Android自定义View绘图实现拖影动画

package com.example.disappearinglines;import android.content.Context;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.Path;import android.graphics.PointF;import android.graphics.RectF;import android.os.Handler;import android.os.Message;import android.os.SystemClock;import android.support.annotation.NonNull;import android.util.AttributeSet;import android.util.Log;import android.util.TypedValue;import android.view.MotionEvent;import android.view.View;import java.util.ArrayList;import java.util.Collection;import java.util.Iterator;import java.util.List;import java.util.ListIterator;/** * Created by foruok，欢迎关注我的订阅号“程序视界”. */public class DisappearingDoodleView extends View { public static float convertDipToPx(Context context, float fDip) {  float fPx = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, fDip,    context.getResources().getDisplayMetrics());  return fPx; } final static String TAG = "DoodleView"; class LineElement {  static final public int ALPHA_STEP = 8;  public LineElement(float pathWidth){   mPaint = new Paint();   mPaint.setARGB(255, 255, 0, 0);   mPaint.setAntiAlias(true);   mPaint.setStrokeWidth(0);   mPaint.setStrokeCap(Paint.Cap.BUTT);   mPaint.setStyle(Paint.Style.FILL);   mPath = new Path();   mPathWidth = pathWidth;   for(int i= 0; i < mPoints.length; i++){    mPoints[i] = new PointF();   }  }  public void setPaint(Paint paint){   mPaint = paint;  }  public void setAlpha(int alpha){   mPaint.setAlpha(alpha);   mPathWidth = (alpha * mPathWidth) / 255;  }  private boolean caculatePoints(float k, float b, float x1, float y1, float distance, PointF pt1, PointF pt2){   //point-k formula   // y= kx + b   //distance formula of two points   // distance*distance = Math.pow((x - x1), 2) + Math.pow((y - y1), 2)   // |   // V   // ax*x + bx + c = 0;   // |   // V   // x = (-b +/- Math.sqrt( b*b - 4*a*c ) ) / (2*a)   double a1 = Math.pow(k, 2) + 1;   double b1 = 2* k * (b - y1) - 2 * x1;   double c1 = Math.pow(x1, 2) + Math.pow(b - y1, 2) - Math.pow(distance, 2);   double criterion = Math.pow(b1, 2) - 4*a1*c1;   if(criterion > 0) {    criterion = Math.sqrt(criterion);    pt1.x = (float) ((-b1 + criterion) / (2 * a1));    pt1.y = k * pt1.x + b;    pt2.x = (float) ((-b1 - criterion) / (2 * a1));    pt2.y = k * pt2.x + b;    return true;   }   return false;  }  private void swapPoint(PointF pt1, PointF pt2){   float t = pt1.x;   pt1.x = pt2.x;   pt2.x = t;   t = pt1.y;   pt1.y = pt2.y;   pt2.y = t;  }  public boolean updatePathPoints(){   float distance = mPathWidth / 2;   if(Math.abs(mEndX - mStartX) < 1){    mPoints[0].x = mStartX + distance;    mPoints[0].y = mStartY - distance;    mPoints[1].x = mStartX - distance;    mPoints[1].y = mPoints[0].y;    mPoints[2].x = mPoints[1].x;    mPoints[2].y = mEndY + distance;    mPoints[3].x = mPoints[0].x;    mPoints[3].y = mPoints[2].y;   }else if(Math.abs(mEndY - mStartY) < 1){    mPoints[0].x = mStartX - distance;    mPoints[0].y = mStartY - distance;    mPoints[1].x = mPoints[0].x;    mPoints[1].y = mStartY + distance;    mPoints[2].x = mEndX + distance;    mPoints[2].y = mPoints[1].y;    mPoints[3].x = mPoints[2].x;    mPoints[3].y = mPoints[0].y;   }else{    //point-k formula    //y= kx + b    float kLine = (mEndY - mStartY) / (mEndX - mStartX);    float kVertLine = -1 / kLine;    float b = mStartY - (kVertLine * mStartX);    if(!caculatePoints(kVertLine, b, mStartX, mStartY, distance, mPoints[0], mPoints[1])){     String info = String.format(TAG, "startPt, criterion < 0, (%.2f, %.2f)-->(%.2f, %.2f), kLine - %.2f, kVertLine - %.2f, b - %.2f",       mStartX, mStartY, mEndX, mEndY, kLine, kVertLine, b);     