mouse behaviour.
}
var events = "mousemove,mousedown,mouseup,mouseout,mouseover".split(',');
events.forEach(eventType => element.addEventListener(eventType,mouseEvent));
mouse.remove = function(){
events.forEach(eventType => element.removeEventListener(eventType, mouseEvent));
}
return mouse;
}
Using the mouse
It is now just a matter of creating a mouse for the element
var canMouse = createMouse(canvas);
And then in your main render loop do the dragging.
var drag = {
x : 0,
y : 0,
x1 : 0,
y1 : 0,
dragging : false,
top : 0,
left : 0,
width : 0,
height : 0,
}
function mainLoop(){
if(canMouse.button1){ // is button down
if(!drag.dragging){ // is dragging
drag.x = canMouse.x;
drag.y = canMouse.y;
drag.dragging = true;
}
drag.x1 = canMouse.x;
drag.y1 = canMouse.y;
drag.top = Math.min(drag.y, drag.y1);
drag.left = Math.min(drag.x, drag.x1);
drag.width = Math.abs(drag.x - drag.x1);
drag.height = Math.abs(drag.y - drag.y1);
}else{
if(drag.dragging){
drag.dragging = false;
}
}
}
Putting it all together
function createMouse(element){
var mouse = {
x : 0,
y : 0,
button1 : false,
button2 : false,
button3 : false,
over : false,
};
function mouseEvent(event){
var bounds = element.getBoundingClientRect();
// NOTE getting the border should not be done like this as
// it will not work in all cases.
var border = Number(element.style.border.split("px")[0])
mouse.x = event.pageX - bounds.left - scrollX - border;
mouse.y = event.pageY - bounds.top - scrollY - border;
if(event.type === "mousedown"){
mouse["button"+event.which] = true;
} else if(event.type === "mouseup"){
mouse["button"+event.which] = false;
} else if(event.type === "mouseover"){
mouse.over = true;
} else if(event.type === "mouseout"){
mouse.over = false;
mouse.button1 = false; // turn of buttons to prevent them locking
mouse.button2 = false;
mouse.button3 = false;
}
event.preventDefault(); // stops default mouse behaviour.
}
var events = "mousemove,mousedown,mouseup,mouseout,mouseover".split(',');
events.forEach(eventType => element.addEventListener(eventType,mouseEvent));
mouse.remove = function(){
events.forEach(eventType => element.removeEventListener(eventType, mouseEvent));
}
return mouse;
}
var drag = {
x : 0,
y : 0,
x1 : 0,
y1 : 0,
dragging : false,
top : 0,
left : 0,
width : 0,
height : 0,
}
var ctx = canvas.getContext("2d");
ctx.strokeStyle = "black";
ctx.lineWidth = 1;
var mouse = createMouse(canvas);
function update(){
ctx.clearRect(0,0,canvas.width,canvas.height);
if(mouse.button1){ // is button down
if(!drag.dragging){ // is dragging
drag.x = mouse.x;
drag.y = mouse.y;
drag.dragging = true;
}
drag.x1 = mouse.x;
drag.y1 = mouse.y;
drag.top = Math.min(drag.y, drag.y1);
drag.left = Math.min(drag.x, drag.x1);
drag.width = Math.abs(drag.x - drag.x1);
drag.height = Math.abs(drag.y - drag.y1);
}else{
if(drag.dragging){
drag.dragging = false;
}
}
if(drag.dragging){
ctx.strokeRect(drag.left, drag.top, drag.width, drag.height);
}
requestAnimationFrame(update);
}
requestAnimationFrame(update);
canvas {
border : 1px solid black;
}
Click drag to draw rectangle.<br>
<canvas id="canvas" width= "512" height = "256"></canvas>
I'm trying to build a canvas that i can drag using mouse movement. And I'm doing something wrong that i cannot understand cause seems to work at first and then there is like an incremental error that make the canvas move too fast.
Considering the following code,
window.onload = function() {
var canvas = document.getElementById("canvas");
var context = canvas.getContext('2d');
function draw() {
context.fillRect(25, 25, 100, 100);
}
function clear() {
context.clearRect(0, 0, canvas.width, canvas.height);
}
var drag = false;
var dragStart;
var dragEnd;
draw()
canvas.addEventListener('mousedown', function(event) {
dragStart = {
x: event.pageX - canvas.offsetLeft,
y: event.pageY - canvas.offsetTop
}
drag = true;
})
canvas.addEventListener('mousemove', function(event) {
if (drag) {
dragEnd = {
x: event.pageX - canvas.offsetLeft,
y: event.pageY - canvas.offsetTop
}
context.translate(dragEnd.x - dragStart.x, dragEnd.y - dragStart.y);
clear()
draw()
}
})
}
live example on Plunker https://plnkr.co/edit/j8QCxwDzXJZN2DKszKwm.
