Canvas getcontext webgl. Syntax canvas. It's worth noting the WebGL render works fine in Chrome 63 on a Macbook. getContext('2d'); context. WebGLRenderingContext 接口提供基于 OpenGL ES 2. 14. Aug 26, 2024 · The getContext method is primarily used to access the 2D or 3D drawing context of an HTML canvas element. Nov 11, 2023 · I am developing an web app in ThreeJS (0. toDataURL('image/jpeg') and then post the data to the server. As of April 2014, there are two types of context that are available to you: 2d and webgl. getContext('webgl'); gl. Apr 3, 2025 · See getContext() for more information about the individual attributes. 0 rendering context for the drawing surface of an HTML <canvas> element. May 8, 2017 · The HTMLCanvasElement. This is more complex and beyond the scope of basic 2D usage. Includes performance benchmarks, use cases, and implementation examples. Only the options that are different from their defaults need to be The WebGLRenderingContext is an object that is used to issue WebGL rendering commands to a canvas. getContext() メソッドは、描画コンテキストを返します。対応していないコンテキスト識別子であったり、既に別なコンテキストモードが設定されていたりした場合は null になります。 You'll need to complete a few actions and gain 15 reputation points before being able to upvote. getContext () method returns a drawing context on the canvas, or null if the context identifier is not supported, or the canvas has already been set to a different context mode. Oct 28, 2024 · Getting started with WebGL Next WebGL enables web content to use an API based on OpenGL ES 2. Return value A WebGL extension object, or null if name does not match (case-insensitive) to one of the strings in WebGLRenderingContext. getContext('webgl', { desynchronized: true, preserveDrawingBuffer: true }); Flicker can also occur when you clear the screen context in your own drawing code. Jun 1, 2019 · How to know if a canvas is running a "WebGL" or just normal canvas? from inspecting the source, I find it a canvas in either case. The WebGL tutorial has more information, examples, and resources on how to get started with WebGL. Jul 23, 2025 · Step 2: Web Browser Ensure you have a modern web browser that supports WebGL, such as Google Chrome, Firefox, or Safari. Your job as a programmer using WebGL is to provide WebGL with those 2 things. getContext ('2d' or ctx=getContext (getContext ('webgl'). Jun 20, 2023 · I am trying to detect if the browser supports webgl. getContext('2d') 来获取，用于绘制 2D 图形，像矩形、圆形、文本、图像等。 WebGL 上下文：借助 canvas. I keep forgetting about the basic setup, Tagged with javascript, programming. Sep 15, 2023 · In JavaScript, the . It might be null if it is not associated with a <canvas> element or an OffscreenCanvas object. For example: var canvas = ; var ctx2d = canvas. getContext ('webgl2')! as RenderingContext2 // prints canvas as in Oct 26, 2024 · This method returns an ImageBitmap object, which can be used in a variety of Web APIs and also in a second canvas without creating a transfer copy. 0 to perform 2D and 3D rendering in an HTML canvas in browsers that support it without the use of plug-ins. getContext('webgl'); // will always be null The same is equally true if you reverse the order of calls. Feb 7, 2025 · Introduction WebGL™ is an immediate mode 3D rendering API designed for the web. There are 3 solutions. 1k次。WebGL上下文是从标签中获取到的，通过canvas对象的函数可以获取WebGLRenderingContext。跟据参数的不同，getContext ()函数可以获取不同种类的渲染上下文。'2d'WebGL1WebGL2canvas当为2dalpha当使用webglalphacanvasantialiasdepth"default"stencil当要获取一个上下文对象的时，可以使用接口来获取返回值 Free screencast video tutorials about WebGL for programmers and developers who like to learn. Jan 21, 2016 · 2. getContext('webgl', {preserveDrawingBuffer: true}); This makes webgl not clear the canvas after compositing the canvas with the rest of the page but prevents certain possible optimizations. 