Android粒子线条效果实现过程与代码

import android.annotation.SuppressLint
import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Paint
import android.os.Handler
import android.os.Looper
import android.os.Message
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import java.lang.ref.WeakReference
import kotlin.math.pow
import kotlin.math.sqrt

class ParticleLinesBgView @JvmOverloads constructor(
    context: Context,
    attributeSet: AttributeSet? = null,
    defStyleAttr: Int = 0
): View(context, attributeSet, defStyleAttr){
    companion object{
        // 屏幕刷新时间，每秒20次
        const val SCREEN_FLUSH_TIME = 50L
        // 新增点的间隔时间
        const val POINT_ADD_TIME = 200L
        // 粒子存活时间
        const val POINT_ALIVE_TIME = 18000L
        // 吸引的合适距离
        const val ATTRACT_LENGTH = 250f
        // 维持的合适距离
        const val PROPER_LENGTH = 150f
        // 粒子被吸引每次接近的距离
        const val POINT_MOVE_LENGTH = 30f
        // 距离计算公式
        fun getDistance(x1: Float, y1: Float, x2: Float, y2: Float): Float {
            return sqrt(((x1 - x2).toDouble().pow(2.0)
                    + (y1 - y2).toDouble().pow(2.0)).toFloat())
        }
    }
    // 存放的粒子
    private val mParticles = ArrayList<Particle>(64)
    // 手指按下位置
    private var mTouchParticle: Particle? = null
    // 处理的handler
    private val mHandler = ParticleHandler(this)
    // 画笔
    private val mPaint = Paint().apply {
        color = Color.LTGRAY
        strokeWidth = 3f
        style = Paint.Style.STROKE
        flags = Paint.ANTI_ALIAS_FLAG
    }
    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(w, h, oldw, oldh)
        // 通过发送消息给handler实现间隔添加点
        mHandler.removeMessages(0)
        mHandler.sendEmptyMessageDelayed(0, POINT_ADD_TIME)
    }
    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        // 绘制点和线
        for (i in 0 until mParticles.size) {
            val point = mParticles[i]
            canvas.drawPoint(point.x, point.y, mPaint)
            // 连线
            for (j in (i + 1) until mParticles.size) {
                val another = mParticles[j]
                val distance = getDistance(point.x, point.y, another.x, another.y)
                if (distance <= PROPER_LENGTH) {
                    canvas.drawLine(point.x, point.y, another.x, another.y, mPaint)
                }
            }
        }
        mTouchParticle?.let {
            // 手指按下点与附近连线
            for(point in mParticles) {
                val distance = getDistance(point.x, point.y, it.x, it.y)
                if (distance <= PROPER_LENGTH) {
                    canvas.drawLine(point.x, point.y, it.x, it.y, mPaint)
                }
            }
            // 吸引范围显示
            mPaint.color = Color.BLUE
            canvas.drawCircle(it.x, it.y, PROPER_LENGTH, mPaint)
            mPaint.color = Color.LTGRAY
        }
    }
    @SuppressLint("ClickableViewAccessibility")
    override fun onTouchEvent(event: MotionEvent): Boolean {
        when(event.action) {
            MotionEvent.ACTION_DOWN -> {
                mTouchParticle = Particle(event.x, event.y, 0)
            }
            MotionEvent.ACTION_MOVE -> {
                mTouchParticle!!.x = event.x
                mTouchParticle!!.y = event.y
                invalidate()
            }
            MotionEvent.ACTION_UP -> {
                mTouchParticle = null
            }
        }
        return true
    }
    // 粒子
    class Particle(var x: Float, var y: Float, var counter: Int)
    // kotlin自动编译为Java静态类，控件引用使用弱引用
    class ParticleHandler(view: ParticleLinesBgView): Handler(Looper.getMainLooper()){
        // 控件引用
        private val mRef: WeakReference<ParticleLinesBgView> = WeakReference(view)
        // 粒子出现控制
        private var mPointCounter = 0
        override fun handleMessage(msg: Message) {
            mRef.get()?.let {view->
                // 新增点
                mPointCounter++
                if (mPointCounter == (POINT_ADD_TIME / SCREEN_FLUSH_TIME).toInt()) {
                    // 随机位置
                    val x = (Math.random() * view.width).toFloat()
                    val y = (Math.random() * view.height).toFloat()
                    view.mParticles.add(Particle(x, y, 0))
                    mPointCounter = 0
                }
                val iterator = view.mParticles.iterator()
                while (iterator.hasNext()) {
                    val point = iterator.next()
                    // 移除失活粒子
                    if (point.counter == (POINT_ALIVE_TIME / SCREEN_FLUSH_TIME).toInt()) {
                        iterator.remove()
                    }
                    // 手指按下时，粒子朝合适的距离移动
                    view.mTouchParticle?.let {
                        val distance = getDistance(point.x, point.y, it.x, it.y)
                        if(distance in PROPER_LENGTH..ATTRACT_LENGTH) {
                            // 横向接近
                            if (point.x < it.x) point.x += POINT_MOVE_LENGTH
                            else point.x -= POINT_MOVE_LENGTH
                            // 纵向接近
                            if (point.y < it.y) point.y += POINT_MOVE_LENGTH
                            else point.y -= POINT_MOVE_LENGTH
                        }else if(distance <= PROPER_LENGTH) {
                            // 横向远离
                            if (point.x < it.x) point.x -= POINT_MOVE_LENGTH
                            else point.x += POINT_MOVE_LENGTH
                            // 纵向远离
                            if (point.y < it.y) point.y -= POINT_MOVE_LENGTH
                            else point.y += POINT_MOVE_LENGTH
                        }
                    }
                }
                // 循环发送
                view.invalidate()
                view.mHandler.sendEmptyMessageDelayed(0, POINT_ADD_TIME)
            }
        }
    }
}