Canvas how to handle my canvas when it start on center screen - javascript

The canvas is in the center of the screen and when I add event click and call console.log(e.clientX, e.client.Y) it give e.g. 530, 483 but my shape is 50,50 from canvas.
how do i know i've click on shape not the canvas on the background.
let shapes:any = [];
shapes.push({ x:50, y:50, width: this.qrSize, height: this.qrSize, color:'lightgreen' })
let is_mouse_in_shape = function(x:any, y:any, shape:any){
let shape_left = shape.x;
let shape_right = shape.x + shape.width;
let shape_top = shape.y;
let shape_bottom = shape.y + shape.height;
console.log(x,y) // x = 415, y = 467
console.log(shape_left, shape_top) // x = 50, y = 50
if( x > shape_left && x < shape_right && y > shape_top && y > shape_bottom ){
return true;
}
return false; // It's return false
}
let mouse_down = function(event:any){
event.preventDefault();
startX = parseInt(event.clientX);
startY = parseInt(event.clientY);
console.log(event)
let index = 0;
for(let shape of shapes){
if(is_mouse_in_shape(startX, startY, shape)){
console.log('yes');
current_shape_index = index;
} else {
console.log('no')
}
index++;
}
}
let draw_shapes = function(){
context.clearRect(0,0, canvas_width, canvas_height);
for (let shape of shapes){
context.fillStyle = shape.color;
context.fillRect(shape.x, shape.y, shape.width, shape.height);
}
}
draw_shapes();
canvas.onmousedown = mouse_down;

event.clientX and clientY give you the click position relative to the top-left of the window.
To get the click position relative to the top-left of the canvas, you have to subtract the canvas offset from it.
To do so, you can use canvas.getBoundingClientRect. You subtract its left value from clientX, and top from clientY before passing to the is_mouse_in_shape check.
Here's a working example. Note: I had to fix a small typo in the collision detection: y > shape_bottom should be y < shape_bottom.
const canvas = document.querySelector("canvas");
const context = canvas.getContext("2d");
const canvas_width = canvas.width;
const canvas_height = canvas.height;
let shapes = [];
shapes.push({ x:50, y:50, width: 30, height: 30, color:'lightgreen' })
let is_mouse_in_shape = function(x, y, shape){
let shape_left = shape.x;
let shape_right = shape.x + shape.width;
let shape_top = shape.y;
let shape_bottom = shape.y + shape.height;
console.log(x,y) // x = 415, y = 467
console.log(shape_left, shape_top) // x = 50, y = 50
if( x > shape_left && x < shape_right && y > shape_top && y < shape_bottom ){
return true;
}
return false; // It's return false
}
let mouse_down = function(event){
event.preventDefault();
const { left, top } = canvas.getBoundingClientRect();
startX = parseInt(event.clientX) - left;
startY = parseInt(event.clientY) - top;
let index = 0;
for(let shape of shapes){
if(is_mouse_in_shape(startX, startY, shape)){
console.log('yes');
current_shape_index = index;
} else {
console.log('no')
}
index++;
}
}
let draw_shapes = function(){
context.clearRect(0,0, canvas_width, canvas_height);
for (let shape of shapes){
context.fillStyle = shape.color;
context.fillRect(shape.x, shape.y, shape.width, shape.height);
}
}
draw_shapes();
canvas.onmousedown = mouse_down;
canvas {
margin-top: 23px;
margin-left: 123px;
border: 2px solid purple;
}
<canvas width="300" height="300"></canvas>

Related

Movable selection on a canvas

Here below is how to draw a "selection rectangle" on a <canvas> with drag-and-drop, see How to draw a selection rectangle with drag and drop on a HTML canvas?.
Is there a simple way to detect the selection rectangle on hover at a distance of a few pixels, and allow to move the selection rectangle with drag-and-drop?
var c1 = document.getElementById("c1"), c2 = document.getElementById("c2");
var ctx1 = c1.getContext("2d"), ctx2 = c2.getContext("2d");
ctx2.setLineDash([5, 5]);
var origin = null;
window.onload = () => { ctx1.drawImage(document.getElementById("img"), 0, 0); }
c2.onmousedown = e => { origin = {x: e.offsetX, y: e.offsetY}; };
window.onmouseup = e => { origin = null; };
c2.onmousemove = e => {
if (!!origin) {
ctx2.strokeStyle = "#ff0000";
ctx2.clearRect(0, 0, c2.width, c2.height);
ctx2.beginPath();
ctx2.rect(origin.x, origin.y, e.offsetX - origin.x, e.offsetY - origin.y);
ctx2.stroke();
}
};
#img { display: none; }
#canvas-container { position: relative; }
canvas { position: absolute; left: 0; top: 0; }
#c1 { z-index: 0; }
#c2 { z-index: 1; }
<img id="img" src="https://i.imgur.com/okSIKkW.jpg">
<div id="canvas-container">
<canvas id="c1" height="200" width="200"></canvas>
<canvas id="c2" height="200" width="200"></canvas>
</div>
Storing the current selection
To be able to move an existing selection, you have to save its state. Right now, your code "forgets" about it after drawing it once.
You can save your selection in a variable on mouseup like so:
const dx = origin.x - mouse.x;
const dy = origin.y - mouse.y;
selection = {
left: Math.min(mouse.x, origin.x),
top: Math.min(mouse.y, origin.y),
width: Math.abs(dx),
height: Math.abs(dy)
}
Intersection check
Your selection is a rectangle. You can check whether the mouse is intersecting the rectangle like so:
const intersects = (
mouse.x >= selection.left &&
mouse.x <= selection.left + selection.width &&
mouse.y >= selection.top &&
mouse.y <= selection.top + selection.height
);
If you want to add some padding around the rectangle, you can change the checks to be, for example, mouse.x >= selection.left - PADDING.
Make or Move
You now have to support 2 types of interactions:
Making new selections, and
Moving existing selections
This is where my implementation gets a bit messy, but you can probably refactor it yourself 🙂
I didn't change much in the making-selections code, other than saving the selection to a variable.