Log.i(TAG, info);     return false;    }    b = mEndY - (kVertLine * mEndX);    if(!caculatePoints(kVertLine, b, mEndX, mEndY, distance, mPoints[2], mPoints[3])){     String info = String.format(TAG, "endPt, criterion < 0, (%.2f, %.2f)-->(%.2f, %.2f), kLine - %.2f, kVertLine - %.2f, b - %.2f",       mStartX, mStartY, mEndX, mEndY, kLine, kVertLine, b);     Log.i(TAG, info);     return false;    }    //reorder points to unti-clockwise    if(mStartX < mEndX){     if(mStartY < mEndY){      if(mPoints[0].x < mPoints[1].x){       swapPoint(mPoints[0], mPoints[1]);      }      if(mPoints[2].x > mPoints[3].x){       swapPoint(mPoints[2], mPoints[3]);      }     }else{      if(mPoints[0].x > mPoints[1].x){       swapPoint(mPoints[0], mPoints[1]);      }      if(mPoints[2].x < mPoints[3].x){       swapPoint(mPoints[2], mPoints[3]);      }     }    }else{     if(mStartY < mEndY){      if(mPoints[0].x < mPoints[1].x){       swapPoint(mPoints[0], mPoints[1]);      }      if(mPoints[2].x > mPoints[3].x){       swapPoint(mPoints[2], mPoints[3]);      }     }else{      if(mPoints[0].x > mPoints[1].x){       swapPoint(mPoints[0], mPoints[1]);      }      if(mPoints[2].x < mPoints[3].x){       swapPoint(mPoints[2], mPoints[3]);      }     }    }   }   return true;  }  // for the first line  public void updatePath(){   //update path   mPath.reset();   mPath.moveTo(mPoints[0].x, mPoints[0].y);   mPath.lineTo(mPoints[1].x, mPoints[1].y);   mPath.lineTo(mPoints[2].x, mPoints[2].y);   mPath.lineTo(mPoints[3].x, mPoints[3].y);   mPath.close();  }  // for middle line  public void updatePathWithStartPoints(PointF pt1, PointF pt2){   mPath.reset();   mPath.moveTo(pt1.x, pt1.y);   mPath.lineTo(pt2.x, pt2.y);   mPath.lineTo(mPoints[2].x, mPoints[2].y);   mPath.lineTo(mPoints[3].x, mPoints[3].y);   mPath.close();  }  public float mStartX = -1;  public float mStartY = -1;  public float mEndX = -1;  public float mEndY = -1;  public Paint mPaint;  public Path mPath;  public PointF[] mPoints = new PointF[4]; //path's vertex  float mPathWidth; } private LineElement mCurrentLine = null; private List<LineElement> mLines = null; private float mLaserX = 0; private float mLaserY = 0; final Paint mPaint = new Paint(); private int mWidth = 0; private int mHeight = 0; private long mElapsed = 0; private float mStrokeWidth = 20; private float mCircleRadius = 10; private Handler mHandler = new Handler(){  @Override  public void handleMessage(Message msg){   DisappearingDoodleView.this.invalidate();  } }; public DisappearingDoodleView(Context context){  super(context);  initialize(context); } public DisappearingDoodleView(Context context, AttributeSet attrs){  super(context, attrs);  initialize(context); } private void initialize(Context context){  mStrokeWidth = convertDipToPx(context, 22);  mCircleRadius = convertDipToPx(context, 10);  mPaint.setARGB(255, 255, 0, 0);  mPaint.setAntiAlias(true);  mPaint.setStrokeWidth(0);  mPaint.setStyle(Paint.Style.FILL); } @Override protected void onSizeChanged (int w, int h, int oldw, int oldh){  mWidth = w;  mHeight = h;  adjustLasterPosition(); } private void adjustLasterPosition(){  if(mLaserX - mCircleRadius < 0) mLaserX = mCircleRadius;  else if(mLaserX + mCircleRadius > mWidth) mLaserX = mWidth - mCircleRadius;  if(mLaserY - mCircleRadius < 0) mLaserY = mCircleRadius;  else if(mLaserY + mCircleRadius > mHeight) mLaserY = mHeight - mCircleRadius; } private void updateLaserPosition(float x, float y){  mLaserX = x;  mLaserY = y;  adjustLasterPosition(); } @Override protected void onDraw(Canvas canvas){  //canvas.drawText("ABCDE", 10, 16, mPaint);  mElapsed = SystemClock.elapsedRealtime();  if(mLines != null) {   updatePaths();   for (LineElement e : mLines) {    if(e.mStartX < 0 || e.mEndY < 0 || e.mPath.isEmpty()) continue;    //canvas.drawLine(e.mStartX, e.mStartY, e.mEndX, e.mEndY, e.mPaint);    canvas.drawPath(e.mPath, e.mPaint);   }   compactPaths();  }  canvas.drawCircle(mLaserX, mLaserY, mCircleRadius, mPaint); } private boolean isValidLine(float x1, float y1, float x2, float y2){  return Math.abs(x1 - x2) > 1 || Math.abs(y1 - y2) > 1; } @Override public boolean onTouchEvent(MotionEvent event){  float x = event.getX();  float y = event.getY();  int action = event.getAction();  if(action == MotionEvent.ACTION_UP){// end one line after finger release   if(isValidLine(mCurrentLine.mStartX, mCurrentLine.mStartY, x, y)){    mCurrentLine.mEndX = x;    mCurrentLine.mEndY = y;    addToPaths(mCurrentLine);   }   //mCurrentLine.updatePathPoints();   mCurrentLine = null;   updateLaserPosition(x, y);   invalidate();   return true;  }  if(action == MotionEvent.ACTION_DOWN){   mLines = null;   mCurrentLine = new LineElement(mStrokeWidth);   mCurrentLine.mStartX = x;   mCurrentLine.mStartY = y;   updateLaserPosition(x, y);   return true;  }  if(action == MotionEvent.ACTION_MOVE) {   if(isValidLine(mCurrentLine.mStartX, mCurrentLine.mStartY, x, y)){    mCurrentLine.mEndX = x;    mCurrentLine.mEndY = y;    addToPaths(mCurrentLine);    mCurrentLine = new LineElement(mStrokeWidth);    mCurrentLine.mStartX = x;    mCurrentLine.mStartY = y;    updateLaserPosition(x, y);   }else{    //do nothing, wait next point   }  }  if(mHandler.hasMessages(1)){   mHandler.removeMessages(1);  }  Message msg = new Message();  msg.what = 1;  mHandler.sendMessageDelayed(msg, 0);  return true; } private void addToPaths(LineElement element){  if(mLines == null) {   mLines = new ArrayList<LineElement>() ;  }  mLines.add(element); } private void updatePaths() {  int size = mLines.size();  if (size == 0) return;  LineElement line = null;  int j = 0;  for (; j < size; j++) {   line = mLines.get(j);   if (line.updatePathPoints()) break;  }  if (j == size) {   mLines.clear();   return;  } else {   for (j--; j >= 0; j--) {    mLines.remove(0);   }  }  line.updatePath();  size = mLines.size();  LineElement lastLine = null;  for (int i = 1; i < size; i++) {   line = mLines.get(i);   if (line.updatePathPoints()){    if (lastLine == null) {     lastLine = mLines.get(i - 1);    }    line.updatePathWithStartPoints(lastLine.mPoints[3], lastLine.mPoints[2]);    lastLine = null;   }else{    mLines.remove(i);    size = mLines.size();   }  } } public void compactPaths(){  int size = mLines.size();  int index = size - 1;  if(size == 0) return;  int baseAlpha = 255 - LineElement.ALPHA_STEP;  int itselfAlpha;  LineElement line;  for(; index >=0 ; index--, baseAlpha -= LineElement.ALPHA_STEP){   line = mLines.get(index);   itselfAlpha = line.mPaint.getAlpha();   if(itselfAlpha == 255){    if(baseAlpha <= 0 || line.mPathWidth < 1){     ++index;     break;    }    line.setAlpha(baseAlpha);   }else{    itselfAlpha -= LineElement.ALPHA_STEP;    if(itselfAlpha <= 0 || line.mPathWidth < 1){     ++index;     break;    }    line.setAlpha(itselfAlpha);   }  }  if(index >= size){   // all sub-path should disappear   mLines = null;  }  else if(index >= 0){   //Log.i(TAG, "compactPaths from " + index + " to " + (size - 1));   mLines = mLines.subList(index, size);  }else{   // no sub-path should disappear  }  long interval = 40 - SystemClock.elapsedRealtime() + mElapsed;  if(interval < 0) interval = 0;  Message msg = new Message();  msg.what = 1;  mHandler.sendMessageDelayed(msg, interval); }}