Japanese RTL vertical writing mode, page selection based on rectangle visibility trailing instead of leading "edge" (CfiNavigationLogic)

[danielweck]

See:
#87
#113

When an element (e.g. a run of text) spans across two (or more) consecutive "pages" (a "page" is effectively a CSS column, which ; in vertical writing mode ; always fills the entire iframe viewport, as there is no two-page synthetic spread), such element is considered "visible" based on the visibility of the trailing text (i.e. bottom-left corner of the bounding box / client rectangles). This results in the last page being selected, instead of the first. In other word, when hyperlinking to an element that spans from one page to another, the algorithm should bring to view the "leading edge" (e.g. beginning of a sentence), i.e. the top-right corner of the bounding box / client rectangles. You can test this behaviour by playing the Media Overlays of Kusamakura (chapters 1,2,3), and by using the previous/next buttons in the MO control panel to transition from one page to the next (forwards from right to left, then backwards).

EPUB:
https://code.google.com/p/epub-samples/downloads/detail?name=kusamakura-japanese-vertical-writing-20121124.epub

[danielweck]

Is that fixed by Juan's PR? ( @jccr )
#210