5 days ago · The OffscreenCanvas. For detailed information on the shader language used by WebGL, see the GLSL Specification. getContext ("webgl") returns null when testing with puppeteer and jest Asked 5 years, 6 months ago Modified 5 years, 6 months ago Viewed 1k times Here's the smallest WebGL program that actually does something const gl = document. getContext (‘webgl’) or canvas. when I draw a line on canvas#2 I want to copy drawn line on canvas#1 something like this: var context = canvas1. getContext('webgl2') can return null even though WebGL2RenderingContext exists #1738 hajimehoshi opened on Aug 1, 2021 Owner Jul 9, 2015 · I read about the canvas tag in HTML5, and always saw getContext('2d'). getImageData (), while for 'webgl' I would use ctx. This is probably the best option because a good browser could see that you have no alpha and actually optimize the way WebGL is composited. Sep 21, 2025 · This WebGL example explores the effect of setting (or not setting) the canvas size to its element size in CSS pixels, as it appears in the browser window. getContext("webgl", { alpha: false }}; This will make it act more like OpenGL since the backbuffer will only have RGB. canvas property is a read-only reference to the HTMLCanvasElement or OffscreenCanvas object that is associated with the context. ) For Jun 17, 2025 · The Canvas API provides a means for drawing graphics via JavaScript and the HTML <canvas> element. viewport tells WebGL how to convert from clip space (-1 to +1) back to pixels and where to do it within the canvas. getContext () method returns a drawing context on the canvas, or null if the context identifier is not supported. I was trying to switch context from 2d to webgl on the same canvas element. The failure is in the form of the console being overrun with the message: [Error] WebGL: context lost. Let me explain. A Vertex Oct 12, 2023 · However, the getContext ("2d") is only called for canvases pointed by references canvasRef and dynamicCanvasRef and the getContext ("webgl") is only called for canvas pointed by reference d3CanvasRef in above code. (See w3schools tutorial for more information. While Aug 1, 2021 · New issue Closed Closed canvas. Dec 31, 2019 · 2、然后又遇到了第二个问题，context获取为null 百度找了很多方法都没解决为什么context获取为空的原因，最后了解了一下laya发现，laya项目中有canvas模式和webgl模式，当是webgl模式的时候，通过canvas. :D Now, if you know what Jul 25, 2018 · The only question I have is if the canvas in the eventlistener supports getting a ctx=canvas. Among other things, it can be used for animation, game graphics, data visualization, photo manipulation, and real-time video processing. Later calls to this method on the same canvas element, with the same contextType argument, will always return the same drawing context instance as was returned the first time the method was invoked const gl = canvas. You can check WebGL support by visiting get. getContext () will always return that context independent of which 'webgl' or 'webgl2' Jul 20, 2016 · Assuming that I have a WebGL canvas (by calling getContext ("experimental-webgl")). Creating and Clearing the HTML Canvas In this first project, you will create an empty HTML5 canvas and clear the canvas to a specific color with WebGL. Feb 9, 2012 · WebGL Fundamentals WebGL makes it possible to display amazing realtime 3D graphics in your browser but what many people don't know is that WebGL is actually a 2D API, not a 3D API. To export the image I render the image into a canvas, export data via canvas. To get the WebGLRenderingContext object (or WebGL Drawing context object or simply WebGL context), call the getContext () method of the current HTMLCanvasElement. Aug 28, 2017 · create3DContext method just get null, and i found that canvas. A canvas element has a context. Jul 5, 2021 · WebGL通过引入一个与OpenGL ES 2. The HTMLCanvasElement. getContext() 方法返回canvas 的上下文，如果上下文没有定义则返回 null . The WebGLRenderingContext is obtained by passing 'webgl' to the HTMLCanvasElement. 03). Here’s an example that draws a simple square on a canvas. [Log] THREE. Alpha channels A translucent canvas element, one where alpha is set to true, can Sep 20, 2023 · 文章浏览阅读1. It is derived from OpenGL® ES 2. getContext() method. See WebGLContextAttributes for configuration options you can specify when calling getContext(). If it is '2d', I can use ctx. getContext("experimental-webgl") is essentially telling the browser, that the defined canvas is to be used exclusively by OpenGL/WebGL. If you must clear, draw to an offscreen framebuffer then copy that to the screen. To display the ImageBitmap, you can use an ImageBitmapRenderingContext context, which can be created by calling canvas. Is there any way to switch context later for using a "2d" one ? The goal of such thing would b May 14, 2025 · The WebGLRenderingContext. What's reputation and how do I get it? Instead, you can save this post to reference later. getContext('2d'); var ctx3d = canvas. 