绘制笔画

为了获得最佳绘图性能，请使用startStroke()、addToStroke()和finishStroke() InProgressStrokesView类的 方法，并将MotionEvent对象作为输入传递。

  1. 设置 UI 组件

    将InProgressStrokesView集成到你的视图层次结构中。

    <FrameLayout>

  <ScrollView
    android:id="@+id/my_content"
    android:width="match_parent"
    android:height="match_parent"
    >
    <!-- Your content here. -->
  </ScrollView>

  <androidx.ink.authoring.InProgressStrokesView
    android:id="@+id/in_progress_strokes_view"
    android:width="match_parent"
    android:height="match_parent"
    />

</FrameLayout>

  2. 实例化 InProgressStrokesView

    在你的活动或片段的[onCreate()][ink-draw-include6]方法中，获取对InProgressStrokesView的引用，并建立一个触摸监听器来管理用户输入。

    class MyActivity : View.OnTouchListener {
    private lateinit var contentView: ScrollView
    private lateinit var inProgressStrokesView: InProgressStrokesView
    private lateinit var predictor: MotionEventPredictor

    // ... other variables

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
      predictor = MotionEventPredictor.newInstance(contentView)
        contentView = findViewById(R.id.my_content)
        contentView.setOnTouchListener(touchListener)
        inProgressStrokesView = findViewById(R.id.in_progress_strokes_view)
    }

    // ... (touchListener implementation)
}

  3. 处理触摸事件

    建立UI组件后，您现在可以根据触摸事件启动绘图。

    MotionEvent 动作

    InProgressStrokesView 方法

    描述

    ACTION_DOWN

    startStroke()

    开始笔画渲染

    ACTION_MOVE

    addToStroke()

    继续渲染笔画

    ACTION_UP

    finishStroke()

    完成笔画渲染

    ACTION_CANCEL 或 FLAG_CANCELED

    cancelStroke()

    实现手掌拒绝；取消笔画

    		 

    class MyActivity : View.OnTouchListener {
  private lateinit var contentView: ScrollView
  private lateinit var inProgressStrokesView: InProgressStrokesView

  private var pointerId = -1
  private var strokeId: InProgressStrokeId? = null
  private lateinit var predictor: MotionEventPredictor

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    contentView = findViewById(R.id.my_content)
    predictor = MotionEventPredictor.create(contentView)
    contentView.setOnTouchListener(touchListener)
    inProgressStrokesView = findViewById(R.id.in_progress_strokes_view)
  }

  private val touchListener = { view: View, event: MotionEvent ->
    predictor.record(event)
      when (event.actionMasked) {
        MotionEvent.ACTION_DOWN -> {
          // First pointer - treat it as inking.
          view.requestUnbufferedDispatch(event)
          val pointerIndex = event.actionIndex
          pointerIdToStrokeId[event.getPointerId(pointerIndex)] =
            inProgressStrokesView.startStroke(event, pointerId)
          return true
        }
        MotionEvent.ACTION_POINTER_DOWN -> {
          val stroke = strokeId ?: return false
          inProgressStrokesView.cancelStroke(stroke, event)
          strokeId = null
          pointerId = -1
          return false
        }
        MotionEvent.ACTION_MOVE -> {
          val predictedEvent = predictor.predict()
          try
          {
            for (pointerIndex in 0 until pointerCount) {
              val strokeId =
              pointerIdToStrokeId[event.getPointerId(pointerIndex)] ?: continue
              inProgressStrokesView.addToStroke(event, pointerId, strokeId, predictedEvent)
            } finally {
              predictedEvent?.recycle()
            }
          }
        }
        MotionEvent.ACTION_UP -> {
          val pointerIndex = event.actionIndex
          val strokeId =
            pointerIdToStrokeId[event.getPointerId(pointerIndex)] ?: return false
          inProgressStrokesView.finishStroke(event, pointerId, strokeId)
          return true
        }
        MotionEvent.ACTION_CANCEL -> {
          val pointerIndex = event.actionIndex
          val strokeId =
            pointerIdToStrokeId[event.getPointerId(pointerIndex)] ?: return false
          inProgressStrokesView.cancelStroke(strokeId, event)
          return true
        }
      }
    return false
  }
}

  4. 处理已完成的笔画

    调用finishStroke()后，笔画将被标记为已完成。但是，完成过程并非即时完成。笔画在finishStroke()调用后不久完全处理并可供你的应用程序访问，具体来说是在没有其他笔画正在进行时。这确保了所有绘图操作在笔画作为已完成状态移交给客户端之前都已结束。

    要检索已完成的笔画，你有两种选择

    class MyActivity : ComponentActivity(), InProgressStrokesFinishedListener {
  ...

  private val finishedStrokesState = mutableStateOf(emptySet<Stroke>())

  override fun onCreate(savedInstanceState: Bundle?) {
    ...
    inProgressStrokesView.addFinishedStrokesListener(this)
  }

  // ... (handle touch events)

  @UiThread
  override fun onStrokesFinished(strokes: Map<InProgressStrokeId, Stroke>) {
    finishedStrokesState.value += strokes.values
    inProgressStrokesView.removeFinishedStrokes(strokes.keys)
  }
}

    检索到已完成的笔画后，你可以使用ViewStrokeRenderer作为构建在CanvasStrokeRenderer之上的更高级别的抽象。这可以进一步简化你的视图层次结构中的渲染过程。

    class DrawingView(context: Context) : View(context) {
  private val viewStrokeRenderer = ViewStrokeRenderer(myCanvasStrokeRenderer, this)

  override fun onDraw(canvas: Canvas) {
    viewStrokeRenderer.drawWithStrokes(canvas) { scope ->
      canvas.scale(myZoomLevel)
      canvas.rotate(myRotation)
      canvas.translate(myPanX, myPanY)
      scope.drawStroke(myStroke)
      // Draw other objects including more strokes, apply more transformations, ...
    }
  }
}