RecyclerSnapZoom.java

    public void displayShelf(List<String> images, RecyclerView items) {

        //
        Display display = getWindowManager().getDefaultDisplay();
        Point size = new Point();
        display.getSize(size);
        itemWidth = getResources().getDimension(R.dimen.item_width);
        padding = (size.x - itemWidth) / 2;
        firstItemWidth = getResources().getDimension(R.dimen.padding_item_width);
        allPixels = 0;
        //

        final LinearLayoutManager shopItemslayoutManager = new LinearLayoutManager(this);
        shopItemslayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
        items.setLayoutManager(shopItemslayoutManager);
        //items.setSnapEnabled(true, true); // enable zoom and center snap
        items.scrollToPosition(1); // set second element in center

        //
        items.setOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                synchronized (this) {
                    if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                        calculatePositionAndScroll(recyclerView);
                        updateZoom(recyclerView, shopItemslayoutManager);
                    }
                }
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                allPixels += dx;
            }
        });
        //

        ExtraItemsAdapter adapter = new ExtraItemsAdapter(images.size(), images);
        items.setAdapter(adapter);
    }

    //
    private void calculatePositionAndScroll(RecyclerView recyclerView) {
        int expectedPosition = Math.round((allPixels + padding - firstItemWidth) / itemWidth);
        // Special cases for the padding items
        if (expectedPosition == -1) {
            expectedPosition = 0;
        } else if (expectedPosition >= recyclerView.getAdapter().getItemCount() - 2) {
            expectedPosition--;
        }
        scrollListToPosition(recyclerView, expectedPosition);
    }

    private void scrollListToPosition(RecyclerView recyclerView, int expectedPosition) {
        float targetScrollPos = expectedPosition * itemWidth + firstItemWidth - padding;
        float missingPx = targetScrollPos - allPixels;
        if (missingPx != 0) {
            recyclerView.smoothScrollBy((int) missingPx, 0);
        }
    }
    //

    @Override
    protected void onResume() {
        super.onResume();
        final RecyclerView items = (RecyclerView) findViewById(R.id.item_list);

        ViewTreeObserver vto = items.getViewTreeObserver();
        vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                items.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                calculatePositionAndScroll(items);
            }
        });
    }

    public void updateZoom(RecyclerView recycler, LinearLayoutManager lm) {
        int first = lm.findFirstVisibleItemPosition();
        int last = lm.findLastVisibleItemPosition();
        for (int i = first; i < last; i++) {
            View view = lm.findViewByPosition(i);
            int myMidpoint = (view.getRight() - view.getLeft()) / 2;
            int recyclerMidpoint = recycler.getWidth() / 2;

            float scale = Math.abs(myMidpoint - recyclerMidpoint);
            view.setScaleX(scale);
            view.setScaleY(scale);

        }

    }