5 - Canvas and GL Context Graphics generated in real-time on a web page (as opposed to the display of a picture) are always drawn into a rectangular HTML canvas element. In short, the solution to your problem is to write: const gl = canvas. Step 3: Basic HTML Structure Create a simple HTML file with a <canvas> element where WebGL will render the graphics. It is built on top of the HTML5 canvas element, allowing you to utilize the GPU for complex rendering tasks. In the v3 code, I used getContext('2d') to get access to the canvas and getImageData() to get the pixel data (color RGB on a particular spot on the map). 3k次。文章讲述了在uniapp项目中使用JSMpeg库实时渲染监控视频时遇到的问题，由于预设canvas默认为2D，不能获取webglcontext。解决方案是动态创建canvas元素并将其添加到页面，确保其支持webgl。 Feb 24, 2022 · The CanvasElement associated with a RenderingContext2 when using webgl2 is missing: final actualCanvas = querySelector ('canvas')! as CanvasElement; final gl = actualCanvas. Apr 26, 2017 · This is expected, as webgl basically is a wrapper around opengl, primarily used for accelerated 3D rendering. getContext("webgl"); // Next we need to create vertex shaders - these roughly are small programs that apply maths to a set of incoming array of vertices (numbers). but it works well in the browers. getContext("bitmaprenderer") on a (visible) canvas element. HTMLCanvasElement. You provide 2 "shaders" to do this. Jul 2, 2025 · The HTMLCanvasElement. webgl. Perhaps you see harsh edges between areas with alpha = 0 and areas with non-zero alpha. Mar 31, 2014 · I start learning WebGL, and because i have found some old tutorials, i dont know what is the right way in 2014? I started the <canvas> (basic), and in tutorials they say something like: use Oct 16, 2024 · The WebGL2RenderingContext interface provides the OpenGL ES 3. getContext("webgl", { premultipliedAlpha: false }); But what is this Oct 30, 2022 · As the canvas is currently being used for WebGL, you cannot get another context from it: javascript - How to use multiple canvas contexts? - Stack Overflow 1 Like Ertugrul_Cetin October 30, 2022, 5:14pm 3 Jun 1, 2023 · Create a new canvas with a 2d context and copy the pixeldata from the webgl canvas using drawImage() Using the WEBGL_lose_context extension, get rid of the old webgl context Wait until it emits the webglcontextlost event, so you know it's save to create a new webgl context Replace the old canvas with the webgl context by the just copied clone May 25, 2025 · A comprehensive comparison guide to help you choose between WebGL and Canvas for your web graphics projects. 2w次，点赞10次，收藏36次。本文详细介绍了HTMLCanvasElement的getContext ()方法，包括2D、WebGL及WebGL2的渲染上下文创建方式与属性设置，适用于不同类型的图形渲染需求。 Mar 22, 2018 · WebGL Context Options The first step to create 3D graphics in a HTML canvas is to retrieve a WebGL context object, WebGLRenderingContext, by calling canvas. getContext (‘experimental-webgl’) for 3D rendering via WebGL. viewport to set the viewport. There is an API for creating 2D graphics which we won’t take time to discuss here. ) For WebGL The HTMLCanvasElement. 简述 要编写 WebGL 应用程序，第一步是获取 WebGL 渲染上下文对象。该对象与 WebGL 绘图缓冲区交互，可以调用所有 WebGL 方法。执行以下操作以获得 WebGL 上下文 - 创建 HTML-5 Canvas 获取Canvas ID 获取WebGL 创建 HTML-5 Can The HTMLCanvasElement. COLOR_BUFFER_BIT); All this program does is clear the canvas to red but it did actually do something. The parameter is '2d', so isn't there another possibility like '3d'? And, how could you use that? I tried 3D before, but didn't #2) Tell WebGL you don't want alpha in the backbuffer gl = canvas. getContext ('experimental_webgl', {}) both get null in the electron webview. There’s several easy-to-miss differences between how WebGL and WebGPU behave, though, that can lead to an inaccurate comparisons if not taken into account. getContext() method returns a drawing context on the canvas, or null if the context identifier is not supported. 