In the horizontal pager loading the previous chapter caused the scroll position to get lost and instead of starting at the end of the previous chapter, the scroll position was at the very start.
This happened everytime no matter if the scroll position was at the x 0 or not before the previous chapter got visible.
Same issue can be observed in the vertical pager in case the scroll position is at y 0 before the previous chapter has been rendered.
The viewers can have different sizes which caused theme to not be properly centered.
E.g. for the "vertical mode" in case "chapter 1" is greater in width than "chapter 2", the pages of "chapter 2" were not correctly centered due to the "viewers" having different widths.
In case many chapters are rendered, even just the HOC wrapper component re-render due to the context change increases the render time.
Thus, getting rid of these HOC wrapper re-renders by moving the context usage up to the ReaderViewer decreases the render time.
In case many chapters are rendered, even just the HOC wrapper component re-render due to the context change increases the render time.
Thus, getting rid of these HOC wrapper re-renders by moving the context usage up to the ReaderViewer decreases the render time.
By the time the scroll area got scrolled to the start of the visible pages, the previous/next page wasn't yet shown and thus, the scrollable area wasn't updated yet.
Thus, in case the scrollable area grew in width due to the page change, the start never got scrolled into view due to triggering the logic too early.
Instead of immediately updating the value once the page count changed, it got updated after "pagesToSpreadState" changed, which was after the rendering finished.
This was the actual root cause of what was tried to be fixed with 9ab6ec89c7
Since "pagesToSpreadState" isn't part of the dependency array and also would decrease the render performance if it was (see reasoning of c79f7cc874), the array reference might be out of date and thus, the guard might not work correctly
In case the current page changed after selecting a page, the previously selected page couldn't be selected again since the "pageToScrollToIndex" was still set to this page
Due to handling an "offset spread page" change as if the "double page" mode got activated, the index of the secondary page was set, which resulted in opening the next page
Depending on the screen size and e.g. the set "reader width" pages might not have filled out the full img elements size due to "object-fit contain".
This was caused due to the image wrappers flex container "align-items center" which slightly reduced the images width to some ".xy" number (e.g. instead of wrappers width 258px, the images were something like 257.83px)
In case the last page of a manga was immediately visible or the became visible after the "image spread state" change, the chapter never got marked as read
Due to the way the pages got scrolled into view, the current page was not changed to the new page.
This then prevented the previous/next page to get opened via click/hotkey actions
