java - onDraw优化，如何提高性能？

Question

我正在尝试在 .png 图像上绘图，但速度非常慢。如果我在没有 .png 文件的 imageView 上绘图，它可以正常工作。我该如何解决这个问题？据我所知，我需要防止“一直有很多图画”，我怎样才能实现这一点？

代码:

public class Draw
    extends Activity{

DrawingView dv ;
private Paint       mPaint;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dv = new DrawingView(this);
    setContentView(dv);
    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setDither(true);
    mPaint.setColor(Color.GREEN);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(12);
}

public class DrawingView extends View {

    public int width;
    public  int height;
    private Bitmap  mBitmap;
    private Canvas  mCanvas;
    private Path    mPath;
    private Paint   mBitmapPaint;
    Context context;
    private Paint circlePaint;
    private Path circlePath;

    public DrawingView(Context c) {
        super(c);
        context=c;
        mPath = new Path();
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        circlePaint = new Paint();
        circlePath = new Path();
        circlePaint.setAntiAlias(true);
        circlePaint.setColor(Color.BLUE);
        circlePaint.setStyle(Paint.Style.STROKE);
        circlePaint.setStrokeJoin(Paint.Join.MITER);
        circlePaint.setStrokeWidth(4f);


    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);

    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Bitmap bm = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory() + "/MANUAL/workflow" + "/img.png");
        int targetWidth  = bm.getWidth() / 1;
        int targetHeight = bm.getHeight() / 1;
        Matrix matrix = new Matrix();
        matrix.postScale(0.7f, 0.65f);
        Bitmap size = Bitmap.createBitmap(bm, 0, 0, targetWidth, targetHeight, matrix, true);
        Paint paint = new Paint();
        paint.setColor(Color.RED);
        canvas.drawBitmap(size, 0, 0, paint);

        canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);
        canvas.drawPath( mPath,  mPaint);
        canvas.drawPath( circlePath,  circlePaint);
    }

    private float mX, mY;
    private static final float TOUCH_TOLERANCE = 4;

    private void touch_start(float x, float y) {
        mPath.reset();
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
    }
    private void touch_move(float x, float y) {
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y - mY);
        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
            mX = x;
            mY = y;

            circlePath.reset();
            circlePath.addCircle(mX, mY, 30, Path.Direction.CW);
        }
    }
    private void touch_up() {
        mPath.lineTo(mX, mY);
        circlePath.reset();
        // commit the path to our offscreen
        mCanvas.drawPath(mPath,  mPaint);
        // kill this so we don't double draw
        mPath.reset();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touch_start(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
        }
        return true;
    }
}

Answer 1

您的 onDraw() 方法应如下所示:

@Override
protected void onDraw(Canvas canvas) {

    paint.setColor(Color.RED);
    canvas.drawBitmap(size, 0, 0, paint);
    canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);
    canvas.drawPath( mPath,  mPaint);
    canvas.drawPath( circlePath,  circlePaint);
}

所有位图解码和调整大小都应该在外部完成(在构造函数中或仅在调整 View 大小时)，无需每次都进行解码和调整大小，因为每次结果都相同。