Web Front-end
H5 Tutorial
Mobile Touch event and H5-Canvas pixel detection to realize scratch-off
Mobile Touch event and H5-Canvas pixel detection to realize scratch-off
Recently I have been flooded with Alipay’s Jifu character
I still haven’t seen Jingyefuค(TㅅT) and I’m heartbroken
I’ll bring it to you today The
effect of the scratch card on the mobile terminal is like this
Swipe your hand to trigger the scratch card
When the scratch card area reaches more than 70%, all gray layers will be automatically scratched 
Not a lot of code
That’s all the code
<!DOCTYPE html><html lang="en"><head>
<meta charset="UTF-8">
<meta content="width=device-width,maximum-scale=1.0,minimum-scale=1.0,initial-scale=1.0,user-scalable=no" name="viewport">
<title>Scrape</title>
<style>
#myCanvas {
background-repeat: no-repeat;
background-position: center;
background-size: 200px 200px;
}
</style></head><body>
<canvas id="myCanvas" width=300 height=300></canvas>
<script>
var canvas = document.getElementById('myCanvas'),
ctx = canvas.getContext('2d'),
w = canvas.width;
h = canvas.height;
area = w * h;
l = canvas.offsetLeft;
t = canvas.offsetTop,
img = new Image();
var randomImg = function(){
var random = Math.random();
if(random < 0.4){
img.src = './1.png';
}else if(random > 0.6){
img.src = './2.png';
}else{
img.src = './award.jpg';
}
}; var bindEvent = function(){
canvas.addEventListener('touchmove', moveFunc, false);
canvas.addEventListener('touchend', endFunc, false);
}; var moveFunc = function(e){
var touch = e.touches[0],
posX = touch.clientX - l,
posY = touch.clientY - t;
ctx.beginPath();
ctx.arc(posX, posY, 15, 0, Math.PI * 2, 0);
ctx.fill();
}; var endFunc = function(e){
var data = ctx.getImageData(0, 0, w, h).data,
scrapeNum = 0;
for(var i = 3, len = data.length; i < len; i += 4){
if(data[i] === 0){
scrapeNum++;
}
} if(scrapeNum > area * 0.7){
ctx.clearRect(0, 0, w, h);
canvas.removeEventListener('touchmove', moveFunc, false);
canvas.removeEventListener('touchend', endFunc, false);
}
} var init = (function(){
ctx.fillStyle = "#ccc";
ctx.fillRect(0, 0, w, h);
randomImg();
img.addEventListener('load', function(){
canvas.style.backgroundImage = 'url(' + img.src +')';
ctx.globalCompositeOperation = 'destination-out';
bindEvent();
});
})(); </script></body></html>Let me explain it briefly
First of all, in the page we only We need a canvas element
<canvas id="myCanvas" width=300 height=300></canvas>
In CSS we need to set the style of the canvas background image in advance
#myCanvas {
background-repeat: no-repeat;
background-position: center;
background-size: 200px 200px;}In the script we first need to declare the required variables
var canvas = document.getElementById('myCanvas'),
ctx = canvas.getContext('2d'),
w = canvas.width;
h = canvas.height;
area = w * h;
l = canvas.offsetLeft;
t = canvas.offsetTop,
img = new Image();Get the canvas object and its context object
area variable is prepared for the following pixel detection
img is used for image preloading
The most critical function is the init initialization function
var init = (function(){
ctx.fillStyle = "#ccc";
ctx.fillRect(0, 0, w, h);
randomImg();
img.addEventListener('load', function(){
canvas.style.backgroundImage = 'url(' + img.src +')';
ctx.globalCompositeOperation = 'destination-out';
bindEvent();
});
})();The process is as follows:
Cover the entire canvas with the gray layer
Random pictures
Picture preloading
After loading, set the picture as canvas background
Before scratching the card, set
ctx .globalCompositeOperation = 'destination-out';#Bind listening events for canvas, Tuca
This globalCompositeOperation is the scratch-off The key
For the usage of this attribute, you can click here
var randomImg = function(){
var random = Math.random(); if(random < 0.4){
img.src = './1.png';
}else if(random > 0.6){
img.src = './2.png';
}else{
img.src = './award.jpg';
}
};The function of the randomImg function is to randomize pictures
For random pictures, you need to use Math.random() random numbers
canvas we need to bind two functions
touchmove and touchend
var moveFunc = function(e){
var touch = e.touches[0],
posX = touch.clientX - l,
posY = touch.clientY - t;
ctx.beginPath();
ctx.arc(posX, posY, 15, 0, Math.PI * 2, 0);
ctx.fill();};To draw a circle when sliding the screen
Because destination-out is set, a scratch effect occurs
Also note that every time it is triggered All mustctx.beginPath();
Otherwisectx.fill();will connect the previously drawn circles and scrape over a large area
var endFunc = function(e){
var data = ctx.getImageData(0, 0, w, h).data,
scrapeNum = 0;
for(var i = 3, len = data.length; i < len; i += 4){
if(data[i] === 0){
scrapeNum++;
}
} if(scrapeNum > area * 0.7){
ctx.clearRect(0, 0, w, h);
canvas.removeEventListener('touchmove', moveFunc, false);
canvas.removeEventListener('touchend', endFunc, false);
}
} When lifted, touchend will be triggered
In this function, we used ctx.getImageData() to obtain the pixel information of the canvas
For the usage of this function, you can click here
When the gray layer is scratched, the background of the canvas is behind it
So we can judge whether the layer has been scratched by judging whether A in the pixel information RGBA is 0
scrapeNum represents the scraped pixel Click
So by scrapeNum > area * 0.7
When the scraped range is greater than 70% of the total range
Clear the entire gray layer
and above It is the content of mobile touch event and H5-Canvas pixel detection to realize scratch-off. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
AI Hentai Generator
Generate AI Hentai for free.
