Android Canvas如何缩放位图但保持原始绑定？

Question

I want to scale a Bitmap using Canvas

I need to keep the Bitmap original width and height

and the scaled one aligns center-middle in bound

here is what I have tried:

public Bitmap scale(Bitmap src) {
    int width = src.getWidth();
    int height = src.getHeight();
    float scaledWidth = width * .5f;
    float scaledHeight = height * .5f;

    Bitmap transBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(transBitmap);
    Paint paint = new Paint();
    float dx = (width - scaledWidth);
    float dy = (height - scaledHeight);
    canvas.drawBitmap(src, null, new RectF(dx, dy, scaledWidth, scaledHeight), paint);

    Matrix m = new Matrix();
    m.setRectToRect(new RectF(0, 0, src.getWidth(), src.getHeight()), new RectF(0, 0, scaledWidth, scaledHeight), Matrix.ScaleToFit.CENTER);
    Bitmap output = Bitmap.createBitmap(src, 0, 0, src.getWidth(), src.getHeight(), m, true);

    //return transBitmap;
    return output;
}

I used this method in custom ImageView onTouch:

 switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            setImageBitmap(scaledBmp);
            break;
        case MotionEvent.ACTION_UP:
            setImageDrawable(originalDrawable);
            break;
    }

UPDATE

MyImageView.java

public class MyImageView extends ImageView {

    private Drawable mDrawable;
    private Drawable mScaled;

    public MyImageView(Context context, Drawable drawable) {
        super(context);
        setImageDrawable(drawable);
        Bitmap src = ((BitmapDrawable) drawable).getBitmap();
        mDrawable = drawable;
        mScaled = new BitmapDrawable(getResources(), makeScaled(src));
    }

    public Bitmap makeScaled(Bitmap src) {
        int width = src.getWidth();
        int height = src.getHeight();
        float scaledWidth = width * .95f;
        float scaledHeight = height * .95f;
        Matrix m = new Matrix();
        m.setRectToRect(new RectF(0, 0, src.getWidth(), src.getHeight()), new RectF(0, 0, scaledWidth, scaledHeight), Matrix.ScaleToFit.CENTER);
        Bitmap output = Bitmap.createBitmap(src, 0, 0, src.getWidth(), src.getHeight(), m, true);
        Canvas xfas = new Canvas(output);
        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setFilterBitmap(true);
        paint.setDither(true);
        xfas.drawBitmap(output, 0, 0, paint);

        return output;
    }

    @Override public boolean dispatchTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                setImageDrawable(mScaled);
                break;
            case MotionEvent.ACTION_UP:
                setImageDrawable(mDrawable);
                break;
        }
        return super.dispatchTouchEvent(event);
    }

}

Answer 1

If I have not misunderstood, one solution is to use a Matrix and its setRectToRect to translate the original values to the desired one. From the documentation

Set the matrix to the scale and translate values that map the source rectangle to the destination rectangle, returning true if the the result can be represented.

Matrix m = new Matrix();
m.setRectToRect(new RectF(0, 0, src.getWidth(), src.getHeight()), new RectF(0, 0, scaledWidth, scaledHeigth), Matrix.ScaleToFit.CENTER);
Bitmap output = Bitmap.createBitmap(src, 0, 0, src.getWidth(), src.getHeight(), m, true);

and then simply draw the scaled bitmap on your canvas

Answer 2

Solved

public static Bitmap scaleBitmap(Bitmap src, float factor) {
    int width = src.getWidth();
    int height = src.getHeight();
    int scaledWidth = (int) (width * factor);
    int scaledHeight = (int) (height * factor);
    Bitmap bmp = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    Bitmap scaled = Bitmap.createScaledBitmap(src, scaledWidth, scaledHeight, false);
    Canvas canvas = new Canvas(bmp);
    Paint paint = new Paint();
    int distX = (width - scaledWidth) / 2;
    int distY = (height - scaledHeight) / 2;
    canvas.drawBitmap(scaled, distX, distY, paint);
    return bmp;
}