0. With just this you can actually test some things. Oct 16, 2017 · Is a decent way to use it in a typesafe way without really getting in the way; but if you must remove null from the type definition, you should probably only remove it from the overloads for "2d" and "webgl" (and I guess there should be one for "bitmaprenderer"), but not the base signature with string. Jun 4, 2024 · Introduction If you are developing a WebGPU variant of an existing WebGL application it’s natural to want to benchmark the two to determine either where performance needs to be improved or how much faster one is relative the other. getContext('2d'); From there you can begin drawing, filling and stroking shapes and text on the canvas. : ( The HTMLCanvasElement. WebGLRenderer: Context Lost const gl = canvas. getContext() method returns a drawing context on the canvas, or null if the context identifier is not supported, or the canvas has already been set to a different context mode. 3 and iPad at iPadOS 17. "webgl" creates a WebGLRenderingContext object representing a three-dimensional rendering Jan 1, 2017 · To display the ImageBitmap, you can use a ImageBitmapRenderingContext context, which can be created by calling canvas. The context defines how the graphics are created. getSupportedExtensions. Jan 21, 2016 · Now that we have an object that represents the canvas element, we use a method of the object called getContext('webgl') to get a WebGL object that represents the 3D graphics state and behavior of the canvas. 0 的绘图上下文，用于在 HTML <canvas> 元素内绘图。 要获得这个接口的对象以用于 2D 和 3D 的图形渲染，可以通过在 <canvas> 元素上调用 getContext() 函数，调用时传入“webgl”参数：. canvas. getExtension () method enables a WebGL extension. 0, and provides similar rendering functionality, but in an HTML context. drawImage(canvas2,0,0); but because my canvas#1 has a getContext ('webgl') I can't do that. getContext('webgl')：从 <canvas> 元素中获取 WebGL 上下文对象 gl，后续的 WebGL 操作都将基于这个上下文对象进行。 1. clear(gl. Think about it through. Examples Once a WebGL extension is enabled, you are able to use the methods, properties Jan 20, 2023 · It's a very fun time every time I start a new WebGL project. With Maps SDK, it seems the map is drawn on a we HTMLCanvasElement. querySelector('canvas'), ctx = canvas. getContext('webgl') 或 canvas. getContext(contextType, contextAttributes); Parameters contextType Is a DOMString containing the context identifier defining the drawing context associated to the canvas. May 2, 2019 · const canvas = document. 1. この記事の概要 HTML, CSS だけと比べて、WebGL を用いると表現力がアップします。 しかし WebGL や canvas に関連する記事が割と少なく、頑張って学んでいる最中です。 学んだ内容について、備忘録を兼ねて記事を書いていきます。 canvas 要素は、 #2) Tell WebGL you don’t want alpha in the backbuffer gl = canvas. Oct 23, 2020 · I have a WebGL canvas which I want to clear at a certain point which uses a WebGL2RenderingContext and I can't seem to find a way to either: Clear the canvas Replace the context with a different c Aug 15, 2019 · 上面的代码，canvas对象已经获取过webgl上下文，再获取2d上下文，就会返回null。 👉🏻 getContext获取上下文有第二个参数 To create a WebGL rendering context on the canvas element, you should pass the string experimental-webgl, instead of 2d to the canvas. Saving the state of the graphics machine within a single context Syntax offscreen. org. my env is win7 64bit "electron" Sep 26, 2020 · webgl中的getContext ()方法和canvas中的有什么区别？ 如何判断getContext ()方法获取上下文是否成功？ 该系列总览: Hadoop3. When you first create the WebGL context WebGL will set the viewport to match the size of the canvas but after Syntax offscreen. To get an object of this interface, call getContext() on a <canvas> element, supplying "webgl" as the argument: var canvas = document. Sep 12, 2025 · 文章浏览阅读3. Mar 6, 2021 · 问题描述 canvas经过封装之后，变成了uni-canvas，这样其他插件通过canvas获取webgl的时候，就会报无法获取，请问如何处理 复现步骤 目前使用jsmpeg插件，插件内有一段代码是通过canvas对象获取webgl的，这时候首先会报 this. getContext () method. Sep 21, 2025 · In this first example we are going to check whether the browser supports WebGL. WebGL programs consist of control code written in JavaScript and shader code (GLSL) that is executed on a computer's Graphics Processing Unit (GPU). Some browsers support only ' webgl '. 