如何在画布之后与HTML交互？ [英] How to interact with HTML behind a canvas?

问题描述

场景：
我有一个网站，目前在本地托管，我希望能够在网站顶部的画布上绘画，如下所示。然而，我不仅希望允许用户在网站上绘画，而且随后在用户与该页面的其余部分交互的同时使该图形保持在该特定的网页上。例如。填写表单或与下拉菜单互动等。
注意： HTML Canvas覆盖整个页面（而不仅仅是视口）。此外，还有一个按钮可用于区分绘图和与HTML互动

< img src =https://i.stack.imgur.com/c9cBK.pngalt =输入图片说明>

具体问题：
在画布出现时，如何与网页上的普通HTML元素进行互动。我知道画布会从一个页面重置到页面，这很好 - 我不是想解决这个问题。我只想解决一个页面。

尝试的方法
我试过播放透明度，zIndex和其他CSS属性。

替代解决方案
1.我知道这可以使用SVG解决，并且只需在整个网页上以透明的DIV覆盖。但是我不想使用这种方法，如果可能，坚持使用画布找到一个解决方案。


2.目前HTML Canvas覆盖整个页面（不仅仅是视口），所以我想我可以有一个动态调整大小的画布取决于在页面上绘制多少。但是，我可能只是使用SVG的。

想法？

The Scenario:
I have a website, currently hosted locally and I want to be able to draw on a canvas over the top of the website, as illustrated below. However, not only do I want to allow a user to draw on the website but also then have the drawing remain on the that specific webpage whilst the user interacts with the rest of that page. E.g. filling out forms or interacting with drop downs, etc.
NB: The HTML Canvas covers the entire page (not just the viewport). Additionally, there would be a button to distinguish between drawing and interacting with HTML



The specific problem:
How to interact with normal HTML elements on a web page whilst a canvas is present. I know the canvas will reset from page to page, and that is fine - I'm not trying to solve that. I'm only trying to solve for a single page.

Methods tried
I've tried playing with transparency, zIndex and other css properties.

Alternative solutions
1. I know that this can be solved using SVG's and just overlaying them in a transparent DIV over the whole webpage. But I'd prefer not to use this method and stick with finding a solution using canvas if possible.

2. Currently the HTML Canvas covers the entire page (not just the viewport) so I suppose I could have a dynamically resizing canvas dependent on how much was draw on the page. However, then I might as well just use SVG's.

Thoughts? I'm open to libs/snippets, anything.

推荐答案

解决方法之一是：

• 使用CSS将默认点事件设置为none


• 为要用于点击的元素启用指针事件，捕获器（背景，正文或元素）


• 根据设计需要使用正文或元素作为事件捕获器，用于上面未使用的事件。


• 将指针事件设置为none的所有点击都放在画布上。

• Set default point-events to none using CSS
• Enable pointer events for elements you want to use for clicks etc. including event catcher (background, body or an element)
• Use body or an element depending on what your design requires, as event-catcher for events that aren't consumed above.
• Put canvas on top of everything with pointer-events set to none

可点击元素（或要用于事件的元素）现在将在后面结束。

Any click that isn't consumed by a clickable element (or an element you want to use for events) will now end at the back. Simply transfer the coordinates from this backing element to canvas to draw.

演示不是完美的即不考虑本地触摸事件/手势，它绘制点而不是线等），但它应该足以显示基本原则，让你去。

Demo isn't flawless (ie. doesn't consider things like native touch events/gestures, it draws dots not lines etc.) but it should be enough to show the basic principle and get you going.

我们在这里使用body来捕获任何未被消耗的事件。向下滚动以绘制并点击文本中的第二个链接。

We simply use body here to catch any events that wasn't consumed. Scroll down to draw and to click the second link in the text.

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

setup();
window.onresize = setup;
window.onmousedown = function(e) {
  isDown = true;
  draw(e);
};
window.onmousemove = function(e) {if (isDown) draw(e);};
window.onmouseup = function() {isDown = false};

function setup() {
  canvas.width = window.innerWidth;
  canvas.height = parseInt(getComputedStyle(document.body).getPropertyValue("height"), 10);
  ctx.fillStyle = "rgba(0,160,255,0.4)";
}

function draw(e) {
  var rect = canvas.getBoundingClientRect();
  ctx.beginPath();
  ctx.arc(e.clientX - rect.left, e.clientY - rect.top, 15, 0, 6.28);
  ctx.fill();
}

* { /* optimize by being more specific, here just for demo */
  pointer-events:none;
  }
a {
  color:#00c;
  pointer-events:auto;
  cursor:pointer;
  text-decoration:underline;
  }
html, body {
  height:3500px;
  width:100%;
  }
body {
  pointer-events:auto;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  }
#poster {
  width:80%;
  margin:50px auto 0 auto;
  background:rgba(0,0,0,0.2);
  padding:20px;
  box-sizing:border-box;
  z-index:1;
  }
#canvas {
  position:absolute;
  left:0;
  top:0;
  z-index:1000;
  }

<h1>Demonstration</h1>

<div id="poster">
  <h2>Drawable page</h2>
  <a onclick="alert('Was clicked');return false">Click me</a>
</div>

<h3>The standard Lorem Ipsum passage, used since the 1500s</h3><p>"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."</p><h3>Section 1.10.32 of "de Finibus Bonorum et Malorum", written by Cicero in 45 BC</h3><p>"Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem. Ut enim ad minima veniam, quis nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut aliquid ex ea commodi consequatur? Quis autem vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil molestiae consequatur, vel illum qui dolorem eum fugiat quo voluptas nulla pariatur?"</p>
<h3>1914 translation by H. Rackham</h3>
<p>"But I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system, and expound the actual teachings of the great explorer of the truth, the master-builder of human happiness. No one rejects, dislikes, or avoids pleasure itself, because it is pleasure, but because those who do not know how to pursue pleasure rationally encounter consequences that are extremely painful. Nor again is there anyone <b><a onclick="alert('yeehaw');return false">who loves</a></b> or pursues or desires to obtain pain of itself, because it is pain, but because occasionally circumstances occur in which toil and pain can procure him some great pleasure. To take a trivial example, which of us ever undertakes laborious physical exercise, except to obtain some advantage from it? But who has any right to find fault with a man who chooses to enjoy a pleasure that has no annoying consequences, or one who avoids a pain that produces no resultant pleasure?"</p>
<h3>Section 1.10.33 of "de Finibus Bonorum et Malorum", written by Cicero in 45 BC</h3>
<p>"At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga. Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus. Temporibus autem quibusdam et aut officiis debitis aut rerum necessitatibus saepe eveniet ut et voluptates repudiandae sint et molestiae non recusandae. Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat."</p>
<h3>1914 translation by H. Rackham</h3>
<p>"On the other hand, we denounce with righteous indignation and dislike men who are so beguiled and demoralized by the charms of pleasure of the moment, so blinded by desire, that they cannot foresee the pain and trouble that are bound to ensue; and equal blame belongs to those who fail in their duty through weakness of will, which is the same as saying through shrinking from toil and pain. These cases are perfectly simple and easy to distinguish. In a free hour, when our power of choice is untrammelled and when nothing prevents our being able to do what we like best, every pleasure is to be welcomed and every pain avoided. But in certain circumstances and owing to the claims of duty or the obligations of business it will frequently occur that pleasures have to be repudiated and annoyances accepted. The wise man therefore always holds in these matters to this principle of selection: he rejects pleasures to secure other greater pleasures, or else he endures pains to avoid worse pains."</p>

<canvas id="canvas"></canvas>

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