When moving selections, you take the dx and dy of your mouse drag and add them to the selection's original position (ox, oy):
const dx = origin.x - mouse.x;
const dy = origin.y - mouse.y;
selection.left = ox - dx;
selection.top = oy - dy;
Here's everything in a runnable snippet:
var c1 = document.getElementById("c1"),
c2 = document.getElementById("c2");
var ctx1 = c1.getContext("2d"),
ctx2 = c2.getContext("2d");
ctx2.setLineDash([5, 5]);
var origin = null;
let selection = null;
let selectionHovered = false;
let interaction = null;
let ox = null;
let oy = null;
window.onload = () => { ctx1.drawImage(document.getElementById("img"), 0, 0); }
c2.onmousedown = e => {
origin = {x: e.offsetX, y: e.offsetY};
if (selectionHovered) {
interaction = "MOVE_SELECTION";
ox = selection.left;
oy = selection.top;
} else {
interaction = "MAKE_SELECTION";
}
};
window.onmouseup = e => {
interaction = null;
origin = null;
};
c2.onmousemove = e => {
const x = e.offsetX;
const y = e.offsetY;
if (!interaction) {
selectionHovered = (
selection &&
x >= selection.left &&
x <= selection.left + selection.width &&
y >= selection.top &&
y <= selection.top + selection.height
);
} else {
const dx = origin.x - x;
const dy = origin.y - y;
// Update
switch (interaction) {
case "MOVE_SELECTION":
selection.left = ox - dx;
selection.top = oy - dy;
break;
case "MAKE_SELECTION":
selection = {
left: Math.min(x, origin.x),
top: Math.min(y, origin.y),
width: Math.abs(dx),
height: Math.abs(dy)
}
break
default:
// Do nothing
}
// Set selectionHovered
if (selection) {
} else {
selectionHovered = false;
}
}
// Draw
if (selection) drawSelection(selection);
};
function drawSelection({ top, left, width, height }) {
// Draw rect
ctx2.strokeStyle = "#ff0000";
ctx2.clearRect(0, 0, c2.width, c2.height);
ctx2.beginPath();
ctx2.rect(left, top, width, height);
ctx2.stroke();
// Set mouse
c2.style.cursor = selectionHovered ? "move" : "default";
}
#img { display: none; }
body { margin: 0; }
#canvas-container { position: relative; }
canvas { position: absolute; left: 0; top: 0; }
#c1 { z-index: 0; }
#c2 { z-index: 1; }
<img id="img" src="https://i.imgur.com/okSIKkW.jpg">
<div id="canvas-container">
<canvas id="c1" height="200" width="200"></canvas>
<canvas id="c2" height="200" width="200"></canvas>
</div>

Bullets follows mouse position

Im making simple arena shooter in JS and HTML.
right now I wanted to add shooting mechanic,I thought i would use code from my enemy class with bits of tweaking
here:
//differences between objects
let dirx = mouse.x - player.x,
diry = mouse.y - player.y;
//normalizing
let dist = Math.sqrt(dirx * dirx + diry * diry);
dirx = dirx / dist;
diry = diry / dist;
this.x += dirx * 5;
this.y += diry * 5;
Since my player is moving the player.x& player.y coords in dirX & dirY will change, meaning bullet wont go to original coords.
So I would be pleased for some help.
You could use vectors to determine the trajectory of the bullets.
In the example below, when I fire a bullet:
Initialize the position at the source of the bullet
The speed is determined by:
Subtracting the mouse position from the source
Normalizing the distance
Applying a speed constant
class Bullet {
constructor(source, target, created) {
this.position = source.clone();
this.speed = this.position.clone()
.subtract(Victor.fromObject(target))
.normalize()
.multiply(new Victor(-2, -2));
this.size = 3;
this.timeLeft = created + 500;
}
update() {
this.position = this.position.add(this.speed);
}
draw(ctx) {
ctx.fillStyle = 'yellow';
ctx.beginPath();
ctx.arc(this.position.x, this.position.y, this.size / 2, 0, 2 * Math.PI);
ctx.fill();
}
}
Note: I also added a timeLeft variable to remove the bullet from the game after a set period of time e.g. 500ms.
Demo
Here is an example using the vector logic explained above.
Controls
W (Up) - Move up
A (Left) - Move left
S (Down) - Move down
D (Right) - Move right
Mouse 1 - Hold to fire
const VK_W = 87;
const VK_A = 65;
const VK_S = 83;
const VK_D = 68;
const VK_UP = 38;
const VK_DOWN = 40;
const VK_LEFT = 37;
const VK_RIGHT = 39;
const canvas = document.querySelector('.game'),
stateBtn = document.querySelector('.state-btn');
let game;
const main = () => {
stateBtn.addEventListener('click', changeState);
const ctx = canvas.getContext('2d');
game = new Game(ctx, { width: 400, height: 300 });
game.run();
};
const changeState = (e) => {
const btn = e.currentTarget, running = btn.dataset.running === 'true';
if (running) {
game.pause();
} else {
game.run();
}
btn.textContent = running ? 'Pause' : 'Resume';
btn.dataset.running = !running;
};
class Game {
constructor(ctx, options) {
const { width, height } = options;
this.lastRender = 0;
this.ctx = ctx;
this.state = { keySet: new Set() };
this.bullets = [];
Object.assign(ctx.canvas, { width, height });
const origin = new Victor(width / 2, height / 2);
this.player = new Player({
name: 'Bob',
position: origin
});
ctx.canvas.addEventListener('mousemove', (e) => this.followMouse(e));
ctx.canvas.addEventListener('mousedown', (e) => this.mouseDown(e));
ctx.canvas.addEventListener('mouseup', (e) => this.mouseUp(e));
document.addEventListener('keydown', (e) => this.addKey(e), false);
document.addEventListener('keyup', (e) => this.removeKey(e), false);
}
followMouse(e) {
this.state.mousePos = getMousePos(e.currentTarget, e);
}
mouseDown(e) {
this.state.mouseDown = true;
}
mouseUp(e) {
this.state.mouseDown = false;
}
addKey(e) {
const key = e.which || e.keyCode || 0;
this.state.keySet.add(key);
}
removeKey(e) {
const key = e.which || e.keyCode || 0;
this.state.keySet.delete(key);
}
update(progress) {
const ks = this.state.keySet;
const x = (ks.has(VK_D) || ks.has(VK_RIGHT))
? 1 : (ks.has(VK_A) || ks.has(VK_LEFT)) ? -1 : 0;
const y = (ks.has(VK_S) || ks.has(VK_DOWN))
? 1 : (ks.has(VK_W) || ks.has(VK_UP)) ? -1 : 0;
this.player.position.add(new Victor(x, y));
this.bullets.forEach((bullet, index) => {
if (this.lastRender > bullet.timeLeft) {
this.bullets.splice(index, 1);
}
bullet.update(this.lastRender);
});
if (this.state.mousePos && this.state.mouseDown) {
this.bullets.push(new Bullet(this.player.position,
this.state.mousePos, this.lastRender));
}
}
draw() {
this.ctx.clearRect(0, 0, this.ctx.canvas.width, this.ctx.canvas.height);
