Android畫板開(kāi)發(fā)之橡皮擦功能

companion object {
  const val EDIT_MODE_PEN = 0x1L  //畫筆模式
  const val EDIT_MODE_ERASER = 0x2L //橡皮擦模式
 }

 @Retention(AnnotationRetention.SOURCE)
 @IntDef(EDIT_MODE_PEN, EDIT_MODE_ERASER)
 annotation class EditMode

 //當(dāng)前編輯模式默認(rèn)為畫筆模式
 @EditMode
 private var mMode: Long = EDIT_MODE_PEN

 /**
  * 設(shè)置畫筆模式
  */
 fun setModel(@EditMode model:Long){
  mMode = model
  when(model){
   EDIT_MODE_PEN -> {
    //畫線
    mPaint.xfermode = null
   }
   EDIT_MODE_ERASER ->{
    mPaint.xfermode = PorterDuffXfermode(PorterDuff.Mode.CLEAR)

   }
  }
 }

//想要繪制的內(nèi)容先繪制到這個(gè)增加的canvas對(duì)應(yīng)的bitmap上，
// 寫完后再把這個(gè)bitmap的ARGB信息一次提交給上下文的canvas去繪制
 private lateinit var mBufferBitmap: Bitmap
 private lateinit var mBufferCanvas: Canvas

override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
 super.onMeasure(widthMeasureSpec, heightMeasureSpec)
 if(mBufferCanvas == null){
   mBufferBitmap = Bitmap.createBitmap(measuredWidth, measuredHeight, Bitmap.Config.ARGB_8888)

   //canvas繪制的內(nèi)容，將會(huì)在這個(gè)mBufferBitmap內(nèi)
   mBufferCanvas = Canvas(mBufferBitmap)
  }

}

MotionEvent.ACTION_MOVE -> { //手指移動(dòng)的時(shí)候
  //繪制圓滑曲線，即貝塞爾曲線,貝塞爾曲線這個(gè)知識(shí)自行了解
  mPath.quadTo(preX,preY,event.x,event.y)

  //在緩存里面繪制
  mBufferCanvas.drawPath(mPath,mPaint)

  //重新繪制，會(huì)調(diào)用onDraw方法
  invalidate()
  preX = event.x
  preY = event.y
}

override fun onDraw(canvas: Canvas) {
  super.onDraw(canvas)
  //畫出緩存bitmap的內(nèi)容
  canvas.drawBitmap(mBufferBitmap,0f,0f,null)

 }

class TPEraserView(context: Context, attr: AttributeSet) : View(context,attr) {

 companion object {
  const val EDIT_MODE_PEN = 0x1L  //畫筆模式
  const val EDIT_MODE_ERASER = 0x2L //橡皮擦模式
 }

 @Retention(AnnotationRetention.SOURCE)
 @IntDef(EDIT_MODE_PEN, EDIT_MODE_ERASER)
 annotation class EditMode

 //當(dāng)前編輯模式默認(rèn)為畫筆模式
 @EditMode
 private var mMode: Long = EDIT_MODE_PEN

 private var preX: Float = 0.0f //上一次的觸摸點(diǎn)x坐標(biāo)
 private var preY: Float = 0.0f //上一次觸摸點(diǎn)y坐標(biāo)

 private var mPath = Path() //path路徑
 //畫筆
 private var mPaint = Paint(Paint.ANTI_ALIAS_FLAG or Paint.DITHER_FLAG)

 //想要繪制的內(nèi)容先繪制到這個(gè)增加的canvas對(duì)應(yīng)的bitmap上，
 // 寫完后再把這個(gè)bitmap的ARGB信息一次提交給上下文的canvas去繪制
 private lateinit var mBufferBitmap: Bitmap
 private lateinit var mBufferCanvas: Canvas


 init {
  mPaint.style = Paint.Style.STROKE //畫筆為實(shí)心
  mPaint.color = Color.RED   //顏色
  mPaint.strokeCap = Paint.Cap.ROUND //筆觸為圓形
  mPaint.strokeWidth = 10f   //畫筆大小
 }

 override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int){
  super.onMeasure(widthMeasureSpec, heightMeasureSpec)
  mBufferBitmap = Bitmap.createBitmap(measuredWidth, measuredHeight, Bitmap.Config.ARGB_8888)

  //canvas繪制的內(nèi)容，將會(huì)在這個(gè)mBufferBitmap內(nèi)
  mBufferCanvas = Canvas(mBufferBitmap)

 }

 override fun onDraw(canvas: Canvas) {
  super.onDraw(canvas)
  //畫出緩存bitmap的內(nèi)容
  canvas.drawBitmap(mBufferBitmap,0f,0f,null)

 }

 override fun onTouchEvent(event: MotionEvent): Boolean {

  when(event.action){
   MotionEvent.ACTION_DOWN -> { //手指按下的時(shí)候
    //將起始點(diǎn)移動(dòng)到當(dāng)前坐標(biāo)
    mPath.moveTo(event.x,event.y)

    //記錄上次觸摸的坐標(biāo)，注意ACTION_DOWN方法只會(huì)執(zhí)行一次
    preX = event.x
    preY = event.y
   }
   MotionEvent.ACTION_MOVE -> { //手指移動(dòng)的時(shí)候
    //繪制圓滑曲線，即貝塞爾曲線,貝塞爾曲線這個(gè)知識(shí)自行了解
    mPath.quadTo(preX,preY,event.x,event.y)

    //在緩存里面繪制
    mBufferCanvas.drawPath(mPath,mPaint)

    //重新繪制，會(huì)調(diào)用onDraw方法
    invalidate()
    preX = event.x
    preY = event.y
   }
   MotionEvent.ACTION_UP ->{
    //清除路徑的內(nèi)容
    mPath.reset()
   }
  }

  // true：告訴系統(tǒng)，這個(gè)觸摸事件由我來(lái)處理
  // false：告訴系統(tǒng)，這個(gè)觸摸事件我不處理，這時(shí)系統(tǒng)會(huì)把觸摸事件傳遞給imageview的父節(jié)點(diǎn)
  return true
 }

 /**
  * 設(shè)置畫筆模式
  */
 fun setModel(@EditMode model:Long){
  mMode = model
  when(model){
   EDIT_MODE_PEN -> {
    mPaint.xfermode = null
   }
   EDIT_MODE_ERASER ->{
    mPaint.xfermode = PorterDuffXfermode(PorterDuff.Mode.CLEAR)

   }
  }
 }

}

 /**
  * 清空畫布
  */
 fun clear() {
  mBufferCanvas.drawColor(0, PorterDuff.Mode.CLEAR)
  invalidate()
 }