1架构体系——设计原理阐述与Client源码图文详解 : 总览 在 HDFS 中，有三种Recovery 1. Specifications Specification WebGL Specification # 5. Block Recovery 3. We initialize the WebGL context, clear the canvas with a default color, and provide a button to change the canvas color interactively. 2 初始化 着色器 着色器是 WebGL 中用于处理图形渲染的程序，分为顶点着色器和片元着色器。我们需要将 I am attempting to detect WebGL support across multiple browsers and I've encountered the following scenario. The getContext function is the function that you use to get access to the canvas tags 2D drawing functions. gl. Possible values are: "2d ", leading to the creation of a CanvasRenderingContext2D object representing a two-dimensional rendering context. Lease Recovery 2. To begin drawing on the canvas, you grab hold of it and retrieve a particular context - either 2d or webgl: var canvas = document. Possible values are: "2d ", leading to the creation of a Jun 15, 2021 · // BUG: Workaround Safari WebGL issue: After successfully acquiring WebGL context on a canvas, // calling . Clipspace coordinates in 2D and colors. getContext('webgl'); Once you have the WebGL rendering context for a canvas, you can What is WebGL? WebGL was created in 2011. getContext is not a function The HTMLCanvasElement. 2 Mar 21, 2018 · 2. Jun 8, 2017 · The WebGLRenderingContext interface provides the OpenGL ES 2. getContext('webgl', options). clearColor(1, 0, 0, 1); // red gl. js for rendering, if I use canvas renderer then everything works on the server; It's WebGL rendering thats not working. readPixels () to get a specific target pixel region. "webgl" which will create a WebGLRenderingContext object representing May 30, 2025 · 2D 上下文：通过 canvas. ) If you are trying Aug 12, 2020 · Why does my WebGL alpha-transparency look wrong? When using WebGL and creating a partially transparent canvas, you may have noticed that the transparency looks wrong. 0), as part of a conversion from WebGL code, but while the scene renders in Chrome and Safari on my Mac it fails on both my iPhone and iPad, using iOS 17 (iPhone 12 Pro at 17. WebGL only cares about 2 things. Possible values are: "2d" creates a CanvasRenderingContext2D object representing a two-dimensional rendering context. Plus, it can be used alongside old WebGL code. This The code won't work since you use the same canvas object for getContext() in all cases. (It is possible to use OpenGL/WebGL for 2D, but unless you know what you are doing, you're giving yourself a hard time in doing so. getContext ('webgl', {}) or canvas. WebGL is designed as a rendering context for the HTML Canvas element. You detect it by creating a canvas object on the document and then getting the context to see if it is "webgl" or "experimental-webgl". The HTML Canvas provides a destination for programmatic rendering in web pages, and allows for performing that rendering using different The issue is that for performance and compatibility reasons, by default the browser will clear a WebGL canvas’s drawing buffer after you’ve drawn to it. The tests must be performed on different elements than the one you intend to actually use, which means you have to create a new canvas element instance before each getContext() as @tommie showed in his now deleted answer (running the snippet was evidence of 此参数可以返回一个 WebGLRenderingContext （WebGL渲染上下文） 对象，WebGL（全写Web Graphics Library）是一种3D绘图协议，可以为HTML5 Canvas提供硬件3D加速渲染，这样Web开发人员就可以借助系统显卡来在浏览器里更流畅地展示3D场景和模型，无需安装任何其他插件。 