this.player.draw(this.ctx);
this.bullets.forEach(bullet => bullet.draw(this.ctx));
}
run(timestamp) {
const progress = timestamp - this.lastRender;
this.update(progress);
this.draw();
this.lastRender = timestamp;
this.req = window.requestAnimationFrame((t) => this.run(t));
}
pause() {
const { width, height } = this.ctx.canvas;
this.ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
this.ctx.fillRect(0, 0, width, height);
this.ctx.font = '32px Arial';
this.ctx.fillStyle = '#FFF';
this.ctx.textAlign = 'center';
this.ctx.textBaseline = 'middle';
this.ctx.fillText('Paused', width / 2, height / 2);
cancelAnimationFrame(this.req);
this.req = null;
}
isRunning() {
return this.req !== null;
}
}
class Player {
constructor(options) {
const opts = { ...Player.defaultOptions, ...options };
this.name = opts.name;
this.position = opts.position;
this.size = opts.size;
}
draw(ctx) {
ctx.fillStyle = '#00FF00';
ctx.fillRect(this.position.x - this.size / 2,
this.position.y - this.size / 2, this.size, this.size);
}
};
Player.defaultOptions = {
size: 10,
position: new Victor(0, 0)
};
class Bullet {
constructor(source, target, created) {
this.position = source.clone();
this.speed = this.position.clone()
.subtract(Victor.fromObject(target))
.normalize()
.multiply(new Victor(-2, -2));
this.size = 3;
this.timeLeft = created + 500;
}
update() {
this.position = this.position.add(this.speed);
}
draw(ctx) {
ctx.fillStyle = 'yellow';
ctx.beginPath();
ctx.arc(this.position.x, this.position.y, this.size / 2, 0, 2 * Math.PI);
ctx.fill();
}
}
const getMousePos = (canvas, event) =>
(({ top, left }) => ({
x: event.clientX - left,
y: event.clientY - top
}))(canvas.getBoundingClientRect());
main();
.game {
background: #111;
}
.as-console-wrapper { max-height: 4em !important; }
<script src="https://cdnjs.cloudflare.com/ajax/libs/victor/1.1.0/victor.min.js"></script>
<canvas class="game"></canvas>
<div class="controls">
<button class="state-btn" data-running="true">Pause</button>
</div>

How to calculate the position of a click on a draggable canvas element?

I need help with a pretty difficult problem. I am currently making a game with React and Redux. In this game I use a canvas to create a map data from my redux store. Currently the map is just a matrix of black and white squares. Let's say that I wanted to change the color of a square when you click on it, but also maintain the ability to drag the element. The problem is that it is difficult to pinpoint exactly where the mouse is clicking given that the element can be dragged anywhere on the page. As far as I can tell, none of the mouseclick event object properties seem to be able to tell me. I thought offsetX and offsetY would tell me, but they don't seem to stay the same when the canvas object moves for some reason.
I am using React and Redux for this project, and the CanvasMap element is wrapped in a Draggable from this library: https://www.npmjs.com/package/react-draggable#draggablecore
import React from 'react'
import { connect } from 'react-redux'
import './CanvasMap.css'
class CanvasMap extends React.Component{
componentDidMount() {
const map = this.props.map //Data representing the map
const canvas = this.refs.canvas
const context = canvas.getContext('2d')
//Building the map on the canvas
for(let i = 0; i < map.length; i++){
for(let j = 0; j < map[i].length; j++){
const x=i*100
const y=j*100
const isBlackSquare= map[i][j] === 'black' ? true : false
if(isBlackSquare) context.fillRect(x, y, 100, 100)
else context.strokeRect(x, y, 100, 100)
}
}
function handleClick(e){
//None of the event properties seem to stay the same when the canvas is moved
console.log(e)
}
canvas.addEventListener('click', handleClick)
}
render(){
return (
<div className='Map'>
<canvas ref='canvas' width={8000} height={8000} />
</div>
)
}
}
function mapStateToProps(state){
return {
map: [...state.map]
}
}
const connectedComponent = connect(mapStateToProps)(CanvasMap)
export { connectedComponent as CanvasMap }
In most cases when you click on an HTML element you can use the rectangleBounding Box and get coordinators from that like
domRect = element.getBoundingClientRect();
in a canvas click position it is a little more difficult
Here is a script I did a while ago to draw while dragging the mouse the on the canvas .Maybe you can apply this method
<html>
<head>
<style>
* { margin:0; padding:0; } /* to remove the top and left whitespace */
html, body { width:100%; height:100%; } /* just to be sure these are full screen*/
canvas { display:block; } /* To remove the scrollbars */
</style>
</head>
<body>
<canvas id="canvas" ></canvas>
<script>
////////////////////////////////////////
(function() {
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var elemLeft = canvas.offsetLeft;
var elemTop = canvas.offsetTop;
var BB=canvas.getBoundingClientRect();
var offsetX=BB.left;
var offsetY=BB.top;
// resize the canvas to fill browser window dynamically
window.addEventListener('resize', resizeCanvas, false);
function resizeCanvas() {
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
/**
* Your drawings need to be inside this function otherwise they will be reset when
* you resize the browser window and the canvas goes will be cleared.
*/
drawStuff();
}
resizeCanvas();
function drawStuff() {
// do your drawing stuff here
var img = new Image();
img.src = 'images/3PkBe.gif';
img.onload = function()
{
//var canvas = document.getElementById('canvas');
// create pattern
var ptrn = ctx.createPattern(img, 'repeat'); // Create a pattern with this image, and set it to "repeat".
ctx.fillStyle = ptrn;
ctx.fillRect(0, 0, canvas.width, canvas.height); // context.fillRect(x, y, width, height);
ctx.shadowBlur=20;
//ctx.shadowColor="black";
//ctx.fillStyle="green";
//ctx.fillRect(20,160,100,80);
ctx.strokeStyle = "lightgray";
//var canvasOffset = canvas.offset();
//var offsetX = canvasOffset.left;
//var offsetY = canvasOffset.top;
var mouseIsDown = false;
var lastX = 0;
var lastY = 0;
var elements = [];
makeShip( 30 , 30,120, 120, '#119' , "romea");
makeShip( 30, 160,120, 120, '#393', "fomar");
makeShip( 30, 290,120, 120, '#955', "ojab");
makeShip( 30, 420,120, 120, '#6ff', "eliot");
// Add event listener for `click` events.
canvas.addEventListener('click', function(event) {
var x = event.pageX - elemLeft,
y = event.pageY - elemTop;
console.info(x, y);
elements.forEach(function(element) {
if (y > element.y && y < element.y + element.height && x > element.x && x < element.x + element.width) {
console.log(element.name);
}
});
}, false);
canvas.addEventListener('mousedown', function(event) {
var x = event.pageX - elemLeft,
y = event.pageY - elemTop;
console.info(x, y);
elements.forEach(function(element) {
if (y > element.y && y < element.y + element.height && x > element.x && x < element.x + element.width) {
console.info(element.name);
handleMouseDown(element);
}
});
}, false);
canvas.addEventListener('mousemove', function(event) {
var x = event.pageX - elemLeft,
y = event.pageY - elemTop;
console.info(x, y);
elements.forEach(function(element) {
if (y > element.y && y < element.y + element.height && x > element.x && x < element.x + element.width) {
console.info(element.name);
handleMouseMove(element,x,y);
}
});
}, false);
canvas.addEventListener('mouseup', function(event) {
var x = event.pageX - elemLeft,
y = event.pageY - elemTop;
//console.info(x, y);
elements.forEach(function(element) {
//if (y > element.y && y < element.y + element.height && x > element.x && x < element.x + element.width) {
console.info(element.name + "mouse up evenr=========");
handleMouseUp(element);
//}
});
}, false);
function makeShip(x, y, width, height, colour,ShipName) {
var ship = {
name: ShipName,
colour: colour,
width: width,
height: height,
x: x,
y: y
}
elements.push(ship);
return (ship);
}
function drawShip(ship) {
//ctx.fillStyle = ship.colour;
//ctx.fillRect(ship.x, ship.y, ship.width, ship.height);
//ctx.fillRect(element.x, element.y, element.width, element.height);
}
function drawAllShips() {
// ctx.clearRect(0, 0, canvas.width, canvas.height);
for (var i = 0; i < elements.length; i++) {
var ship = elements[i]
//drawShip(ship);
ctx.fillStyle = ship.colour;
ctx.fillRect(ship.x , ship.y, ship.width, ship.height);
// ctx.fillStyle = ship.fill;
// ctx.fill();
// ctx.stroke();
}
}
// Add element.
//elements.push({
//colour: '#05EFFF',
//width: 150,
//height: 100,
//x: 20,
//y: 15
//});
// Render elements.
// elements.forEach(function(element) {
// ctx.fillStyle = element.colour;
// ctx.fillRect(element.x, element.y, element.width, element.height);
// });
drawAllShips();
function handleMouseDown(e) {
mouseX = e.x ;
mouseY = e.y ;
//mouseX = parseInt(e.x - offsetX);
//mouseY = parseInt(e.y - offsetY);
console.log("===========Problem "+mouseX);
// mousedown stuff here
lastX = mouseX;
lastY = mouseY;
mouseIsDown = true;
//alert("mouse Handle");
}
function handleMouseUp(e) {
//mouseX = parseInt(e.clientX - offsetX);
//mouseY = parseInt(e.clientY - offsetY);
ctx.onmousemove = null;
// mouseup stuff here
mouseIsDown = false;
return
}
function handleMouseMove(e,x,y) {
if (mouseIsDown) {
//console.log(' no fuck');
mouseX = e.x ;
mouseY = e.y ;
console.log(e.name+"is truing to drag");
// mousemove stuff here
//for (var i = 0; i < elements.length; i++) {
//if (ctx.isPointInPath(mouseX, mouseY)) {
//console.log('============== no fuck');
var ship =e;// elements[i];
ship.x = x-15;//(mouseX - lastX);
ship.y = y-20;//(mouseY -lastY);
// ship.right = ship.x + ship.width;
// ship.bottom = ship.y + ship.height;
//drawShip(ship);
//}
//}
lastX = mouseX;
lastY = mouseY;
drawAllShips();
}
}
<!-- ctx.mousedown(function (e) { -->
<!-- handleMouseDown(e); -->
<!-- }); -->
<!-- ctx.mousemove(function (e) { -->
<!-- handleMouseMove(e); -->
<!-- }); -->
<!-- ctx.mouseup(function (e) { -->
<!-- handleMouseUp(e); -->
<!-- }); -->
}
}
})();
</script>
</body>
</html>
SOLVED IT!
I got lost in the slew of data around elements and click events, I was trying to figure out the right combination of pageX, clientX, offsetLeft, screenX, etc. However, the final solution is incredibly simple once you know exactly what to do. Here it is:
function handleClick(e){
const rect = e.target.getBoundingClientRect()
const x = e.pageX - rect.left
const y = e.pageY - rect.top
}
This should get you the exact x and y coordinate of your mouse in relation to the element, no matter where you drag and reposition the element.

html5 canvas tooltip only visible for last drawn object, not for previous ones

what exactly I want to achieve is
to draw objects on canvas and
on mouseover display relevant data in tooltip.
here you can view the code.
var canvasBack;
var canvasLabel;
var canvasDraw;
var ctxBack;
var ctxLabel;
var ctxDraw;
var last_mousex = 0;
var last_mousey = 0;
var mousex = 0;
var mousey = 0;
var canWidth;
var canHeight;
var scaleParameter;
var radius;
var xVertex;
var yVertex;
var hotspots = [];
// initialization on loading of canvas
$('canvas').ready(function() {
init();
});
// initialization function used for binding events, and inital logic implemented.