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1386
52
Which schools use canvas?
Aug 18, 2023 pm 05:59 PM
Schools using canvas include Stanford University, MIT, Columbia University, University of California, Berkeley, etc. Detailed introduction: 1. Stanford University uses Canvas as its main online learning platform. Teachers and students at Stanford University use Canvas to manage and communicate course content, and learn through functions such as online discussions, assignment submissions, and exams; 2. Ma Provincial Polytechnic Institute and MIT also use Canvas as their online learning management system and conduct course management through the Canvas platform; 3. Columbia University, etc.
What are the canvas arrow plug-ins?
Aug 21, 2023 pm 02:14 PM
The canvas arrow plug-ins include: 1. Fabric.js, which has a simple and easy-to-use API and can create custom arrow effects; 2. Konva.js, which provides the function of drawing arrows and can create various arrow styles; 3. Pixi.js , which provides rich graphics processing functions and can achieve various arrow effects; 4. Two.js, which can easily create and control arrow styles and animations; 5. Arrow.js, which can create various arrow effects; 6. Rough .js, you can create hand-drawn arrows, etc.
What are the details of the canvas clock?
Aug 21, 2023 pm 05:07 PM
The details of the canvas clock include clock appearance, tick marks, digital clock, hour, minute and second hands, center point, animation effects, other styles, etc. Detailed introduction: 1. Clock appearance, you can use Canvas to draw a circular dial as the appearance of the clock, and you can set the size, color, border and other styles of the dial; 2. Scale lines, draw scale lines on the dial to represent hours or minutes. Position; 3. Digital clock, you can draw a digital clock on the dial to indicate the current hour and minute; 4. Hour hand, minute hand, second hand, etc.
What versions of html2canvas are there?
Aug 22, 2023 pm 05:58 PM
The versions of html2canvas include html2canvas v0.x, html2canvas v1.x, etc. Detailed introduction: 1. html2canvas v0.x, which is an early version of html2canvas. The latest stable version is v0.5.0-alpha1. It is a mature version that has been widely used and verified in many projects; 2. html2canvas v1.x, this is a new version of html2canvas.
Learn the canvas framework and explain the commonly used canvas framework in detail
Jan 17, 2024 am 11:03 AM
Explore the Canvas framework: To understand what are the commonly used Canvas frameworks, specific code examples are required. Introduction: Canvas is a drawing API provided in HTML5, through which we can achieve rich graphics and animation effects. In order to improve the efficiency and convenience of drawing, many developers have developed different Canvas frameworks. This article will introduce some commonly used Canvas frameworks and provide specific code examples to help readers gain a deeper understanding of how to use these frameworks. 1. EaselJS framework Ea
uniapp implements how to use canvas to draw charts and animation effects
Oct 18, 2023 am 10:42 AM
How to use canvas to draw charts and animation effects in uniapp requires specific code examples 1. Introduction With the popularity of mobile devices, more and more applications need to display various charts and animation effects on the mobile terminal. As a cross-platform development framework based on Vue.js, uniapp provides the ability to use canvas to draw charts and animation effects. This article will introduce how uniapp uses canvas to achieve chart and animation effects, and give specific code examples. 2. canvas
What properties does tkinter canvas have?
Aug 21, 2023 pm 05:46 PM
The tkinter canvas attributes include bg, bd, relief, width, height, cursor, highlightbackground, highlightcolor, highlightthickness, insertbackground, insertwidth, selectbackground, selectforeground, xscrollcommand attributes, etc. Detailed introduction
Explore the powerful role and application of canvas in game development
Jan 17, 2024 am 11:00 AM
Understand the power and application of canvas in game development Overview: With the rapid development of Internet technology, web games are becoming more and more popular among players. As an important part of web game development, canvas technology has gradually emerged in game development, showing its powerful power and application. This article will introduce the potential of canvas in game development and demonstrate its application through specific code examples. 1. Introduction to canvas technology Canvas is a new element in HTML5, which allows us to use
