Expo GLView

提供 GLView 的库，充当 OpenGL ES 渲染目标并提供 GLContext。对于渲染 2D 和 3D 图形很有用。

expo-gl 提供了充当 OpenGL ES 渲染目标的 View，对于渲染 2D 和 3D 图形很有用。安装时，会创建 OpenGL ES 上下文。其绘图缓冲区每帧渲染为 View 的内容。

¥expo-gl provides a View that acts as an OpenGL ES render target, useful for rendering 2D and 3D graphics. On mounting, an OpenGL ES context is created. Its drawing buffer is presented as the contents of the View every frame.

安装

¥Installation

If you are installing this in an existing React Native app (bare workflow), start by installing expo in your project. Then, follow the additional instructions as mentioned by library's README under "Installation in bare React Native projects" section.

用法

¥Usage

import React from 'react';
import { View } from 'react-native';
import { GLView } from 'expo-gl';

export default function App() {
  return (
    <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
      <GLView style={{ width: 300, height: 300 }} onContextCreate={onContextCreate} />
    </View>
  );
}

function onContextCreate(gl) {
  gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
  gl.clearColor(0, 1, 1, 1);

  // Create vertex shader (shape & position)
  const vert = gl.createShader(gl.VERTEX_SHADER);
  gl.shaderSource(
    vert,
    `
    void main(void) {
      gl_Position = vec4(0.0, 0.0, 0.0, 1.0);
      gl_PointSize = 150.0;
    }
  `
  );
  gl.compileShader(vert);

  // Create fragment shader (color)
  const frag = gl.createShader(gl.FRAGMENT_SHADER);
  gl.shaderSource(
    frag,
    `
    void main(void) {
      gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
    }
  `
  );
  gl.compileShader(frag);

  // Link together into a program
  const program = gl.createProgram();
  gl.attachShader(program, vert);
  gl.attachShader(program, frag);
  gl.linkProgram(program);
  gl.useProgram(program);

  gl.clear(gl.COLOR_BUFFER_BIT);
  gl.drawArrays(gl.POINTS, 0, 1);

  gl.flush();
  gl.endFrameEXP();
}

高级 API

¥High-level APIs

由于 WebGL API 的级别相当低，因此通过下面的 GLView 使用更高级别的图形 API 渲染会很有帮助。以下库集成了流行的图形 API：

¥Since the WebGL API is quite low-level, it can be helpful to use higher-level graphics APIs rendering through a GLView underneath. The following libraries integrate popular graphics APIs:

• expo-three 换 three.js

  ¥expo-three for three.js

• expo-processing 换 processing.js

  ¥expo-processing for processing.js

任何需要 WebGLRenderingContext 的 WebGL 支持库都可以使用。有时，此类库会假设一个 Web JavaScript 上下文（例如假设 document）。通常这是为了资源加载或事件处理，主要渲染逻辑仍然只使用纯 WebGL。因此，这些库通常仍然可以通过一些解决方法来使用。上面针对 Expo 的集成包括一些流行库的解决方法。

¥Any WebGL-supporting library that expects a WebGLRenderingContext could be used. Some times such libraries assume a web JavaScript context (such as assuming document). Usually this is for resource loading or event handling, with the main rendering logic still only using pure WebGL. So these libraries can usually still be used with a couple workarounds. The Expo-specific integrations above include workarounds for some popular libraries.

与 Reanimated 工作集集成

¥Integration with Reanimated worklets

要在 Reanimated 工作集中使用此 API，你需要将 GL 上下文 ID 传递给工作集并重新创建 GL 对象，如下例所示。

¥To use this API inside Reanimated worklet, you need to pass the GL context ID to the worklet and recreate the GL object like in the example below.

import React from 'react';
import { View } from 'react-native';
import { runOnUI } from 'react-native-reanimated';
import { GLView } from 'expo-gl';

function render(gl) {
  'worklet';
  // add your WebGL code here
}

function onContextCreate(gl) {
  runOnUI((contextId: number) => {
    'worklet';
    const gl = GLView.getWorkletContext(contextId);
    render(gl);
  })(gl.contextId);
}

export default function App() {
  return (
    <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
      <GLView
        style={{ width: 300, height: 300 }}
        enableExperimentalWorkletSupport
        onContextCreate={onContextCreate}
      />
    </View>
  );
}

有关如何将 expo-gl 与 Reanimated 和 Gesture Handler 一起使用的更深入示例，你可以查看 这个例子。

¥For more in-depth example on how to use expo-gl with Reanimated and Gesture Handler you can check this example.

局限性

¥Limitations

Worklet 运行时对其内部运行的代码施加了一些限制，因此，如果你有现有的 WebGL 代码，则可能需要进行一些修改才能在 Worklet 线程内运行。

¥Worklet runtime is imposing some limitations on the code that runs inside it, so if you have existing WebGL code, it'll likely require some modifications to run inside a worklet thread.

