Get the mouse coordinates when clicking on canvas

问题

A common question, but I still need help. I'm trying to get and store the mouse coordinates when someone clicks within the canvas.

my HTML

<canvas id="puppyCanvas" width="500" height="500" style="border:2px solid black" onclick = "storeGuess(event)"></canvas>

and my javascript

//setup canvas
var canvasSetup = document.getElementById("puppyCanvas");
var ctx = canvasSetup.getContext("2d");

guessX = 0;//stores user's click on canvas
 guessY = 0;//stores user's click on canvas

function storeGuess(event){
    var x = event.clientX - ctx.canvas.offsetLeft;
    var y = event.clientY - ctx.canvas.offsetTop;
    /*guessX = x;
    guessY = y;*/


    console.log("x coords:" + x + ", y coords" + y);

I've read loads of forums, w3schools, and videos on this. I'm close to figuring it out, but I'm missing something. I can get the coordinates of the page if I delete the ctx.canvas.offsetLeft and ctx.canvas.offsetTop. But i need to incorporate those somehow to get the coordinates of the canvas, and then store then into the variables guessX and guessY.

回答1:

You could achieve that by using the offsetX and offsetY property of MouseEvent

//setup canvas
var canvasSetup = document.getElementById("puppyCanvas");
var ctx = canvasSetup.getContext("2d");
guessX = 0; //stores user's click on canvas
guessY = 0; //stores user's click on canvas
function storeGuess(event) {
    var x = event.offsetX;
    var y = event.offsetY;
    guessX = x;
    guessY = y;
    console.log("x coords: " + guessX + ", y coords: " + guessY);
}

<canvas id="puppyCanvas" width="500" height="500" style="border:2px solid black" onclick="storeGuess(event)"></canvas>

回答2:

I am using this piece of code.

var myCanvas = document.querySelector('#canvas');

myCanvas.addEventListener('click', function(event) {
    var rect = myCanvas.getBoundingClientRect();
    var x = event.clientX - rect.left;
    var y = event.clientY - rect.top;
    console.log("x: " + x + " y: " + y); 
}, false);

<canvas width="400" height="400" id="canvas" style="background-color: lightblue"></canvas>

来源：https://stackoverflow.com/questions/43172115/get-the-mouse-coordinates-when-clicking-on-canvas

标签

canvas

coordinates

mouse