Why Should I call setTranslationX() in transformPage() , doesnt it effect the final postion of the View?

Question

I'm having trouble understanding the usage of transformPage() method in PageTransformer class.

Take the Official ZoomOut Transformer as an example:

public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();
        int pageHeight = view.getHeight();

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.
            view.setAlpha(0);

        } else if (position <= 1) { // [-1,1]
            // Modify the default slide transition to shrink the page as well
            float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
            float vertMargin = pageHeight * (1 - scaleFactor) / 2;
            float horzMargin = pageWidth * (1 - scaleFactor) / 2;
            if (position < 0) {
                view.setTranslationX(horzMargin - vertMargin / 2);
            } else {
                view.setTranslationX(-horzMargin + vertMargin / 2);
            }

            // Scale the page down (between MIN_SCALE and 1)
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);

            // Fade the page relative to its size.
            view.setAlpha(MIN_ALPHA +
                    (scaleFactor - MIN_SCALE) /
                    (1 - MIN_SCALE) * (1 - MIN_ALPHA));

        } else { // (1,+Infinity]
            // This page is way off-screen to the right.
            view.setAlpha(0);
        }
    }

I understand we need to consider two views, one is on left(-1--0) and the other on right hand side(0--1)

but i dont understand the view.setTranslationX() usage, seems like even if i delete those lines of code, the difference is just the gap between the two views when swiping, see the pics I upload（also I delete the scaling code, as you can see there are even overlapping）

So my question is why should we use the setTranslationX() method during swiping , the effect on the view's position is like forever.

Answer 1

view.setTranslationX() adds a shift to initial position of the page inside ViewPager. By default pages just go side-by-side. This code:

if (position < 0) {
    view.setTranslationX(horzMargin - vertMargin / 2);
} else {
    view.setTranslationX(-horzMargin + vertMargin / 2);
}

makes them slightly overlaps. Page from the left of the center of ViewPager (position = 0) is shifted to the right and vise versa.