function init() {
scaleParameter = 1;
canvasBack = document.getElementById('backSpace');
canvasLabel = document.getElementById('layerCanvas');
canvasDraw = document.getElementById('drawSpace');
ctxBack = canvasBack.getContext('2d');
ctxLabel = canvasLabel.getContext('2d');
ctxDraw = canvasDraw.getContext('2d');
canWidth = parseInt($(canvasBack).attr('width'));
canHeight = parseInt($(canvasBack).attr('height'));
var canvasx = $(canvasBack).offset().left;
var canvasy = $(canvasBack).offset().top
var mousedown = false;
//Mousedown
$('canvas').on('mousedown', function(e) {
$('#drawSpace').css('display', 'block');
last_mousex = mousex = parseInt(e.clientX - canvasx);
last_mousey = mousey = parseInt(e.clientY - canvasy);
mousedown = true;
});
//Mouseup
$('canvas').on('mouseup', function(e) {
hotspots.push({
x: xVertex,
y: yVertex,
radius: radius,
tip: 'You are over ' + mousex + ',' + mousey
});
let cw = canvasBack.width;
let ch = canvasBack.height;
ctxBack.drawImage(canvasDraw, 0, 0, cw, ch);
$('#drawSpace').css('display', 'none');
mousedown = false;
});
//Mousemove
$('canvas').on('mousemove', function(e) {
mousex = parseInt(e.clientX - canvasx);
mousey = parseInt(e.clientY - canvasy);
if (mousedown) {
// draw(mousedown);
drawEllipse(last_mousex, last_mousey, mousex, mousey);
} else {
hoverTooltip();
}
});
}
function drawEllipse(x1, y1, x2, y2) {
var leftScroll = $("#scrollParent").scrollLeft();
var topScroll = $("#scrollParent").scrollTop();
let cw = canvasBack.width;
let ch = canvasBack.height;
ctxDraw.clearRect(0, 0, cw, ch);
var radiusX = x2 - x1,
radiusY = y2 - y1,
centerX = x1 + radiusX,
centerY = y1 + radiusY,
step = 0.01,
a = step,
pi2 = Math.PI * 2 - step;
radius = Math.sqrt(radiusX * radiusX + radiusY * radiusY) / 2;
ctxDraw.beginPath();
ctxDraw.arc(centerX, centerY, radius, 0, 2 * Math.PI, true);
ctxDraw.closePath();
ctxDraw.fillStyle = 'green';
ctxDraw.fill();
ctxDraw.strokeStyle = '#000';
ctxDraw.stroke();
xVertex = centerX;
yVertex = centerY;
}
// tooltip show on hover over objects
function hoverTooltip() {
var leftScroll = $("#scrollParent").scrollLeft();
var topScroll = $("#scrollParent").scrollTop();
let cw = canvasBack.width;
let ch = canvasBack.height;
for (var i = 0; i < hotspots.length; i++) {
var h = hotspots[i];
var dx = mousex - h.x;
var dy = mousey - h.y;
if (dx * dx + dy * dy < h.radius * h.radius) {
$('#console').text(h.tip);
ctxLabel.clearRect(0, 0, cw, ch);
ctxLabel.fillText(h.tip, mousex + leftScroll, mousey + topScroll);
} else {
ctxLabel.clearRect(0, 0, cw, ch);
}
}
}
#scrollParent {
width: 644px;
height: 364px;
overflow: auto;
position: relative;
}
#scrollParent>canvas {
position: absolute;
left: 0;
top: 0;
border: 1px solid #ababab;
}
#backSpace {
z-index: 0;
}
#drawSpace {
display: none;
z-index: 1;
}
#layerCanvas {
z-index: 2;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="scrollParent">
<!-- actual canvas that is visible -->
<canvas width="640" height="360" id="backSpace"></canvas>
<!-- canvas used for drawing new objects -->
<canvas width="640" height="360" id="drawSpace"></canvas>
<!-- canvas used to display tooltip -->
<canvas width="640" height="360" id="layerCanvas"></canvas>
</div>
<div id="console"></div>
</div>
actual problem is in the bellow image, tooltip worked fine when the 1st object was drawn, but once the second object was drawn tooltip worked only for the second one, not for previously drawn objects.
what is causing this issue, and how to fix it ?
Removing else will not remove the label when leaving the elipse.
You need to exit the loop once you found the correct elipse from the array using break.
function hoverTooltip() {
var leftScroll = $("#scrollParent").scrollLeft();
var topScroll = $("#scrollParent").scrollTop();
let cw = canvasBack.width;
let ch = canvasBack.height;
for (var i = 0; i < hotspots.length; i++) {
var h = hotspots[i];
var dx = mousex - h.x;
var dy = mousey - h.y;
if (dx * dx + dy * dy < h.radius * h.radius) {
$('#console').text(h.tip);
ctxLabel.clearRect(0, 0, cw, ch);
ctxLabel.fillText(h.tip, mousex + leftScroll, mousey + topScroll);
break; // exit the loop
} else {
ctxLabel.clearRect(0, 0, cw, ch);
}
}
}
UPDATE
I figured that if you draw two objects over each other, it will behave poorly. Try this instead. It will display information of the latest drawn spot.
function hoverTooltip() {
var leftScroll = $("#scrollParent").scrollLeft();
var topScroll = $("#scrollParent").scrollTop();
let cw = canvasBack.width;
let ch = canvasBack.height;
var spots = hotspots.filter((h) => {
var dx = mousex - h.x;
var dy = mousey - h.y;
return (dx * dx + dy * dy < h.radius * h.radius);
})
if (spots.length > 0) {
var h = spots[spots.length - 1]; // latest drawn spot
$('#console').text(h.tip);
ctxLabel.clearRect(0, 0, cw, ch);
ctxLabel.fillText(h.tip, mousex + leftScroll, mousey + topScroll);
}
else
{
ctxLabel.clearRect(0, 0, cw, ch);
}
}
I see there are already a few answers. This is mine:
In order to be able to show the label for every circle on hover you need to save all your circles in am array: the circles array. I'm using the ctx.isPointInPath() method to know if the mouse is over the circle, and if it is I paint the label.
const canvas = document.querySelector("canvas");
const ctx = canvas.getContext("2d");
let cw = canvas.width = 640;
let ch = canvas.height = 360;
let found = false;//is a circle found?
