How to set brush thickness in javascript

With the development of Web technology, more and more front-end developers have begun to pay attention to user experience, among which the drawing function is becoming more and more widely used. Implementing the drawing function on the Web is inseparable from the drawing API provided by the browser, of which setting the brush thickness is one of the basic functions. This article will introduce how to use JavaScript to set the brush thickness.

1. What is brush thickness?

Brush thickness refers to the line width of the brush when drawing, also called line width. Adjusting the thickness of the brush can change the visual effect of the drawn graphics, making the drawn graphics more beautiful and realistic. At the same time, setting the brush thickness is also a basic skill in Web drawing.

2. How to set the brush thickness?

Setting the brush thickness in JavaScript can be achieved using the lineWidth attribute in the canvas object. The code is as follows:

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

context.lineWidth = 5; //设置画笔粗细为5像素

In the above code, we first obtain the canvas element through the getElementById method and use getContext Method to obtain the 2D drawing context. Then, use the lineWidth property to set the brush thickness. The value of this property is the width of the line. Here, we set the brush weight to 5 pixels.

It should be noted that when setting the brush thickness, different browsers may have different implementation methods, so compatibility needs to be processed when using it.

The following is a compatibility processing code for setting the brush thickness in different browsers:

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

//获取浏览器厂商前缀
var vendorPrefix = (function() {
    var styles = window.getComputedStyle(document.documentElement, ''),
        pre = (Array.prototype.slice.call(styles).join('').match(/-(moz|webkit|ms)-/) || (styles.OLink === '' && ['', 'o']))[1];
    return '-' + pre + '-';
})();

context.lineWidth = 5;

//兼容性处理，针对不同浏览器设置不同的前缀
context.lineWidth = vendorPrefix + 'line-width: 5px';

In the above code, we obtain the prefix of the browser manufacturer and use This prefix is ​​used to set the brush thickness for cross-browser compatibility.

3. Example demonstration

In order to better understand how to set the brush thickness, we can use the following example to demonstrate.

First, create a canvas element and two buttons in HTML, the code is as follows:

<canvas id="canvas" width="400" height="400"></canvas>
<button id="btn1">线条变细</button>
<button id="btn2">线条变粗</button>

Then, bind the event handler of the button in JavaScript, the code is as follows:

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

var lineWidth = 5; //初始画笔粗细为5像素

//绑定按钮事件处理程序
document.getElementById("btn1").onclick = function() {
    if(lineWidth > 1) {
        lineWidth -= 1; //每次减少1像素
        context.lineWidth = lineWidth;
    }
};
document.getElementById("btn2").onclick = function() {
    lineWidth += 1; //每次增加1像素
    context.lineWidth = lineWidth;
};

In the above code, we first define a variable lineWidth with an initial brush thickness of 5 pixels, and change the value of the variable in the button event handler by increasing or decreasing each time to achieve the effect of dynamically changing the brush thickness.

Finally, set the style of the canvas element in CSS. The code is as follows:

canvas {
    border: 1px solid #ccc;
}

Now, we can change the brush thickness by clicking the button and preview its effect in real time. For specific demonstrations, please refer to the following examples:

The lines become thicker

<script><br>var canvas = document.getElementById( "canvas");<br>var context = canvas.getContext("2d");</p> <p>var lineWidth = 5; //The initial brush thickness is 5 pixels</p> <p>//Bind button Event handler<br>document.getElementById("btn1").onclick = function() {</p> <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">if(lineWidth &gt; 1) {     lineWidth -= 1; //每次减少1像素     context.lineWidth = lineWidth; }</pre><div class="contentsignin">Copy after login</div></div> <p>};<br>document.getElementById("btn2").onclick = function() {</p> <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">lineWidth += 1; //每次增加1像素 context.lineWidth = lineWidth;</pre><div class="contentsignin">Copy after login</div></div> <p>};<br></script>

IV. Summary

In Web drawing, setting the brush thickness is a basic function and an important means to improve user experience. Through the lineWidth property in the canvas object, we can easily set the line width of the brush to achieve different drawing effects. I hope this article can give readers a better understanding of how to set the brush thickness and better apply it to web drawing in actual development.

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