Can someone help me to understand what piece I'm missing?
The problem your code has is that each time you move the rectangle blablabla px relative to the dragStart position, the translate() method is not based on dragStart position, but your current position.
To fix this, you should add the following after calling the translate method:
dragStart = dragEnd;
So that your position is also based on current mouse position.
I'm working on a project based on a nice little sample canvas drawing app someone else on the project downloaded and modified. We need to allow the user to click a button elsewhere on the page (not part of the canvas), and have it run a function that came with the sample app. However, the function is inside of a closure. Since I can't call the function directly (right? the closure prevents this? I don't often work with closures), I thought I'd be able to accomplish this by triggering a mouse event at the location the user would click to accomplish the same thing. It's not working, and I don't know why not.
I posted a greatly simplified version at this fiddle. Simple HTML code:
<div id="canvasDiv"></div>
<div id="buttonDiv">
<button>why can't I send a click to the canvas?</button>
</div>
And the simplified version of the downloaded sample app, plus my attempt to use jQuery's .trigger method to trigger the event:
var WM = {};
WM.drawingApp = function(options) {
"use strict";
var canvas, context,
// Add mouse and touch event listeners to the canvas
createUserEvents = function() {
var getElementPos = function(element) {
// straight-forward stuff removed for brevity's sake
return pos;
};
var press = function(e) {
// Mouse down location
var sizeHotspotStartX, toolIndex,
mouseX = (e.changedTouches ? e.changedTouches[0].pageX : e.pageX),
mouseY = (e.changedTouches ? e.changedTouches[0].pageY : e.pageY);
var elementPos = getElementPos(document.getElementById(options.canvasElementId || 'canvasDiv'));
mouseX -= elementPos.x;
mouseY -= elementPos.y;
announce(mouseX, mouseY);
};
var announce = function(x,y) { alert('press at: ' + x + ', ' + y); }
// Add mouse event listeners to canvas element
canvas.addEventListener("mousedown", press, false);
},
// Creates a canvas element, etc
init = function() {
// Create the canvas
canvas = document.createElement('canvas');
canvas.setAttribute('width', 100);
canvas.setAttribute('height', 100);
canvas.setAttribute('id', 'canvas');
document.getElementById(options.canvasElementId || 'canvasDiv').appendChild(canvas);
context = canvas.getContext("2d"); // Grab the 2d canvas context
createUserEvents();
};
init();
return {};
};
jQuery(document).ready(function() {
jQuery('#buttonDiv').on('click', 'button', function() {
var down = jQuery.Event("mousedown", {
pageX: 50,
pageY: 50
});
jQuery('#canvasDiv canvas').trigger(down);
});
});
As you can see by running the fiddle, if you click inside the box, you get an alert announcing where you clicked. But if you click the button, you don't get an alert. While writing this question, it occurred to me that maybe jQuery's .trigger method isn't a sufficient way to send the click. Its documentation page specifically says that .trigger "does not perfectly replicate a naturally-occurring event". We're open to solutions that don't involve jQuery.
You can define a variable var press; outside of WM, inside of WM, remove var before press and set press = function() {}. You should then be able to call press(down) at click of button
var press;
press = function(e) {
console.log(e);
// Mouse down location
var sizeHotspotStartX, toolIndex,
mouseX = (e.changedTouches ? e.changedTouches[0].pageX : e.pageX),
mouseY = (e.changedTouches ? e.changedTouches[0].pageY : e.pageY);
var elementPos = getElementPos(
document.getElementById(options.canvasElementId
|| 'canvasDiv')
);
mouseX -= elementPos.x;
mouseY -= elementPos.y;
announce(mouseX, mouseY);
};
jQuery(document).ready(function() {
jQuery('#buttonDiv').on('click', 'button', function() {
var down = jQuery.Event("mousedown", {
pageX: 50,
pageY: 50
});
press(down); // call `press` at `button` click
//jQuery('#canvasDiv canvas').trigger(down);
});
});
// based on http://www.williammalone.com/projects/html5-canvas-javascript-drawing-app-with-bucket-tool/
var press;
var WM = {};
WM.drawingApp = function(options) {
"use strict";
var canvas, context,
// Add mouse and touch event listeners to the canvas
createUserEvents = function() {
var getElementPos = function(element) {
var parentOffset, pos;
if (!element) {
pos = {
x: 0,
y: 0
};
} else {
pos = {
x: element.offsetLeft,
y: element.offsetTop
};
if (element.offsetParent) {
parentOffset = getElementPos(element.offsetParent);
pos.x += parentOffset.x;
pos.y += parentOffset.y;
}
}
return pos;
};
press = function(e) {
console.log(e)
// Mouse down location
var sizeHotspotStartX, toolIndex,
mouseX = (e.changedTouches ? e.changedTouches[0].pageX : e.pageX),
mouseY = (e.changedTouches ? e.changedTouches[0].pageY : e.pageY);
var elementPos = getElementPos(document.getElementById(options.canvasElementId || 'canvasDiv'));
mouseX -= elementPos.x;
mouseY -= elementPos.y;
announce(mouseX, mouseY);
};
var announce = function(x,y) { alert('press at: ' + x + ', ' + y); }
// Add mouse event listeners to canvas element
canvas.addEventListener("mousedown", press, false);
},
// Creates a canvas element, loads images, adds events, and draws the canvas for the first time.
