[英]Identify which object on screen clicked in html5 canvas javascript?
[英]How to identify which canvas was clicked
在下面的代碼中,單擊兩個畫布,將打開文件瀏覽器以打開圖像。 我想在單擊的畫布上顯示打開的圖像。 但
1)問題是一旦控件位於handleFile中,我不知道最初單擊了哪個畫布! 我該怎么做或如何將canvas作為參數傳遞給handleFile函數?
2)如果我想在canvas1上單擊時要在textarea1上寫一些東西,而在canvas2上單擊時要寫在textarea2上怎么辦?
<html>
<head>
</head>
<body>
<input type="file" id="fileLoader" name="fileLoader" style="display: none" />
<canvas id="bufferCanvas"></canvas>
<canvas id="canvas1" width="200" height="200" style="cursor:pointer; border:2px solid #000000"></canvas>
<canvas id="canvas2" width="200" height="200" style="cursor:pointer; border:2px solid #ff6a00"></canvas>
<textarea id="textarea1" rows="4" cols="50"></textarea>
<textarea id="textarea2" rows="4" cols="50"></textarea>
<script src="upload.js"></script>
</body>
</html>
這是upload.js
var fileLoader = document.getElementById('fileLoader');
var bufferCanvas = document.getElementById('bufferCanvas');
var allCanvases = document.getElementsByTagName("Canvas");
for (var i = 1; i < allCanvases.length; ++i) {
allCanvases[i].getContext("2d").fillStyle = "blue";
allCanvases[i].getContext("2d").font = "bold 20px Arial";
allCanvases[i].getContext("2d").fillText("image " + i + " of 1", 22, 20);
allCanvases[i].onclick = function (e) {
fileLoader.click(e);
}
}
fileLoader.addEventListener('change', handleFile, false);
var textarea1 = document.getElementById('textarea1');
var ctx = bufferCanvas.getContext('2d');
function handleFile(e) {
// I wanna know what canvas was clicked
//So I can display the image on the canvas which was clicked
var reader = new FileReader();
reader.onload = function (event) {
var img = new Image();
img.onload = function () {
bufferCanvas.width = img.width;
bufferCanvas.height = img.height;
ctx.drawImage(img, 0, 0);
dataURL = bufferCanvas.toDataURL('image/png'); // here is the most important part because if you dont replace you will get a DOM 18 exception;
// window.location.href = dataURL;// opens it in current windows for testing
textarea1.innerHTML = dataURL;
}
img.src = event.target.result;
}
reader.readAsDataURL(e.target.files[0]);
}
問題是畫布的onclick
觸發了具有自己事件的文件fileloader
的單擊。 要執行您想要的操作,可以創建全局變量來保存被單擊的<canvas>
。
var fileLoader = document.getElementById('fileLoader');
var bufferCanvas = document.getElementById('bufferCanvas');
var allCanvases = document.getElementsByTagName("Canvas");
var clickedCanvas = ''; //<---- will hold the triggering canvas
然后在您的onclick
函數中,您可以將html element
設置為clickedCanvas
for (var i = 1; i < allCanvases.length; ++i) {
...
...
...
allCanvases[i].onclick = function (e) {
clickedCanvas = e.srcElement; // <--- set the clicked on canvas
fileLoader.click(e);
}
}
現在在function handleFile(e)
您應該能夠從clickedCanvas
獲取畫布
同樣,在完成后,我也會清除clickedCanvas
,以免保留最后一個事件。
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