js canvas realizes slider verification

<template>
 <div class="sliderContent">
 <div class="imgDev" :style="'width:' + width + 'px;'">
 <canvas :id="id" :width="width" :height="height"></canvas>
 <canvas
 class="slider"
 :id="id + 'sliderBlock'"
 :width="width"
 :height="height"
 :style="'left:' + sliderLeft + 'px;'"
 ></canvas>
 </div>
 <div class="moveSLider" :style="'width:' + width + 'px'">
 <div class="react" @mousedown.stop="moveBall($event)">
 <div
 class="yuan"
 :style="'left:' + (sliderLeft + 10) + 'px;'"
 ></div>
 </div>
 </div>
 </div>
</template>

<script>
export default {
 data() {
 return {
 width: 200, //Box width height: 200, //Box height. This parameter does not work when the original ratio of the image is set. id: new Date().getTime(),
 r: 9, //The radius of the semicircle w: 40, //The width of the slider imgOriginalScale: true, //Whether the image displays the original scale sliderLeft: 0, //The initial position of the slider rangeValue:4, //When the slider is in what range is it considered correct imgsrc:require("../assets/img/ver-2.png") //Introduce the background image you want };
 },
 mounted() {
 this.init();
 },
 methods: {
 init() {
 this.loadImage();
 },
 loadImage() {//Load image let mainDom = document.getElementById(this.id);
 let bg = mainDom.getContext("2d");
 let blockDom = document.getElementById(this.id + "sliderBlock");
 let block = blockDom.getContext("2d");
 let imgsrc = this.imgsrc;
 let img = document.createElement("img");
 img.style.objectFit = "scale-down";
 img.src = imgsrc;
 img.onload = () => {
 if (this.imgOriginalScale) {
 //Calculate the original proportion of the image based on the size change of the image mainDom.height = (img.height / img.width) * mainDom.width;
 blockDom.height = (img.height / img.width) * blockDom.width;
 }
 bg.drawImage(img, 0, 0, mainDom.width, mainDom.height);
 this.drawBlock(bg, mainDom.width, mainDom.height, "fill"); //Draw the slider part this.drawBlock(block, blockDom.width, blockDom.height, "clip", img); //Draw the slider part Note that you must clip first and then draw the image (the image must be passed in here or there is no way to control it)
 };
 },
 drawBlock(ctx, width, height, type, img) { //This is a two-in-one function that can draw the shadow part and cut out the puzzle shape let { w, r, sliderLeft } = this;
 //This place uses random numbers and the display position is different each time var x = this.random(30, width - w - r - 1); //Here the maximum value is to prevent the slider from being hidden, so the width of the slider should be subtracted. There is a semicircle, so the semicircle position should be subtracted var y = this.random(10, height - w - r - 1);
 if (type == "clip") {//Here we need to make sure that both objects are at the same y value x = sliderLeft;
 y = this.y;
 } else {
 this.x = x;
 this.y = y;
 }
 let PI = Math.PI;
 //Draw ctx.beginPath();
 //left
 ctx.moveTo(x, y);
 //top
 ctx.arc(x + (w + 5) / 2, y, r, -PI, 0, true);
 ctx.lineTo(x + w + 5, y);
 //right
 ctx.arc(x + w + 5, y + w / 2, r, 1.5 * PI, 0.5 * PI, false);
 ctx.lineTo(x + w + 5, y + w);
 //bottom
 ctx.arc(x + (w + 5) / 2, y + w, r, 0, PI, false);
 ctx.lineTo(x, y + w);
 ctx.arc(x, y + w / 2, r, 0.5 * PI, 1.5 * PI, true);
 ctx.lineTo(x, y);
 if (type == "clip") {
 ctx.shadowBlur = 10;
 ctx.shadowColor = "black";
 }
 ctx.lineWidth = 1;
 ctx.fillStyle = "rgba(0, 0, 0, 0.4)"; //Set the background color ctx.stroke();
 ctx[type]();
 if (img) {
 ctx.drawImage(img, -this.x, 0, width, height);
 }
 ctx.globalCompositeOperation = "xor";
 },
 random(min, max) {
 return parseInt(Math.floor(Math.random() * (max - min)) + min);
 },
 moveBall(e) {//When clicking the little red ball var oldx = e.pageX;
 document.onmousemove = (e) => {//Here you need to bind the document object, otherwise it will not move when you leave it var x = e.pageX;
 if(this.sliderLeft+x-oldx<=0){//Judge the left boundary here this.sliderLeft = 0;
 }else if(this.sliderLeft+x-oldx>=this.width-this.r*2-this.w){//Judge the right boundary here this.sliderLeft = this.width-this.r*2-this.w;
 }else{
 this.sliderLeft += x - oldx;
 }
 oldx = x;
 };
 this.laveBall();
 },
 laveBall() {//Clear state when mouse is released document.onmouseup = ()=> {
 document.onmousemove = null;
 if(this.sliderLeft<(this.x+this.rangeValue)&&this.sliderLeft>(this.x-this.rangeValue)){
 console.log("Congratulations, you succeeded")
 }else{//Reset the slider position when it is not selected this.sliderLeft = 0;
 }
 };
 },
 },
};
</script>
<style lang="scss" scoped>
.moveSLider {
 position: relative;
 margin: 0 auto;
 height: 50px;
 .react {
 .yuan
 position: absolute;
 left: 0;
 top: 50%;
 transform: translate(0, -50%);
 width: 30px;
 height: 30px;
 background-color: red;
 border-radius: 50%;
 cursor: pointer;
 }
 position: absolute;
 left: 0;
 top: 50%;
 transform: translate(0, -50%);
 width: 100%;
 height: 20px;
 background-color: rosybrown;
 }
}
.imgDev {
 position: relative;
 margin: 0 auto;
 .slider {
 position: absolute;
 left: 0;
 top: 0;
 background-color: transparent;
 }
}
</style>