const cText = document.querySelector("#text");
const ctxText = cText.getContext("2d");
cText.width = 640;
cText.height = 360;
ctxText.font="1em Verdana";
let drawing = false;
let circles = []
class Circle{
constructor(x,y){
this.x = x;
this.y = y;
this.r = 0;
}
updateR(m) {
this.r = dist(this,m);
}
draw(){
ctx.beginPath();
ctx.arc(this.x,this.y,this.r,0,2*Math.PI);
}
paint(){
ctx.fillStyle = "green";
ctx.strokeStyle = "black";
this.draw();
ctx.stroke();
ctx.fill();
}
label(m){
this.draw();
if (ctx.isPointInPath(m.x, m.y)) {
ctx.beginPath();
ctx.arc(this.x, this.y, 4, 0, 2 * Math.PI);
ctxText.fillStyle = "black";
ctxText.fillText(`you are over ${this.x},${this.y}`,m.x,m.y)
found = true;
}
}
}
let m = {}// mouse
cText.addEventListener("mousedown",(e)=>{
drawing = true;
m = oMousePos(canvas, e);
let circle = new Circle(m.x,m.y)
circles.push(circle);
})
cText.addEventListener("mouseup",(e)=>{
drawing = false;
})
cText.addEventListener("mousemove",(e)=>{
m = oMousePos(canvas, e);
found = false;
if(drawing){
let circle = circles[circles.length-1];//the last circle in the circles arrey
circle.updateR(m);
}
ctx.clearRect(0,0, cw,ch);
ctxText.clearRect(0,0,cw,ch)
circles.map((c) => {c.paint();});
for(let i = circles.length-1; i >=0 ; i--){
circles[i].label(m);
if(found){break;}
}
})
function oMousePos(canvas, evt) {
var ClientRect = canvas.getBoundingClientRect();
return { //objeto
x: Math.round(evt.clientX - ClientRect.left),
y: Math.round(evt.clientY - ClientRect.top)
}
}
function dist(p1, p2) {
let dx = p2.x - p1.x;
let dy = p2.y - p1.y;
return Math.sqrt(dx * dx + dy * dy);
}
canvas{border:1px solid;position:absolute; top:0; left:0;}
#scrollParent{position:relative;}
<div id="scrollParent">
<!-- actual canvas that is visible -->
<canvas width="640" height="360"></canvas>
<canvas width="640" height="360" id="text"></canvas>
</div>
I've updated the code in base of the comment of #HelderSepu
A SECOND UPDATE in base of a second message from #HelderSepu. He wants to see "multiple message but avoid overlapping the messages"
const canvas = document.querySelector("canvas");
const ctx = canvas.getContext("2d");
let cw = canvas.width = 640;
let ch = canvas.height = 360;
let text = "";
const cText = document.querySelector("#text");
const ctxText = cText.getContext("2d");
cText.width = 640;
cText.height = 360;
ctxText.font="1em Verdana";
let drawing = false;
let circles = []
class Circle{
constructor(x,y){
this.x = x;
this.y = y;
this.r = 0;
}
updateR(m) {
this.r = dist(this,m);
}
draw(){
ctx.beginPath();
ctx.arc(this.x,this.y,this.r,0,2*Math.PI);
}
paint(){
ctx.fillStyle = "green";
ctx.strokeStyle = "black";
this.draw();
ctx.stroke();
ctx.fill();
}
label(m){
this.draw();
if (ctx.isPointInPath(m.x, m.y)) {
this.text = `[${this.x},${this.y}]`
}else{
this.text = "";
}
}
}
let m = {}// mouse
cText.addEventListener("mousedown",(e)=>{
drawing = true;
m = oMousePos(canvas, e);
let circle = new Circle(m.x,m.y)
circles.push(circle);
})
cText.addEventListener("mouseup",(e)=>{
drawing = false;
})
cText.addEventListener("mousemove",(e)=>{
m = oMousePos(canvas, e);
if(drawing){
let circle = circles[circles.length-1];//the last circle in the circles arrey
circle.updateR(m);
}
ctx.clearRect(0,0, cw,ch);
ctxText.clearRect(0,0,cw,ch);
text="";
circles.map((c) => {c.paint();c.label(m);});
circles.map((c) => {text += c.text;});
ctxText.fillStyle = "black";
ctxText.fillText(text,m.x,m.y)
})
function oMousePos(canvas, evt) {
var ClientRect = canvas.getBoundingClientRect();
return { //objeto
x: Math.round(evt.clientX - ClientRect.left),
y: Math.round(evt.clientY - ClientRect.top)
}
}
function dist(p1, p2) {
let dx = p2.x - p1.x;
let dy = p2.y - p1.y;
return Math.sqrt(dx * dx + dy * dy);
}
canvas{border:1px solid;position:absolute; top:0; left:0;}
#scrollParent{position:relati
<div id="scrollParent">
<!-- actual canvas that is visible -->
<canvas width="640" height="360"></canvas>
<canvas width="640" height="360" id="text"></canvas>
<div id="console"></div>
</div>

JavaScript Canvas on draw vanishes

I have a canvas function which draws a square if I click on the canvas field and move the mouse, that works so far.
My Problem is that if I release the mouse and click at the canvas again the old drawn rectangle vanishes.
How do I make it possible that the old drawn does not get vanished.
My function:
function foo() {
var tool = this;
this.started = false;
var canvasx = canvas.offsetLeft;
var canvasy = canvas.offsetTop;
var last_mousex = 0;
var last_mousey = 0;
var mousex = 0;
var mousey = 0;
this.mousedown = function (ev) {
if(checkboxSquare.checked) {
last_mousex = parseInt(ev.clientX-canvasx);
last_mousey = parseInt(ev.clientY-canvasy);
context.strokeStyle = $('#selectColor').val();
context.lineWidth = $('#selectWidth').val();
tool.started = true;
}
};
this.mousemove = function (ev) {
if (tool.started && checkboxSquare.checked) {
mousex = parseInt(ev.clientX-canvasx);
mousey = parseInt(ev.clientY-canvasy);
context.clearRect(0, 0, canvas.width, canvas.height); // clear canvas
context.beginPath();
var width = mousex-last_mousex;
var height = mousey-last_mousey;
context.rect(last_mousex,last_mousey,width,height);
context.stroke();
}
};
this.mouseup = function (ev) {
if (tool.started && checkboxSquare.checked) {
tool.mousemove(ev);
tool.started = false;
}
};
}
It Looks something like this: http://jsfiddle.net/AbdiasSoftware/kqW4X/
The old drawn rectangle vanishes on click because, you are clearing the entire canvas each time before drawing a rectangle.
