HarmonyOS开发实战之XEngine Kit实现跨平台美颜特效

在开发"拍摄美颜相机"应用时，我们需要确保特效在不同设备上保持一致的渲染效果。今天重点记录XEngine Kit的应用实践，这个跨平台渲染引擎帮助我们轻松实现了OpenGL、Vulkan和Metal的多后端支持。

import { XEngine, BackendType } from '@ohos/xengine';

// 初始化引擎（自动选择最佳后端）
const engine = new XEngine({
  backendPreference: [BackendType.VULKAN, BackendType.GLES3],
  debug: false
});

// 创建渲染上下文
const context = engine.createContext({
  antialias: true,
  preserveDrawingBuffer: false
});

const beautyShader = engine.createShaderProgram({
  vertex: `
    attribute vec2 position;
    varying vec2 vUV;
    void main() {
      vUV = position * 0.5 + 0.5;
      gl_Position = vec4(position, 0.0, 1.0);
    }`,
  fragment: `
    precision highp float;
    uniform sampler2D inputTexture;
    uniform float smoothLevel;
    varying vec2 vUV;
    void main() {
      vec4 color = texture2D(inputTexture, vUV);
      // 简易磨皮算法
      gl_FragColor = vec4(mix(color.rgb, smoothstep(0.2, 0.8, color.rgb), smoothLevel), 1.0);
    }`
});

const pipeline = engine.createRenderPipeline({
  shader: beautyShader,
  vertexFormat: ['position:vec2'],
  textures: ['inputTexture']
});

// 更新美颜参数
pipeline.setUniform('smoothLevel', 0.75);

// 在工作线程初始化XEngine
workerEngine = new XEngine({
  backendType: BackendType.GLES3,
  sharedContext: mainContext
});

// 异步执行滤镜计算
workerPort.postMessage({
  type: 'processFrame',
  texture: frameTexture
});

// 检测设备温度过高时降级到GLES2
thermalMonitor.on('overheat', () => {
  engine.switchBackend(BackendType.GLES2);
});

engine.createTexture({
  width: ALIGN4(width),
  height: ALIGN4(height)
});

typescript
if (engine.currentBackend === BackendType.METAL) {
  setupMetalLayer(nativeView);
}