Android实现bitmap指定区域滑动截取功能

public class ScreenShotView extends View {
  private Dot startDot;
  private Dot endDot;
  private Bitmap mBitmap;
  private Bitmap ocrBitmap;
  private int screenHeight;
  private int screenWidth;
  private Dot leftTopDot;
  private Dot rightBottomDot;
  private Paint paintShadow;
  int shadow = 0xaa000000;
  int clear = 0x0000000;


  public ScreenShotView(Context context) {
    super(context);
    startDot = new Dot();
    endDot = new Dot();
    leftTopDot = new Dot();
    rightBottomDot = new Dot();
  }

  public ScreenShotView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
    startDot = new Dot();
    endDot = new Dot();
    leftTopDot = new Dot();
    rightBottomDot = new Dot();
  }

  public ScreenShotView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    startDot = new Dot();
    endDot = new Dot();
    leftTopDot = new Dot();
    rightBottomDot = new Dot();
  }

  public void setBitmap(Bitmap bitmap, int screenHeight, int screenWidth) {
    mBitmap = bitmap;
    this.screenHeight = screenHeight;
    this.screenWidth = screenWidth;
    changeBitmapSize();
    invalidate();
  }

  public void restart(){
    startDot = new Dot();
    endDot = new Dot();
    leftTopDot = new Dot();
    rightBottomDot = new Dot();
    invalidate();
  }
  /**
  *将将要显示的bitmap进行变形，使其铺满屏幕
  *
  */
  private void changeBitmapSize() {
    int width = mBitmap.getWidth();
    int height = mBitmap.getHeight();
    float scaleWidth = ((float) screenWidth) / width;
    float scaleHeight = ((float) screenHeight) / height;
    Matrix matrix = new Matrix();
    matrix.postScale(scaleWidth, scaleHeight);
    mBitmap = Bitmap.createBitmap(mBitmap, 0, 0, width, height, matrix, true);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    getLeftTopDot();
    getRightBottomDot();
    drawBitmap(canvas);
    drawArea(canvas);
    drawShadowTop(canvas);
    drawShadowLeft(canvas);
    drawShadowRight(canvas);
    drawShadowBottom(canvas);
  }

  /**
  *绘制阴影
  *
  */
  private void drawShadowBottom(Canvas canvas) {
    paintShadow = new Paint();
    paintShadow.setColor(shadow);
    canvas.drawRect(0, rightBottomDot.getY(), screenWidth, screenHeight, paintShadow);
  }

  private void drawShadowRight(Canvas canvas) {
    paintShadow = new Paint();
    paintShadow.setColor(shadow);
    canvas.drawRect(rightBottomDot.getX(), leftTopDot.getY(), screenWidth, rightBottomDot.getY(), paintShadow);
  }

  private void drawShadowLeft(Canvas canvas) {
    paintShadow = new Paint();
    paintShadow.setColor(shadow);
    canvas.drawRect(0, leftTopDot.getY(), leftTopDot.getX(), rightBottomDot.getY(), paintShadow);
  }

  private void drawShadowTop(Canvas canvas) {
    paintShadow = new Paint();
    paintShadow.setColor(shadow);
    canvas.drawRect(0, 0, screenWidth, leftTopDot.getY(), paintShadow);
  }

  private void drawBitmap(Canvas canvas) {
    Paint paint = new Paint();
    canvas.drawBitmap(mBitmap, 0, 0, paint);
  }

  /**
   * 画出截图区域
   *
   * @param canvas
   */
  private void drawArea(Canvas canvas) {
    Paint paint = new Paint();
    paint.setColor(clear);
    canvas.drawRect(leftTopDot.getX(), leftTopDot.getY(), rightBottomDot.getX(), rightBottomDot.getY(), paint);
  }


  /**
   * 获取截图区域bitmap
   *
   * @return 截图
   */
  public Bitmap getBitmap() {
    if (mBitmap != null) {
      getLeftTopDot();
      getRightBottomDot();
      if (getBitmapOutWidth() > 0 && getBitmapOutHeight() > 0) {
        if(leftTopDot.getY()<0){
          leftTopDot.setY(0);
        }
        ocrBitmap = Bitmap.createBitmap(mBitmap, (int) leftTopDot.getX(), (int) leftTopDot.getY(), getBitmapOutWidth(), getBitmapOutHeight());
      }
    }
    return ocrBitmap;
  }

  /**
   * 获取截图区域宽度
   *
   * @return
   */
  private int getOutWidth() {
    return (int) (rightBottomDot.getX() - leftTopDot.getX());
  }

