javascript - 隐藏页面顶部的空白区域

Question

如果您点击“运行代码片段”或者如果您选中 here ，开始时您会看到很多空白区域，向下滚动后我们只能看到图像。

我想隐藏顶部的那些空白区域。

我试过 position:relative;顶部:一些像素；底部:一些 px； 但它对我没有用。

var canvas = new fabric.Canvas('canvas');
document.getElementById('file').addEventListener("change", function (e) {
  var file = e.target.files[0];
  var reader = new FileReader();
  reader.onload = function (f) {
    var data = f.target.result;                    
    fabric.Image.fromURL(data, function (img) {
     // var oImg = img.set({left: 0, top: 0, angle: 00,width:100, height:100}).scale(0.9);
	  var oImg = img.set({left: 0, top: 0, angle: 00, width: canvas.getWidth(), height: canvas.getHeight()});
      canvas.add(oImg).renderAll();
      var a = canvas.setActiveObject(oImg);
      var dataURL = canvas.toDataURL({format: 'png', quality: 0.8});
    });
  };
  reader.readAsDataURL(file);
});


var img = new Image();
img.onload = function() {
  //draw after loading
  var canvas = document.getElementById('case_canvas');
  var ctx = canvas.getContext("2d");
  ctx.drawImage(img, 0, 0, img.naturalWidth, img.naturalHeight);
}

img.src = "http://i.stack.imgur.com/xgNw7.png";
//^^ this will start loading the image

/*.canvas-container {
  background: url("http://i.stack.imgur.com/xgNw7.png") no-repeat fixed center;

  }
  */
 
 .canvas-container {
 width: 300px; height: 500px;  position: relative; -webkit-user-select: none; top:900px;
 }
 
 #canvas
 {
  border: 1px solid black;
  top:500px;
}

#file
{
	position:relative;top:900px;
}

.lower-canvas

{
	position: absolute; width: 300px; height: 500px; bottom:400px; left: 0px; -webkit-user-select: none;
}

.upper-canvas {
position: absolute; width: 300px; height: 500px; left: 0px; top: 0px; -webkit-user-select: none; cursor: default;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://rawgit.com/kangax/fabric.js/master/dist/fabric.min.js"></script>
<input  type="file" id="file"><br />
<canvas id="canvas" width="450" height="450"></canvas>	

<div class="canvas-container">
<canvas id="case_canvas" width="300" height="500" class="lower-canvas" ></canvas>
<canvas class="upper-canvas " width="300" height="500" ></canvas>
</div>

Answer 1

您必须将 Canvas 容器的顶部位置从 900 更改为较低的值。

查看下面的片段

var canvas = new fabric.Canvas('canvas');
document.getElementById('file').addEventListener("change", function (e) {
  var file = e.target.files[0];
  var reader = new FileReader();
  reader.onload = function (f) {
    var data = f.target.result;                    
    fabric.Image.fromURL(data, function (img) {
     // var oImg = img.set({left: 0, top: 0, angle: 00,width:100, height:100}).scale(0.9);
	  var oImg = img.set({left: 0, top: 0, angle: 00, width: canvas.getWidth(), height: canvas.getHeight()});
      canvas.add(oImg).renderAll();
      var a = canvas.setActiveObject(oImg);
      var dataURL = canvas.toDataURL({format: 'png', quality: 0.8});
    });
  };
  reader.readAsDataURL(file);
});


var img = new Image();
img.onload = function() {
  //draw after loading
  var canvas = document.getElementById('case_canvas');
  var ctx = canvas.getContext("2d");
  ctx.drawImage(img, 0, 0, img.naturalWidth, img.naturalHeight);
}

img.src = "http://i.stack.imgur.com/xgNw7.png";
//^^ this will start loading the image

/*.canvas-container {
  background: url("http://i.stack.imgur.com/xgNw7.png") no-repeat fixed center;

  }
  */
 
 .canvas-container {
 width: 300px; height: 500px;  position: relative; -webkit-user-select: none; top:0px;
 }
 
 #canvas
 {
  border: 1px solid black;
  top:500px;
}

#file
{
	position:relative;top:0px;
}

.lower-canvas

{
	position: absolute; width: 300px; height: 500px; bottom:400px; left: 0px; -webkit-user-select: none;
}

.upper-canvas {
position: absolute; width: 300px; height: 500px; left: 0px; top: 0px; -webkit-user-select: none; cursor: default;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://rawgit.com/kangax/fabric.js/master/dist/fabric.min.js"></script>
<input  type="file" id="file"><br />
<canvas id="canvas" width="450" height="450"></canvas>	

<div class="canvas-container">
<canvas id="case_canvas" width="300" height="500" class="lower-canvas" ></canvas>
<canvas class="upper-canvas " width="300" height="500" ></canvas>
</div>