• Pixi.js 或 Three.js 等第三方库无法在工作集中运行，你只能使用开头添加了 'worklet' 的函数。

  ¥Third-party libraries like Pixi.js or Three.js won't work inside the worklet, you can only use functions that have 'worklet' added at the start.

• 如果你需要加载一些资源以传递给 WebGL 代码，则需要在主线程上完成并通过对工作集的某些引用传递。如果你使用 expo-assets，则只需将 Asset.fromModule 返回的资源对象或从钩子 useAssets 传递到 runOnUI 函数即可。

  ¥If you need to load some assets to pass to the WebGL code, it needs to be done on the main thread and passed via some reference to the worklet. If you are using expo-assets you can just pass asset object returned by Asset.fromModule or from hook useAssets to the runOnUI function.

• 要实现渲染循环，你需要使用 requestAnimationFrame，不支持像 setTimeout 这样的 API。

  ¥To implement a rendering loop you need to use requestAnimationFrame, APIs like setTimeout are not supported.

• 它仅在 Android 和 iOS 上受支持，在 Web 上不起作用。

  ¥It's supported only on Android and iOS, it doesn't work on Web.

检查 复活的文档 以了解更多信息。

¥Check Reanimated documentation to learn more.

远程调试和 GLView

¥Remote debugging and GLView

启用远程调试后，此 API 无法按预期运行。React Native 调试器在你的计算机上运行 JavaScript，而不是在移动设备上。GLView 需要 Chrome 不支持的同步原生调用。

¥This API does not function as intended with remote debugging enabled. The React Native debugger runs JavaScript on your computer, not the mobile device. GLView requires synchronous native calls that are not supported in Chrome.

API

import { GLView } from 'expo-gl';

Component

Static Methods

Component Methods

Methods

Interfaces

Types

Enums

WebGL API

安装组件并创建 OpenGL ES 上下文后，通过 onContextCreate 属性接收的 gl 对象将成为 OpenGL ES 上下文的接口，提供 WebGL API。它类似于 WebGL 2 规范中的 WebGL2 渲染上下文。

¥Once the component is mounted and the OpenGL ES context has been created, the gl object received through the onContextCreate prop becomes the interface to the OpenGL ES context, providing a WebGL API. It resembles a WebGL2RenderingContext in the WebGL 2 spec.

某些较旧的 Android 设备可能不支持 WebGL2 功能。要检查设备是否支持 WebGL2，建议使用 gl instanceof WebGL2RenderingContext。

¥Some older Android devices may not support WebGL2 features. To check whether the device supports WebGL2 it's recommended to use gl instanceof WebGL2RenderingContext.

存在附加方法 gl.endFrameEXP()，其通知上下文当前帧已准备好渲染。这类似于其他 OpenGL 平台中的 '交换缓冲区' API 调用。

¥An additional method gl.endFrameEXP() is present, which notifies the context that the current frame is ready to present. This is similar to a 'swap buffers' API call in other OpenGL platforms.

以下 WebGL2RenderingContext 方法当前未实现：

¥The following WebGL2RenderingContext methods are currently unimplemented:

• getFramebufferAttachmentParameter()

• getRenderbufferParameter()

• compressedTexImage2D()

• compressedTexSubImage2D()

• getTexParameter()

• getUniform()

• getVertexAttrib()

• getVertexAttribOffset()

• getBufferSubData()

• getInternalformatParameter()

• renderbufferStorageMultisample()

• compressedTexImage3D()

• compressedTexSubImage3D()

• fenceSync()

• isSync()

• deleteSync()

• clientWaitSync()

• waitSync()

• getSyncParameter()

• getActiveUniformBlockParameter()

texImage2D() 的 pixels 参数必须是 null、具有像素数据的 ArrayBuffer 或 { localUri } 形式的对象，其中 localUri 是设备文件系统中图片的 file:// URI。因此，一旦调用了 .downloadAsync()（并完成）来获取资源，就会使用 Asset 对象。

¥The pixels argument of texImage2D() must be null, an ArrayBuffer with pixel data, or an object of the form { localUri } where localUri is the file:// URI of an image in the device's file system. Thus, an Asset object is used once .downloadAsync() has been called on it (and completed) to fetch the resource.

出于效率原因，这些方法的当前实现不会对其参数执行类型或边界检查。因此，传递无效参数可能会导致原生崩溃。计划更新 API 以在即将推出的 SDK 版本中执行参数检查。

¥For efficiency reasons, the current implementations of the methods don't perform type or bounds checking on their arguments. So, passing invalid arguments may cause a native crash. There are plans to update the API to perform argument checking in upcoming SDK versions.

目前，错误检查的优先级较低，因为引擎通常不依赖 OpenGL API 来执行参数检查；否则，由底层 OpenGL ES 实现执行的检查通常就足够了。

¥Currently, the priority for error checking is low since engines generally don't rely on the OpenGL API to perform argument checking; otherwise, checks performed by the underlying OpenGL ES implementation are often sufficient.