canvas scrolls too far

问题:

I'm using this answer https://stackoverflow.com/a/36233727/1350146 to scroll a canvas in a div. I'm also hiding the scrollbar. The problem is it appears to scroll too far, in this case if you scroll down you can see the red of the div the canvas is in.

I've tried messing with padding & margins and different sizes but no luck.

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = '#00aa00'
ctx.fillRect(0, 0, c.width, c.height);
ctx.fillStyle = '#fff'
ctx.font='12pt A'
ctx.fillText("scroll here to see red from screen div", 30, 50);

.screen {
  background: red;
  height: 100px;
  width: 300px;
  overflow: auto;
  border-radius: 20px;
  
}

::-webkit-scrollbar {
  width: 0px;
  height: 0px;
}

<div class="screen">
  <canvas id="myCanvas" width="300" height="120">
  </canvas>
</div>

How can I make it scroll just to the end of the canvas and not show any of the container div underneath?

Thanks!

回答1:

Make the canvas a block element. By default, canvas is an inline element and it will behave similary to an img; thus you will have the whitespace issue due to vertical alignement (Image inside div has extra space below the image)

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = '#00aa00'
ctx.fillRect(0, 0, c.width, c.height);
ctx.fillStyle = '#fff'
ctx.font='12pt A'
ctx.fillText("scroll here to see red from screen div", 30, 50);

.screen {
  background: red;
  height: 100px;
  width: 300px;
  overflow: auto;
  border-radius: 20px;
}
canvas {
 display:block;
}

::-webkit-scrollbar {
  width: 0px;
  height: 0px;
}

<div class="screen">
  <canvas id="myCanvas" width="300" height="120">
  </canvas>
</div>

回答2:

Use a negative margin-bottom value for your canvas element. Anything between margin-bottom: -5px; and margin-bottom: -105px; will work for this example.

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = '#00aa00'
ctx.fillRect(0, 0, c.width, c.height);
ctx.fillStyle = '#fff'
ctx.font='12pt A'
ctx.fillText("scroll here to see red from screen div", 30, 50);

.screen {
  background: red;
  height: 100px;
  width: 300px;
  overflow: auto;
  border-radius: 20px;
  
}

::-webkit-scrollbar {
  width: 0px;
  height: 0px;
}

canvas {
  margin-bottom: -5px;
}

<div class="screen">
  <canvas id="myCanvas" width="300" height="120">
  </canvas>
</div>