The easiest workaround would be to save the entire canvas as an image on mouseup and draw that image before drawing each rectangle.
var canvas;
var _foo = new foo();
canvas.onmousedown = _foo.mousedown;
canvas.onmousemove= _foo.mousemove;
canvas.onmouseup = _foo.mouseup;
function foo() {
canvas = $('#canvas')[0];
var context = canvas.getContext('2d');
var checkboxSquare = $('#checkboxSquare')[0];
var img = new Image();
var tool = this;
this.started = false;
var last_mousex = 0;
var last_mousey = 0;
var mousex = 0;
var mousey = 0;
this.mousedown = function (ev) {
if(checkboxSquare.checked) {
last_mousex = ev.offsetX;
last_mousey = ev.offsetY;
context.strokeStyle = $('#selectColor').val();
context.lineWidth = $('#selectWidth').val();
tool.started = true;
}
};
this.mousemove = function (ev) {
if (tool.started && checkboxSquare.checked) {
mousex = ev.offsetX;
mousey = ev.offsetY;
context.clearRect(0, 0, canvas.width, canvas.height); // clear canvas
context.drawImage(img, 0, 0); // draw saved canvas (image)
context.beginPath();
var width = mousex-last_mousex;
var height = mousey-last_mousey;
context.rect(last_mousex,last_mousey,width,height);
context.stroke();
}
};
this.mouseup = function (ev) {
if (tool.started && checkboxSquare.checked) {
tool.mousemove(ev);
img.src = canvas.toDataURL(); // save canvas as image
tool.started = false;
}
};
}
canvas {
border: 1px solid black;
cursor: default;
margin-top: 5px
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" id="checkboxSquare">Square | Color
<select id="selectColor">
<option value="red">red</option>
<option value="green">green</option>
<option value="blue">blue</option>
</select> | Width
<select id="selectWidth">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<canvas id="canvas" width="400" height="400"></canvas>
Just create a background canvas same as the main canvas. When you drag out a new box, first draw the background canvas (with all the past boxes) on the main canvas then the current box being drawn. When you finish dragging the box, just daw it to the background canvas.
const canvas = document.createElement("canvas");
const background = document.createElement("canvas");
canvas.style.border="2px solid black";
canvas.style.cursor = "crosshair";
background.width = canvas.width = innerWidth - 24;
background.height = canvas.height = innerHeight - 24;
const ctx = canvas.getContext("2d");
background.ctx = background.getContext("2d");
document.body.appendChild(canvas);
const bounds = canvas.getBoundingClientRect();
var currentBox;
const boxStyle = {
fillStyle : "#4aF",
strokeStyle : "black",
lineWidth : 3,
lineJoin : "round",
}
const mouse = { x : 0, y : 0,button : false, changed : false };
["mousemove","mousedown","mouseup"].forEach(en => document.addEventListener(en, mouseEvent));
function createBox(x,y,w,h,style){ return {x,y,w,h,style,draw : drawBox} }
function drawBox(ctx){
setStyle(ctx, this.style);
ctx.beginPath();
ctx.rect(this.x,this.y,this.w,this.h);
ctx.fill();
ctx.stroke();
}
function setStyle(ctx, style){ Object.keys(style).forEach(key => ctx[key] = style[key]) }
function mouseEvent(event) {
mouse.x = event.pageX - bounds.left - scrollX;
mouse.y = event.pageY - bounds.top - scrollY;
if(event.type === "mousedown"){ mouse.button = true }
else if(event.type === "mouseup"){ mouse.button = false }
mouse.changed = true;
}
function mainLoop(){
var b = currentBox; // alias for readability
if(mouse.changed){
if(mouse.button){
if(!b){
b = currentBox = createBox(mouse.x,mouse.y,0,0,boxStyle);
}else{
b.w = mouse.x - b.x;
b.h = mouse.y - b.y;
}
}else if(b){
b.draw(background.ctx);
b = currentBox = undefined;
}
if(b){
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.drawImage(background,0,0);
b.draw(ctx);
canvas.style.cursor = "none";
}else{
canvas.style.cursor = "crosshair";
}
mouse.changed = false;
}
requestAnimationFrame(mainLoop);
}
requestAnimationFrame(mainLoop);
Extra Note. Capture the mouse using the Document
When you create canvas drawing apps you should listen to the document mouse events rather than the canvas. When the mouse button is down the mouse is captured and will continue to send mouse events while the mouse is down, even if you have moved off the canvas, document, or event outside the browser window.
This means you can drag content of the canvas and not worry about losing the mouseup event.
Burn some time.
I have some time to burn so will extend the demo above to include selecting and moving existing boxes. Draw boxes as normal. Mouse over boxes will highlight them, click to select them. When selected can be dragged. Uses the same method background image to hold old boxes. But have added a box list to hold old boxes
A more extensive example
const canvas = document.createElement("canvas");
const background = document.createElement("canvas");
canvas.style.border="2px solid black";
canvas.style.cursor = "crosshair";
background.width = canvas.width = innerWidth - 24;
background.height = canvas.height = innerHeight - 24;
const ctx = canvas.getContext("2d");
background.ctx = background.getContext("2d");
document.body.appendChild(canvas);
const bounds = canvas.getBoundingClientRect();
var currentBox;
var selectedBox;
var mouseOverBox;
const styles = {
box : {
fillStyle : "#4aF",
strokeStyle : "black",
lineWidth : 3,
lineJoin : "round",
},
highlight : {
strokeStyle : "white",
lineWidth : 1,
lineJoin : "round",
setLineDash : [[10,10]],
},
selected : {
strokeStyle : "red",
lineWidth : 2,
lineJoin : "round",
setLineDash : [[5,5]],
},
}
const boxes = {
items : [],
add(box){ // add a box and fix width and height to positive
if(box.w < 0){
box.x += box.w;
box.w = -box.w;
}
if(box.h < 0){
box.y += box.h;
box.h = -box.h;
}
boxes.items.push(box)
},
apply(name, ...args){
for(var i = 0; i < boxes.items.length; i ++ ){
boxes.items[i][name](...args);
}
},
};
const mouse = { x : 0, y : 0,button : false, changed : false };
["mousemove","mousedown","mouseup"].forEach(en => document.addEventListener(en, mouseEvent));
const boxBehaviours = {
draw(ctx, style = this.style){
if(!this.hide){
setStyle(ctx, style);
ctx.beginPath();
ctx.rect(this.x,this.y,this.w,this.h);
if(style.fillStyle) { ctx.fill() }
if(style.strokeStyle) {ctx.stroke() }
}
},
isPointOver(x,y){
var b = this;
if(x >= b.x && x < b.x + b.w && y >= b.y && y < b.y + b.h){
b.mouseOver = true;
boxBehaviours.topMouseBox = b;
}else {
b.mouseOver =false;
