How do you scale an ImageView like centerCrop, but from top?

Question

Let's say I'm getting some image from an API. I have no idea what the image's dimensions will be ahead of time, but I know that I want that image to become the src of an ImageView I have set to some specific size. I want whatever image I get from the API to fill the entire ImageView, I want to preserve aspect ratio, and I don't care if one dimension (width or height) becomes too big for the set size of the view—so I use centerCrop.

<ImageView
  android:layout_width="400px"
  android:layout_height="300px"
  android:scaleType="centerCrop" />

If the image that comes back from the API is this:

When it gets set as the ImageView's src, the result will be something akin to this (shaded parts are cropped off):

However, I get a request that we should always show the top of the image and crop from the bottom up. So the desired result is something like this:

I'm sure this is possible, but I'm a web guy operating out of his league here. Will it be better to extend ImageView somehow, or to try scaleType="matrix" and setImageMatrix(), or some third, unmentioned option?

Answer 1

Use this TopCropImageView gist

import android.content.Context;
import android.graphics.Matrix;
import android.widget.ImageView;

/**
* ImageView to display top-crop scale of an image view.
*
* @author Chris Arriola
*/
public class TopCropImageView extends ImageView {

    public TopCropImageView(Context context) {
        super(context);
        setScaleType(ScaleType.MATRIX);
    }

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

    @Override
    protected boolean setFrame(int l, int t, int r, int b) {
        recomputeImgMatrix();
        return super.setFrame(l, t, r, b);
    }      

    private void recomputeImgMatrix() {
        final Matrix matrix = getImageMatrix();

        float scale;
        final int viewWidth = getWidth() - getPaddingLeft() - getPaddingRight();
        final int viewHeight = getHeight() - getPaddingTop() - getPaddingBottom();
        final int drawableWidth = getDrawable().getIntrinsicWidth();
        final int drawableHeight = getDrawable().getIntrinsicHeight();

        if (drawableWidth * viewHeight > drawableHeight * viewWidth) {
            scale = (float) viewHeight / (float) drawableHeight;
        } else {
            scale = (float) viewWidth / (float) drawableWidth;
        }

        matrix.setScale(scale, scale);
        setImageMatrix(matrix);
    }
}