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| package com.google.androidtutorial | |
| import android.content.Context | |
| import android.graphics.Canvas | |
| import android.graphics.Color | |
| import android.graphics.Paint | |
| import android.util.AttributeSet | |
| import android.view.SurfaceHolder | |
| import android.view.SurfaceView | |
| import kotlinx.coroutines.* | |
| import kotlin.random.Random | |
| class MySurfaceView(context: Context, attrs: AttributeSet?, defStyleAttr: Int) | |
| : SurfaceView(context, attrs, defStyleAttr), SurfaceHolder.Callback { | |
| constructor(context: Context): this(context, null, 0) | |
| constructor(context: Context, attrs: AttributeSet): this(context, attrs, 0) | |
| private var drawingJob: Job? = null | |
| init { | |
| holder.addCallback(this) | |
| } | |
| override fun surfaceChanged(holder: SurfaceHolder, format: Int, width: Int, height: Int) { } | |
| override fun surfaceDestroyed(holder: SurfaceHolder) { | |
| runBlocking { | |
| drawingJob?.cancelAndJoin() | |
| } | |
| } | |
| override fun surfaceCreated(holder: SurfaceHolder) { | |
| drawingJob = GlobalScope.launch { | |
| // While this coroutine is running | |
| while(isActive) { | |
| // canvas for double buffering | |
| val canvas = holder.lockCanvas()?: continue | |
| try { | |
| synchronized(holder) { | |
| // drawing logic | |
| drawingLogic(canvas) | |
| } | |
| } finally { | |
| // print to screen | |
| holder.unlockCanvasAndPost(canvas) | |
| } | |
| } | |
| } | |
| } | |
| private val raindrops = mutableListOf<Pair<Int, Long>>() | |
| // add new raindrop to the list | |
| private fun newRainDrop(width: Int, time: Long) { | |
| val x = Random.nextInt(width+1) | |
| raindrops.add(x to time) | |
| } | |
| // maximum number of raindrops that can be generated at the same time | |
| private val maximumNewRaindrops = 5 | |
| private val raindropSpeed = 500 | |
| private val tailLength = 20 | |
| private fun drawingLogic(canvas: Canvas) { | |
| // clear canvas | |
| canvas.drawColor(Color.DKGRAY) | |
| val time = System.currentTimeMillis() | |
| // generate raindrops | |
| repeat(Random.nextInt(maximumNewRaindrops + 1)) { | |
| newRainDrop(canvas.width, time) | |
| } | |
| // color of the raindrops | |
| val p = Paint() | |
| p.color = Color.WHITE | |
| // draw raindrops | |
| val terminatingDrops = mutableListOf<Pair<Int, Long>>() | |
| raindrops.forEach { drop -> | |
| // calculate position | |
| val x = drop.first.toFloat() | |
| val y = ((time - drop.second) / 1000f * raindropSpeed) | |
| if(y > canvas.height) { | |
| // drops out of the screen | |
| terminatingDrops.add(drop) | |
| } else { | |
| canvas.drawRect(x, y-tailLength, x+1, y, p) | |
| } | |
| } | |
| // remove drops out of the screen | |
| raindrops.removeAll(terminatingDrops) | |
| } | |
| } |
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