Question

我想在画布上绘制图像，但是当我点击画布时，图像只会出现在该位置。我还学习了element.getBoundingClientRect方法，它可以让我获得画布的偏移量。我想组合它们，所以当点击画布的任何部分时，图像将出现在同一位置，X和Y偏移也将显示出来。

目前我的图像将显示onload，当我在画布上点击图像将出现在同一位置时，如何更改它。第二件事是，同时显示图像的X和Y偏移位置。

Answer 1

像这样修改你的JS代码：

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");

$results=$("#results");
$dotposition=$("#dotposition");
var position = {x: 0, y: 0};

function handleMouseMove(e) {
    e.preventDefault();
    e.stopPropagation();

    // You could calc the offsets once if you know
    // the user will not scroll the canvas
    var BB=canvas.getBoundingClientRect();
    var offsetX=BB.left;
    var offsetY=BB.top;

    mouseX=parseInt(e.clientX-offsetX);
    mouseY=parseInt(e.clientY-offsetY);
    $results.text("Mouse position: "+mouseX+" / "+mouseY);
    position.x = mouseX;
    position.y = mouseY;
}

function handleMouseClick(e) {
    //Clearing the canvas before redraw, remove this line if you want to keep prev images
    ctx.clearRect ( 0 , 0 , canvas.width , canvas.height );

    ctx.drawImage(img,position.x - img.width / 2,position.y - img.height / 2);
    $dotposition.text("Dot position: "+position.x+" / "+position.y);
}

var img = new Image();
img.onload = function(){
    canvas.onmousemove = handleMouseMove;
    canvas.onclick = handleMouseClick;
};
img.src="https://dl.dropboxusercontent.com/s/7vlxwy1156wnhcw/redFood.png";

http://jsfiddle.net/ZH4KW/1/

在HTML5画布上绘制图像

1 个答案: