css3 implements drawing pictures onto canvas (code example)

This article will introduce you to the method of drawing pictures on the canvas, which is suitable for use on PC and mobile terminals. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Draw a picture on the canvas

<canvas id="myCanvas" width="1000px" height="200px" >您的浏览器不支持canvas标签。</canvas>

var canvas = document.getElementById("myCanvas");
//获取画笔
var ctx=canvas.getContext('2d');
//声明Image对象
var img=new Image();
//获取img路径
img.src="img/num.png";
//把图片画到画布上
img.onload=function(){
	ctx.drawImage(img,57,0,57,64);
}

If you want to put several different pictures on the canvas, if there are several pictures, you need to declare the object several times and obtain the path several times. Paint on the canvas several times.

The following are 6 pictures I drew on the canvas,

var canvas = document.getElementById("myCanvas");
//获取画笔
			var ctx=canvas.getContext('2d');
			//声明Image对象
			var img=new Image();
			var img1=new Image();
			var img2=new Image();
			var img3=new Image();
			var img4=new Image();
			var img5=new Image();
			//获取img路径
			img.src="img/num.png";
			img1.src="img/num/1.png"
			img2.src="img/num/4.png"
			img3.src="img/num/2.png"
			img4.src="img/num/5.png"
			img5.src="img/num/7.png"
			//把图片画到画布上
			img.onload=function(){
				ctx.drawImage(img,57,0,57,64);
			}
			img1.onload=function(){
				ctx.drawImage(img1,114,0,57,64);
			}
			img2.onload=function(){
				ctx.drawImage(img2,171,0,57,64);
			}
			img3.onload=function(){
				ctx.drawImage(img3,228,0,57,64);
			}
			img4.onload=function(){
				ctx.drawImage(img4,285,0,57,64);
			}
			img5.onload=function(){
				ctx.drawImage(img5,342,0,57,64);
			}

ctx.drawImage（img5,342,0,57,64）里面的参数分别为，图片，x坐标，y坐标，图片宽度，图片高度

Rendering:

Now, I want to make the canvas The pictures I draw can be adapted to both PC and mobile terminals. Then, I have to reprocess these codes. Now I only need to change the code to draw the pictures on the canvas.

 //把图片画到画布上
        function getCurrentImg() {
            var docW = $(document.body).width(); //获取页面宽度
              if (docW == 640) {//640是PC端的宽度
                 img.onload = function () {
                    ctx.drawImage(img, 22, 58, 55, 66);
                }
                img1.onload = function () {
                    ctx.drawImage(img1, 77, 58, 55, 66);
                }
                img2.onload = function () {
                    ctx.drawImage(img2, 132, 58, 55, 66);
                }
                img3.onload = function () {
                    ctx.drawImage(img3, 187, 58, 55, 66);
                }
                img4.onload = function () {
                    ctx.drawImage(img4, 242, 58, 55, 66);
                }
                img5.onload = function () {
                    ctx.drawImage(img5, 297, 58, 55, 66);
                }
              } else if (docW < 640) {//移动端的时候
                     img.onload = function () {
                        ctx.drawImage(img, 19, 51, 40, 45);
                    }
                    img1.onload = function () {
                        ctx.drawImage(img1, 59, 51, 40, 45);
                    }
                    img2.onload = function () {
                        ctx.drawImage(img2, 99, 51, 40, 45);
                    }
                    img3.onload = function () {
                        ctx.drawImage(img3, 139, 51, 40, 45);
                    }
                    img4.onload = function () {
                        ctx.drawImage(img4, 179, 51, 40, 45);
                    }
                    img5.onload = function () {
                        ctx.drawImage(img5, 219, 51, 40, 45);
                    }
              }
        }
        getCurrentImg();
        $(window).resize(function () {//页面大小发生改变的时候自动刷新页面
            var docW = $(document.body).width();
            var canvas = document.getElementById("myCanvas");
             //var ctx = canvas.getContext(&#39;2d&#39;);
             if (docW == 640) {
                canvas.height=canvas.height;//页面改变时清除画布
                 ctx.drawImage(img, 22, 58, 55, 66);
                    ctx.drawImage(img1, 77, 58, 55, 66);
                    ctx.drawImage(img2, 132, 58, 55, 66);
                    ctx.drawImage(img3, 187, 58, 55, 66);
                    ctx.drawImage(img4, 242, 58, 55, 66);
                    ctx.drawImage(img5, 297, 58, 55, 66);
                      
             } else if (docW < 640) {
                 canvas.height=canvas.height;//页面改变时清除画布
                    ctx.drawImage(img, 19, 51, 40, 45);
                   ctx.drawImage(img1, 59, 51, 40, 45);
                    ctx.drawImage(img2, 99, 51, 40, 45);
                    ctx.drawImage(img3, 139, 51, 40, 45);
                    ctx.drawImage(img4, 179, 51, 40, 45);
                    ctx.drawImage(img5, 219, 51, 40, 45);
                      
            }
        })

The resize() method is certain I only found out about it after some exploration. If not, you have to manually refresh the page every time you switch between PC and mobile. Although the function can still be implemented, the user experience is not very good.

Be sure to note that when the page size changes, you must clear the canvas first, otherwise there will be canvas overlays of different page sizes

I just briefly distinguish between the mobile terminal and the PC terminal. If If it is adaptive on mobile devices with different screen sizes, more if(){}else{} judgments are needed.

Summary: The above is the entire content of this article, I hope it will be helpful to everyone's study. For more related tutorials, please visit CSS3 Video Tutorial, Html5 Video Tutorial!

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