Android Custom View に BitMap を描画

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package org.sibainu.relax.room.scalegesturedetector;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;

import androidx.annotation.Nullable;

public class GestureView extends View {

    private Context context;
    //表示するビットマップ画像
    private Bitmap _bm;
    //ピンチ操作開始のX座標
    private float _focusx;
    //ピンチ操作開始のY座標
    private float _focusy;
    //ピンチ操作時の画像の縮尺
    private float _lastscalefactor = 1.0f;
    //デフォルトの画像の縮尺
    private float firstrate = 1.0f;
    //描画の左上のx座標
    private float firstx =0.0f;
    //描画の左上のy座標
    private float firsty =0.0f;
    //View自身の横幅
    private int viewwidth;
    //View自身の高さ
    private int viewheight;

    //画像の描画を設定するオブジェクト
    private Matrix drawmatrix = new Matrix();
    //Paintオブジェクト
    private Paint paint = new Paint();

    //ピンチ操作時の動き感知するリスナーの作成
    private ScaleGestureDetector scalegesturedetector;
    private ScaleGestureDetector.SimpleOnScaleGestureListener scalegesturelistener =
            new ScaleGestureDetector.SimpleOnScaleGestureListener() {
        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            Log.d("scale","onscalebegin");
            //ピンチ操作開始
            //開始座標を取得
            _focusx = detector.getFocusX();
            _focusy = detector.getFocusY();
            return super.onScaleBegin(detector);
        }

        @Override
        public void onScaleEnd(ScaleGestureDetector detector) {
            //ピンチ操作終了
            super.onScaleEnd(detector);
        }

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            //ピンチ操作中
            //縮尺率を取得
            _lastscalefactor = detector.getScaleFactor();
            //縦横の拡大縮小を設定するマトリックスの作成
            drawmatrix.postScale(_lastscalefactor,
                                 _lastscalefactor,
                                 _focusx,
                                 _focusy);
            //これを実行することにより onDraw が発火
            invalidate();
            super.onScale(detector);
            return true;
        }
    };

    //2本指スクロールの動き感知するリスナーの作成
    private GestureDetector gesturedetector;
    private GestureDetector.SimpleOnGestureListener gesturelistener =
            new GestureDetector.SimpleOnGestureListener() {
        @Override
        public boolean onScroll (MotionEvent e1,
                                 MotionEvent e2,
                                 float distanceX,
                                 float distanceY) {
            Log.d("scroll","onscroll");
            // スクロールしたとき
            if (e1.getPointerId(0) ==
                    e2.getPointerId(0)) {
                // 画像を移動
                drawmatrix.postTranslate(-distanceX, -distanceY);
                //これを実行することにより onDraw が発火
                invalidate();
            }
            return super.onScroll(e1, e2, distanceX, distanceY);
        }

        @Override
        public boolean onDoubleTap (MotionEvent e) {
            Log.d("doubletap","onDoubleTap");
            drawmatrix.reset();
            //drawmatrix.postScale(firstrate, firstrate, firstx, firsty);
            drawmatrix.postScale(firstrate, firstrate);
            drawmatrix.postTranslate(firstx, firsty);
            invalidate();
            return super.onDoubleTap(e);
        }
    };

    // コンストラクタ
    public GestureView (Context context) {
        super(context);
        this.context = context;
        init();
    }

    public GestureView (Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context = context;
        init();
    }

    public GestureView (Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.context = context;
        init();
    }

    private void init () {
        //リスナーを組み込む
        scalegesturedetector = new ScaleGestureDetector(context, scalegesturelistener);
        gesturedetector = new GestureDetector(context, gesturelistener);
    }

    @Override
    public boolean onTouchEvent (MotionEvent event) {
        super.onTouchEvent(event);
        // すべてのGestureはここを通る
        Log.d("touchevent",String.valueOf(gesturedetector.onTouchEvent(event)));
        return scalegesturedetector.onTouchEvent(event) ||
               gesturedetector.onTouchEvent(event) ||
               super.onTouchEvent(event);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        //再描画時の累積した Matrix drawmatrix を適応
        canvas.save();
        canvas.drawBitmap(_bm, drawmatrix, paint);
        canvas.restore();
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);

        // BitMap の全体表示をデフォルトとする drawmatirix を作成します
        viewwidth = getWidth();   // Viewの横幅を取得
        viewheight = getHeight(); // Viewの高さを取得

        int bmwidth = _bm.getWidth();
        float widthrate = viewwidth * 1.0f / bmwidth;
        if (firstrate > widthrate) {
            firstrate = widthrate;
        }

        int bmheight = _bm.getHeight();
        float heightrate = viewheight * 1.0f / bmheight;
        if (firstrate > heightrate) {
            firstrate = heightrate;
        }
        if (firstrate != 1.0f) {
            //キャンバスの中心に描画します
            firstx = (viewwidth - bmwidth * firstrate) / 2;
            firsty = (viewheight - bmheight * firstrate) / 2;
            //相似の拡大縮小・移動 sx:firstrate  sy:firstrate  px:firstx  py:firsty
            //drawmatrix.postScale(firstrate, firstrate, firstx, firsty);
            drawmatrix.postScale(firstrate, firstrate);
            drawmatrix.postTranslate(firstx, firsty);
        }
    }

    public void setImageBitmap(Bitmap bm) {
        _bm = bm;
        invalidate();
    }
}