code: public void setPageTransformer(boolean reverseDrawingOrder, ViewPager.PageTransformer transformer) {
          if (Build.VERSION.SDK_INT >= 11) {
              final boolean hasTransformer = transformer != null;
              final boolean needsPopulate = hasTransformer != (mPageTransformer != null);
              mPageTransformer = transformer;
              setChildrenDrawingOrderEnabledCompat(hasTransformer);
              if (hasTransformer) {
                  mDrawingOrder = reverseDrawingOrder ? DRAW_ORDER_REVERSE : DRAW_ORDER_FORWARD;
              } else {
                  mDrawingOrder = DRAW_ORDER_DEFAULT;
              }
              if (needsPopulate) populate();
          }
      }
docs: Set a {@link ViewPager.PageTransformer} that will be called for each attached page whenever
  the scroll position is changed. This allows the application to apply custom property
  transformations to each page, overriding the default sliding look and feel.
  <p/>
  <p><em>Note:</em> Prior to Android 3.0 the property animation APIs did not exist.
  As a result, setting a PageTransformer prior to Android 3.0 (API 11) will have no effect.</p>
  
  @param reverseDrawingOrder true if the supplied PageTransformer requires page views
  to be drawn from last to first instead of first to last.
  @param transformer         PageTransformer that will modify each page's animation properties