Implementation of custom rendering logic

Understanding the Core Concepts of Custom Rendering Logic

Vue3's custom rendering logic allows developers to bypass the default DOM rendering approach and achieve rendering control in specific scenarios. This capability comes from the renderer API exposed in the @vue/runtime-core package. By creating a custom renderer, we can render Vue components to non-DOM environments.

import { createRenderer } from '@vue/runtime-core'

const { render, createApp } = createRenderer({
  patchProp,
  insert,
  remove,
  createElement,
  // ...other node operation methods
})

Analysis of the Renderer Creation Process

The core of creating a custom renderer is the createRenderer function, which accepts a configuration object containing node operation methods. These methods define how to create, update, and delete rendering targets. For example, in a Canvas rendering scenario:

function createCanvasElement(tag) {
  if (tag === 'circle') {
    return new Circle()
  } else if (tag === 'rect') {
    return new Rectangle()
  }
  // Other graphic types
}

const canvasRenderer = createRenderer({
  createElement: createCanvasElement,
  insert(child, parent) {
    parent.addChild(child)
  },
  patchProp(el, key, prevValue, nextValue) {
    el.setAttribute(key, nextValue)
  }
})

Conversion from Virtual Nodes to Specific Platforms

Vue's virtual DOM needs to be converted into rendering instructions for specific platforms. In a WebGL renderer, a vnode might correspond to the creation of a shader program:

function mountComponent(vnode, container) {
  const instance = createComponentInstance(vnode)
  if (vnode.type === 'mesh') {
    const geometry = new THREE.BufferGeometry()
    const material = new THREE.MeshBasicMaterial()
    instance.subTree = new THREE.Mesh(geometry, material)
    container.add(instance.subTree)
  }
  // Handling other component types
}

Differential Handling of Property Updates

Custom renderers need to handle special logic for property updates. For example, in a PDF rendering scenario, text style updates require recalculating the layout:

function patchProp(el, key, prevValue, nextValue) {
  if (key === 'fontSize') {
    el.fontSize = nextValue
    recalculateLayout(el)
  } else if (key === 'color') {
    el.fillColor = hexToPDFColor(nextValue)
  }
  // Handling other properties
}

Component Lifecycle and Rendering Timing

Custom renderers need to precisely control the relationship between component lifecycles and rendering timing. In a server-side rendering scenario:

const serverRenderer = createRenderer({
  createElement() { /* no-op */ },
  insert() { /* no-op */ },
  patchProp() { /* no-op */ },
  beforeUpdate(component) {
    // No actual update operations are needed on the server
    return false
  }
})

Implementation of Cross-Platform Event Systems

Event handling is a key part of custom rendering. In mobile native rendering:

function addEventListener(el, event, handler) {
  if (event === 'click') {
    el.onPress = (nativeEvent) => {
      const syntheticEvent = createSyntheticEvent(nativeEvent)
      handler(syntheticEvent)
    }
  }
  // Other event types
}

Performance Optimization Strategies

Custom renderers can implement platform-specific performance optimizations. For example, in a game engine:

function shouldUpdateComponent(prevVNode, nextVNode) {
  // Skip updates for static scene objects
  if (prevVNode.type.isStaticSceneObject) {
    return false
  }
  // Regular diff logic
  return !Object.is(prevVNode.props, nextVNode.props)
}

Composition API and Rendering Logic

The Composition API can better integrate with custom rendering logic. In a WebXR scenario:

export function useXRController() {
  const controller = ref(null)
  
  onMounted(() => {
    controller.value = renderer.xr.getController(0)
    scene.add(controller.value)
  })
  
  return { controller }
}

Testing Custom Renderers

Testing custom renderers requires simulating the platform environment:

describe('PDF renderer', () => {
  let pdfDoc, renderer
  
  beforeEach(() => {
    pdfDoc = new PDFDocument()
    renderer = createPDFRenderer(pdfDoc)
  })
  
  it('should render text nodes', () => {
    renderer.render(h('text', { fontSize: 12 }, 'Hello'))
    expect(pdfDoc.textContent).toContain('Hello')
  })
})

Case Studies of Practical Applications

Implementing custom rendering in an electronic whiteboard application:

const whiteboardRenderer = createRenderer({
  createElement(type) {
    if (type === 'stroke') {
      return new StrokePath()
    }
    // Other whiteboard element types
  },
  insert(el, parent) {
    parent.addElement(el)
    whiteboard.redraw()
  }
})

const app = createApp(App).use(whiteboardRenderer)
app.mount('#whiteboard')