LowLatencyCanvasView

@RequiresApi(value = 29)
public final class LowLatencyCanvasView extends ViewGroup

import androidx.annotation.WorkerThread
import androidx.graphics.lowlatency.LowLatencyCanvasView

LowLatencyCanvasView(context).apply {
    setBackgroundColor(Color.WHITE)

    data class Line(
        val x1: Float,
        val y1: Float,
        val x2: Float,
        val y2: Float,
    )
    // Thread safe collection to support creation of new lines from the UI thread as well as
    // consumption of lines from the background drawing thread
    val lines = Collections.synchronizedList(ArrayList<Line>())
    setRenderCallback(object : LowLatencyCanvasView.Callback {

        val mAllLines = ArrayList<Line>()

        private val mPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
            strokeWidth = 15f
            color = Color.CYAN
            alpha = 128
        }

        @WorkerThread
        override fun onRedrawRequested(
            canvas: Canvas,
            width: Int,
            height: Int
        ) {
            for (line in mAllLines) {
                canvas.drawLine(line.x1, line.y1, line.x2, line.y2, mPaint)
            }
        }

        @WorkerThread
        override fun onDrawFrontBufferedLayer(
            canvas: Canvas,
            width: Int,
            height: Int
        ) {
            lines.removeFirstOrNull()?.let { line ->
                mAllLines.add(line)
                canvas.drawLine(line.x1, line.y1, line.x2, line.y2, mPaint)
            }
        }
    })
    setOnTouchListener(object : View.OnTouchListener {

        var mCurrentX = -1f
        var mCurrentY = -1f
        var mPreviousX = -1f
        var mPreviousY = -1f

        override fun onTouch(v: View?, event: MotionEvent?): Boolean {
            if (event == null) return false
            when (event.action) {
                MotionEvent.ACTION_DOWN -> {
                    requestUnbufferedDispatch(event)
                    mCurrentX = event.x
                    mCurrentY = event.y
                }
                MotionEvent.ACTION_MOVE -> {
                    mPreviousX = mCurrentX
                    mPreviousY = mCurrentY
                    mCurrentX = event.x
                    mCurrentY = event.y

                    val line = Line(mPreviousX, mPreviousY, mCurrentX, mCurrentY)
                    lines.add(line)
                    renderFrontBufferedLayer()
                }
                MotionEvent.ACTION_CANCEL -> {
                    cancel()
                }
                MotionEvent.ACTION_UP -> {
                    commit()
                }
            }
            return true
        }
    })
}