init = function() {
// Create the canvas (Neccessary for IE because it doesn't know what a canvas element is)
canvas = document.createElement('canvas');
canvas.setAttribute('width', 100);
canvas.setAttribute('height', 100);
canvas.setAttribute('id', 'canvas');
document.getElementById(options.canvasElementId || 'canvasDiv').appendChild(canvas);
context = canvas.getContext("2d"); // Grab the 2d canvas context
createUserEvents();
};
init();
return {};
};
jQuery(document).ready(function() {
jQuery('#buttonDiv').on('click', 'button', function() {
var down = jQuery.Event("mousedown", {
pageX: 50,
pageY: 50
});
press(down)
//jQuery('#canvasDiv canvas').trigger(down);
});
});
var drawingApp = WM.drawingApp({
canvasElementId: "canvasDiv"
});
#canvasDiv canvas {
border: solid black 1px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js">
</script>
<div id="canvasDiv"></div>
<div id="buttonDiv">
<button>why can't I send a click to the canvas?</button>
</div>
jsfiddle https://jsfiddle.net/gkvdha3h/5/
I have a bar drew in Canvas.
When user clicks anywhere in the bar I want to get the start position. Then, the user drags the mouse to any position and releases the mouse and I would get the last position.
I've been doing that for some time but I couldn't get the right events.
Here's my code.
<canvas id="demoCanvas" width="500" height="300"></canvas>
var stage = new createjs.Stage("demoCanvas");
var rect = new createjs.Shape();
rect.graphics.beginFill("#000").drawRect(0, 20, 200, 50);
rect.on('mousedown', function (mousedownEvent) {
var startX = mousedownEvent.rawX;
console.log('mousedown');
});
rect.on('mouseup', function(mouseupEvent) {
var stopX = mouseupEvent.rawX;
console.log('mouseup');
console.log(stopX);
});
stage.addChild(rect);
stage.update();
http://jsfiddle.net/noppanit/x0bdq3aa/
The event you are looking for is 'pressup', you may also need 'mouseleave'and 'mouseout'.
Strangely, this easeljs tutorial explicitly says that you can use the 'mouseup' event as you just did.
However, when you look to the docs about events attached to the Stage class and the ones attached to the DisplayObject class, there is no mention of this 'mouseup'.
About the 'pressup' event :
After a mousedown occurs on a display object, a pressup event will be generated on that object when that mouse press is released. This can be useful for dragging and similar operations.
var stage = new createjs.Stage("demoCanvas");
var rect = new createjs.Shape();
rect.graphics.beginFill("#000").drawRect(0, 20, 200, 50);
rect.on('mousedown', function (mousedownEvent) {
var startX = mousedownEvent.rawX;
snippet.log('mousedown');
});
rect.on('pressup', function(mouseupEvent) {
var stopX = mouseupEvent.rawX;
snippet.log('mouseup');
snippet.log(stopX);
});
stage.addChild(rect);
stage.update();
<script src="https://code.createjs.com/easeljs-0.8.1.min.js"></script>
<!-- Provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>
<canvas id="demoCanvas" width="500" height="70"></canvas>
Check this code once, Here you will get x and y position continously.
function writeMessage(canvas, message) {
var context = canvas.getContext('2d');
context.clearRect(0, 0, canvas.width, canvas.height);
context.font = '18pt Calibri';
context.fillStyle = 'white';
context.fillText(message, 10, 25);
}
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
var canvas = document.getElementById('demoCanvas');
var context = canvas.getContext('2d');
canvas.addEventListener('mousemove', function(evt) {
var mousePos = getMousePos(canvas, evt);
var message = 'Mouse position: ' + mousePos.x + ',' + mousePos.y;
writeMessage(canvas, message);
}, false);
check this fiddle-> http://jsfiddle.net/x0bdq3aa/3/
This is to get the mouse coordinates relative to Canvas,getMousePos() method which returns the mouse coordinates based on the position of the client mouse and the position of the canvas obtained from the getBoundingClientRect() method of the window object.