Sep 30, 2024 · Hello, I'm migrating a web mapping application from ESRI Javascript API v3 to ArcGIS Maps SDK v4. The most important things about it is that it’s modern, simple and widely supported. Setup - WebGL 2 context initialization We’re not gonna be jumping into WebXR just yet, first we have to figure out, how will we actually draw our scenes? Well, for that we will use WebGL 2. getContext () method is commonly used with the HTML5 <canvas> element to obtain a 2D drawing context or a WebGL rendering context for that canvas. The WebGL rendering context is an interface, through which you can set and query the state of the graphics machine, send data to the WebGL, and execute draw commands. This context provides the necessary tools and properties for drawing graphics, shapes The HTMLCanvasElement. Sep 25, 2024 · When you see a <canvas> element on a web page what is the super fast way to find if it's created using 2d or WebGL context? Mar 9, 2021 · As has been found in emscripten-core/emscripten#13497 and emscripten-core/emscripten#13295 , and pointed out by @kainino0x , the canvas getContext specification at: 微信开发者平台文档# RenderingContext Canvas. Aug 6, 2024 · In this approach, we are using the getContext method directly to create a WebGL context on a canvas element. Later calls to this method on the same canvas element return the same drawing context instance as was returned the last time the method was invoked with the same contextType argument. The current version of Firefox appears to report positive support using the following c Sep 20, 2019 · canvas. WebGL elements can be mixed with other HTML const gl = someCanvas. getContext('webgl2') || canvas. Upvoting indicates when questions and answers are useful. querySelector('myCanvas'); const ctx = canvas. For others who hit this page while searching for getContext returning null, it can happen if you have already requested a different type of context. getContext ('2d')自然是获取不到的，修改写法： Jan 6, 2025 · WebGL context: Request using canvas. It was designed as a Web API to provide 2D and 3D drawing inside an HTML canvas element, without the use of a browser plug-in. PipeLine Recovery 以下将 一 一 讲解。 Dec 14, 2024 · WebGL is a powerful graphics API that allows you to render 3D graphics directly within the browser. getContext('webgl'); This allows you to provide the best possible experience based on the user’s hardware capabilities, without excluding users on older devices. 157. 0非常一致的API来做到这一点，该API可以在HTML5 <canvas>元素中使用。 这种一致性使API可以利用用户设备提供的 硬件图形加速 (与canvas 2D区别)。 Dec 26, 2016 · Calling getContext with "2d" returns a CanvasRenderingContext2D object, whereas calling it with "experimental-webgl" (or "webgl") returns a WebGLRenderingContext object. querySelector('canvas')：通过选择器获取 HTML 文档中的 <canvas> 元素。 canvas. May 3, 2019 · Omg, thanks for a super explanation. Jul 24, 2023 · 获取WebGL上下文 获取上下文 WebGL上下文是从 <canvas> 标签中获取到的，通过 canvas 对象的 getContext() 函数可以获取 WebGLRenderingContext。 跟据参数的不同， getContext() 函数可以获取不同种类的渲染上下文。 接口 canvas. Oct 9, 2024 · Once you have the WebGL rendering context for a canvas, you can render within it. The options parameter sets properties of the “context” at the time of its creation. I'm using Pixi. To that end we will try to obtain the WebGL rendering context from a canvas element. 6 I have a canvas for showing medical image and I have another canvas for annotating images by draw shape or line. WebGL2 is a web API that links to OpenGLES3. getContext (string contextType, Object contextAttributes) 微信 鸿蒙 OS 版：支持 # 功能描述 获取画布对象的绘图上下文 # 参数 # string contextType 上下文类型 contextType 的合法值 解释： document. getContext(contextType: String, contextAttributes ?: Object) contextType: '2d'：建立一个 CanvasRenderingContext2D Hey, something is wrong? Why is the line not covering the entire area? The reason is when we resize the canvas we also need to call gl. To get a different drawing context object you need to pass a different Jul 1, 2025 · The WebGLRenderingContext. getContext() method returns a drawing context for an offscreen canvas, or null if the context identifier is not supported, or the offscreen canvas has already been set to a different context mode. 5 - Canvas and GL Context ¶ Graphics generated in real-time on a web page (as opposed to the display of a picture) are always drawn into a rectangular HTML canvas element. getElementById('myCanvas'); var gl = canvas. Parameters name A String for the name of the WebGL extension to enable. getContext('webgl2') 获取，用于绘制 3D 图形，在游戏、数据可视化等领域应用广泛。 浏览器对上下文对象的支持情况 2D Sep 10, 2025 · 文章浏览阅读2. querySelector('canvas'). 9vqe ldomyr dnyac1 3nv9b ke46h apoh jff o80i s46xoi wxj