drawBlock(ctx, width, height, type, img) { //This is a two-in-one function that can draw the shadow part and cut out the puzzle shape. let { w, r, sliderLeft } = this; //w is the width, r is the radius of the circle. sliderLeft is the initial position of the slider. //This place uses random numbers and the display position is different each time. var x = this.random(30, width - w - r - 1); //Here the maximum value is to prevent the slider from being hidden, so the width of the slider must be subtracted. There is a semicircle, so the semicircle position must be subtracted. var y = this.random(10, height - w - r - 1);
 if (type == "clip") {//Here we need to make sure that both objects are at the same y value x = sliderLeft;
 y = this.y;
 } else {
 this.x = x;
 this.y = y;
 }
 let PI = Math.PI;
 //Draw ctx.beginPath();
 //left
 ctx.moveTo(x, y);
 //top
 ctx.arc(x + (w + 5) / 2, y, r, -PI, 0, true);
 ctx.lineTo(x + w + 5, y);
 //right
 ctx.arc(x + w + 5, y + w / 2, r, 1.5 * PI, 0.5 * PI, false);
 ctx.lineTo(x + w + 5, y + w);
 //bottom
 ctx.arc(x + (w + 5) / 2, y + w, r, 0, PI, false);
 ctx.lineTo(x, y + w);
 ctx.arc(x, y + w / 2, r, 0.5 * PI, 1.5 * PI, true);
 ctx.lineTo(x, y);
 if (type == "clip") {
 ctx.shadowBlur = 10;
 ctx.shadowColor = "black";
 }
 ctx.lineWidth = 1;
 ctx.fillStyle = "rgba(0, 0, 0, 0.4)"; //Set the background color ctx.stroke();
 ctx[type]();
 if (img) {//Why do we need to load the image here? Because the height is dynamic and must be calculated before it is put in.//Another reason is that you need to crop the image before loading it. ctx.drawImage(img, -this.x, 0, width, height);
 }
},