}
},
}
function createBox(x,y,w,h,style){
return {x,y,w,h,style, ...boxBehaviours};
}
function setStyle(ctx, style){
Object.keys(style).forEach(key => {
if(typeof ctx[key] === "function"){
ctx[key](...style[key]);
}else{
ctx[key] = style[key];
}
})
}
function mouseEvent(event) {
mouse.x = event.pageX - bounds.left - scrollX;
mouse.y = event.pageY - bounds.top - scrollY;
if(event.type === "mousedown"){ mouse.button = true }
else if(event.type === "mouseup"){ mouse.button = false }
}
function redrawBackground(){
background.ctx.clearRect(0,0,canvas.width,canvas.height)
boxes.apply("draw",background.ctx);
}
function mainLoop(time){
var b = currentBox; // alias for readability
var mob = mouseOverBox; // alias for readability
var sb = selectedBox; // alias for readability
// first check mouse button. If button down could be
// dragging a selected box or creating a new box
if(mouse.button){
if(sb){ // is selected box
if(!mouse.drag){ // start the drag
mouse.drag = {x : mouse.x - sb.x, y : mouse.y - sb.y}
}else{ // move the box
sb.x = mouse.x- mouse.drag.x;
sb.y = mouse.y- mouse.drag.y;
}
}else{ // else muse be create (or select click)
if(!b){
b = currentBox = createBox(mouse.x,mouse.y,0,0,styles.box);
}else{
b.w = mouse.x - b.x;
b.h = mouse.y - b.y;
}
}
}else if(b || sb){ // mouse up and there is a box
if(sb){ // if selected box
if(mouse.drag){ // is dragging then drop it
mouse.drag = undefined;
sb.hide = false;
redrawBackground();
sb = selectedBox = undefined;
}
// is the mouse is down and has not moved over 2 pixels
// and there is a mob (mouseOverBox) under it
// then dump the new box and select the mob box
}else if(Math.abs(b.w) < 2 && Math.abs(b.h) < 2 && mob){
sb = selectedBox = mob;
mob = mouseOverBox = undefined;
b = currentBox = undefined;
sb.hide = true;
redrawBackground();
}else{
// just a normal box add it to box array
// draw it and remove it from currentBox
boxes.add(b);
b.draw(background.ctx);
b = currentBox = undefined;
}
}
// clear andf draw background
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.drawImage(background,0,0);
if(b){ // is there a current box then draw that
b.draw(ctx);
canvas.style.cursor = "none";
} else { // no current box so
// find any boxes under the mouse
boxBehaviours.topMouseBox = null;
boxes.apply("isPointOver",mouse.x, mouse.y);
// is there a selected box (sb)
if(sb){ // yes selected box then draw it
ctx.save();
styles.selected.lineDashOffset = time / 25;
sb.hide = false;
sb.draw(ctx,styles.selected);
sb.hide = true;
ctx.restore();
canvas.style.cursor = "move";
// no selected box sp then just high light the box under the
// mouse and assign it to mouseOverBox (mob);
}else if(boxBehaviours.topMouseBox){
mob = mouseOverBox = boxBehaviours.topMouseBox;
ctx.save();
styles.highlight.lineDashOffset = time / 20;
mob.draw(ctx, styles.highlight);
ctx.restore();
canvas.style.cursor = "pointer";
}else{
canvas.style.cursor = "crosshair";
}
}
requestAnimationFrame(mainLoop);
}
requestAnimationFrame(mainLoop);
var point = [];
var clicks = 0;
var sketch = document.querySelector('#sketch');
var sketch_style = getComputedStyle(sketch);
// Creating a tmp canvas
var tmp_canvas = document.createElement('canvas');
var tmp_ctx = tmp_canvas.getContext('2d');
tmp_canvas.id = 'tmp_canvas';
tmp_canvas.width = parseInt(sketch_style.getPropertyValue('width'));
tmp_canvas.height = parseInt(sketch_style.getPropertyValue('height'));
sketch.appendChild(tmp_canvas);
var canvas = document.createElement('canvas');
var context = canvas.getContext('2d');
canvas.id = 'paint';
canvas.width = parseInt(sketch_style.getPropertyValue('width'));
canvas.height = parseInt(sketch_style.getPropertyValue('height'));
sketch.appendChild(canvas);
tmp_canvas.addEventListener('mousedown', mousedown, false);
tmp_canvas.addEventListener('mousemove', mousemove, false);
tmp_canvas.addEventListener('mouseup', mouseup, false);
function mousemove(e) {
if (clicks == 1) {
x = e.layerX - this.offsetLeft;
y = e.layerY - this.offsetTop;
showRect(x, y);
}
}
function showRect(x, y) {
tmp_ctx.clearRect(0, 0, canvas.width, canvas.height); // clear canvas
tmp_ctx.beginPath();
var width = x - point[0].x;
var height = y - point[0].y;
tmp_ctx.rect(point[0].x, point[0].y, width, height);
tmp_ctx.stroke();
}
function mousedown(e) {
x = e.layerX - this.offsetLeft;
y = e.layerY - this.offsetTop;
point.push({
x,
y
});
clicks++;
};
function mouseup() {
context.drawImage(tmp_canvas, 0, 0);
clicks = 0;
point.length = 0;
}
html, body {
width: 100% ;
height: 100% ;
}
#sketch {
border: 10px solid gray;
height: 100% ;
position: relative;
}
#tmp_canvas {
position: absolute;
left: 0px;
right: 0;
bottom: 0;
top: 0;
cursor: crosshair;
}
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<div id="sketch">
</div>
</body>
</html>
Try to do in temporary canvas and redraw all in main.
jsfiddle:-https://jsfiddle.net/durga598/v0m06faz/
I'm assuming that the foo() function is being called for every frame, either through setInterval or requestAnimationFrame. If my assumption is right, the reason why your previously drawn square disappears is because you are only storing the x and y coordinates of one rectangle, and every time you click on the canvas again, it gets overwritten by the new values for the new rectangle.
To solve your problem, you should store the x and y coordinates as well as the dimensions of the square on mouseup. These coordinates can be stored in an array.
var squares = [];
this.mouseup = function (ev) {
// other code
var square = {
x: last_mousex,
y: last_mousey,
width: mousex - last_mousex,
height: mousey - last_mousey
};
squares.push(square);
};
Now every time you draw the square, draw the squares stored in the squares array first.
this.mousemove = function (ev) {
if (tool.started && checkboxSquare.checked) {
// other code
context.clearRect(0, 0, canvas.width, canvas.height); // clear canvas
// draw each square in the squares array after clearning the canvas
squares.forEach(function(square) {
context.beginPath();
context.rect(square.x, square.y, square.width, square.height);
});
context.beginPath();
var width = mousex - last_mousex;
var height = mousey - last_mousey;
context.rect(last_mousex, last_mousey, width, height);
context.stroke();
}
};
You'll see some code repetitions in drawing the squares, it's a good opportunity to abstract it into a separate function.

Categories