js and canvas implement sliding puzzle verification code function
This article mainly shares with you js and canvas to implement the sliding puzzle verification code function. Nowadays, sliding puzzle verification is often encountered. I hope it can help everyone.
The picture above shows the sliding puzzle verification code of NetEase Cloud Shield. It should have a special picture library, and the cropping position is fixed. My idea is to randomly generate pictures, randomly generate positions, and then use canvas to cut out the sliders and background images. The specific steps are described below.
First find a random picture and render it on the canvas. Here #canvas is used as the canvas and #block is used as the cropped small slider.
<canvas width="310" height="155" id="canvas"></canvas> <canvas width="310" height="155" id="block"></canvas> var canvas = document.getElementById('canvas') var block = document.getElementById('block') var canvas_ctx = canvas.getContext('2d') var block_ctx = block.getContext('2d') var img = document.createElement('img') img.onload = function() { canvas_ctx.drawImage(img, 0, 0, 310, 155) block_ctx.drawImage(img, 0, 0, 310, 155) }; img.src = 'img.jpg'
Let’s consider how to cut out the shape of the puzzle. The shape of the puzzle is more complicated. First, we draw a square, and then write the above code :
var x = 150, y = 40, w = 42, r = 10, PI = Math.PI function draw(ctx) { ctx.beginPath() ctx.moveTo(x, y) ctx.lineTo(x + w, y) ctx.lineTo(x + w, y + w) ctx.lineTo(x, y + w) ctx.clip() } draw(canvas_ctx) draw(block_ctx)
The radius of the notched circle. We first encapsulate the drawing process with a function to facilitate the simultaneous operation of the background and slider later. Use the clip() method to crop the image to generate a square.
Next draw the circle on the top and right side of the square:
function draw(ctx) { ctx.beginPath() ctx.moveTo(x,y) + ctx.lineTo(x+w/2,y) + ctx.arc(x+w/2,y-r+2, r,0,2*PI) // + ctx.lineTo(x+w/2,y) ctx.lineTo(x+w,y) + ctx.lineTo(x+w,y+w/2) + ctx.arc(x+w+r-2,y+w/2,r,0,2*PI) // + ctx.lineTo(x+w,y+w/2) ctx.lineTo(x+w,y+w) ctx.lineTo(x,y+w) ctx.lineTo(x,y) ctx.clip() }
The position of the two annotations shifts the center of the circle 2px inward to achieve the gap style. Then there is the hollow part on the left. Since the clip is the part within the clipping path, it is not possible to draw a circle directly like above. We open a new path, and then draw a circle to "cover" a gap in the square, which will be used here. globalCompositeOperation attribute, 'xor' as the name suggests. The code continues from above:
function draw(ctx) { ctx.beginPath() ... ctx.lineTo(x,y) ctx.clip() + ctx.beginPath() + ctx.arc(x,y+w/2, r,1.5*PI,0.5*PI) // 只需要画正方形内的半圆就行,方便背景图片的裁剪 + ctx.globalCompositeOperation = "xor" + ctx.fill() }
Now that we have a basic puzzle shape, we adjust the size of #block and crop it Put the slider into #block:
img.onload = function() { ctx.drawImage(img, 0, 0, 310, 155) block_ctx.drawImage(img, 0, 0, 310, 155) + var blockWidth = w + r * 2 + var _y = y - r * 2 + 2 // 滑块实际的y坐标 + var ImageData = block_ctx.getImageData(x, _y, blockWidth, blockWidth) + block.width = blockWidth + block_ctx.putImageData(ImageData, 0, _y) }
Now we need to display the original picture on the left canvas and cut out the middle slider For the part, the process of drawing the path is the same here. The only difference is that clip() is changed to fill() to achieve the effect. We have encapsulated the process of drawing the path into a function before, and it can be changed slightly:
- function draw(ctx) { + function draw(ctx, operation) { ... - ctx.clip() + ctx.fillStyle = '#fff' + ctx[operation]() ... } + draw(canvas_ctx, 'fill') + draw(block_ctx, 'clip')
The next step is to write the style, skip it:
Then we write the drag event. We can record the mouse position when the mouse is pressed, and then set the left value for the slider when dragging. Finally, when you release the mouse, determine the left value of the slider at this time and the x value when the slider was first cropped. If it is within a certain range, the verification is passed, otherwise the verification fails.
Finally add random pictures and random cutting positions, and it’s basically ok. In addition, you can judge the change of the y-axis when the mouse moves to determine whether it is operated by a "human". Of course, web security is such a mess, so I won't go into details and just make a simple judgment.
Because there is no border or shadow added to the edge of the slice, the slider of some pictures is not highly identifiable and needs to be improved later (actually I haven't messed with it yet - -), I hope Someone who understands this can help me improve it //
Related recommendations:
How to create a simple verification code in php
PHP implementation code for verification code
The above is the detailed content of js and canvas implement sliding puzzle verification code function. For more information, please follow other related articles on the PHP Chinese website!

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.


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

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Atom editor mac version download
The most popular open source editor

SublimeText3 Linux new version
SublimeText3 Linux latest version

SublimeText3 Mac version
God-level code editing software (SublimeText3)

SublimeText3 English version
Recommended: Win version, supports code prompts!

SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.