  /**
   * 获取截图区域高度
   *
   * @return
   */
  private int getOutHeight() {
    return (int) (rightBottomDot.getY() - leftTopDot.getY());
  }

  private int getBitmapOutWidth() {
    int bitmapOutWidth;
    int scale = getOutWidth() * mBitmap.getWidth();
    bitmapOutWidth = scale / screenWidth;
    return bitmapOutWidth;
  }

  private int getBitmapOutHeight() {
    int bitmapOutHeight;
    int scale = getOutHeight() * mBitmap.getHeight();
    bitmapOutHeight = scale / screenHeight;
    return bitmapOutHeight;
  }

  private void getLeftTopDot() {
    if (endDot.getX() > startDot.getX()) {
      leftTopDot.setX(startDot.getX());
    } else {
      leftTopDot.setX(endDot.getX());
    }
    if (endDot.getY() > startDot.getY()) {
      leftTopDot.setY(startDot.getY());
    } else {
      leftTopDot.setY(endDot.getY());
    }
  }

  private void getRightBottomDot() {
    if (startDot.getX() > endDot.getX()) {
      rightBottomDot.setX(startDot.getX());
    } else {
      rightBottomDot.setX(endDot.getX());
    }
    if (startDot.getY() > endDot.getY()) {
      rightBottomDot.setY(startDot.getY());
    } else {
      rightBottomDot.setY(endDot.getY());
    }

  }

  public Dot getStartDot() {
    return startDot;
  }

  public void setStartDot(Dot startDot) {
    this.startDot = startDot;
  }

  public Dot getEndDot() {
    return endDot;
  }

  public void setEndDot(Dot endDot) {
    this.endDot = endDot;
  }

}

public class MainActivity extends AppCompatActivity implements View.OnTouchListener, View.OnClickListener {
  private ScreenShotView screenShotView;
  private Bitmap bmp;
  private Bitmap ocrBitmap;
  private TextView certainBtn;
  private TextView cancelBtn;
  private TextView restartBtn;
  private int screenWidth;
  private int screenHeight;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    screenShotView = (ScreenShotView) findViewById(R.id.screenShotView);
    cancelBtn = (TextView) findViewById(R.id.cancel_btn);
    cancelBtn.setOnClickListener(this);
    certainBtn = (TextView) findViewById(R.id.certain_btn);
    certainBtn.setOnClickListener(this);
    restartBtn = (TextView)findViewById(R.id.restart_btn);
    restartBtn.setOnClickListener(this);
    DisplayMetrics dm = new DisplayMetrics();
    //获取屏幕信息
    getWindowManager().getDefaultDisplay().getMetrics(dm);
    screenWidth = dm.widthPixels;
    screenHeight = dm.heightPixels;
    Resources r = this.getResources();
    InputStream is = r.openRawResource(R.raw.bg);
    BitmapDrawable bmpDraw = new BitmapDrawable(is);
    bmp = bmpDraw.getBitmap();
    screenShotView.setBitmap(bmp, screenHeight, screenWidth);
    screenShotView.setOnTouchListener(this);
  }

  @Override
  public boolean onTouch(View view, MotionEvent motionEvent) {
    switch (motionEvent.getAction()) {
      case MotionEvent.ACTION_DOWN:
        screenShotView.setStartDot(new Dot(motionEvent.getX(), motionEvent.getY()));
        break;
      case MotionEvent.ACTION_MOVE:
        screenShotView.setEndDot(new Dot(motionEvent.getX(), motionEvent.getY()));
        screenShotView.setBitmap(bmp, screenHeight, screenWidth);
        break;
      case MotionEvent.ACTION_UP:
        ocrBitmap = screenShotView.getBitmap();
        break;
    }
    return true;
  }

  @Override
  public void onClick(View view) {
    switch (view.getId()) {
      case R.id.cancel_btn:
        finish();
        break;
      case R.id.certain_btn:
        if (ocrBitmap != null) {
          BitmapUtil.getInstance().setImageBitmap(ocrBitmap);
          Intent intent = new Intent(MainActivity.this, Main2Activity.class);
          startActivity(intent);
        }else{
          Toast.makeText(MainActivity.this,"请选择截取区域",Toast.LENGTH_SHORT).show();
        }
        break;
      case R.id.restart_btn:
        screenShotView.restart();
        break;
    }
  }

  @Override
  protected void onResume() {
    super.onResume();
    screenShotView.restart();
  }

  @Override
  protected void onRestart() {
    super.onRestart();
    screenShotView.restart();
  }
}