Document vertical centering breaking backcompat

Essentially, slides have variable height now. This is not normally visible, but with transitions that have a non-transparent background, like `cube` or `page`, it is:

http://lab.hakim.se/reveal-js/?transition=cube

Before, slides had a fixed height, which means that presentations designed with that assumption in mind will look very different now.

Another aspect that I bumped into is that I used the slide's height to dynamically size images to fill the remainder of the space from the heading to the footer, like this (stripped to the essence):

          bigImage.style.height = section.offsetHeight - bigImage.offsetTop + 'px';

Alternatively, is there an easy way to restore the previous functionality?

diff --git a/README.md b/README.md
index 6c07a33a0630ef802f628be344da076aeed26cda..0d6e3acabf266b64897e4b42702b29b0e1d36c9b 100644 (file)
--- a/README.md
+++ b/README.md
@@ -93,6 +93,8 @@ Reveal.initialize({
 });
 ```
 
+Note that the new default vertical centering option will break compatibility with slides that were using transitions with backgrounds (`cube` and `page`). To restore the previous behavior, set `center` to `false`.
+
 ### Dependencies
 
 Reveal.js doesn't _rely_ on any third party scripts to work but a few optional libraries are included by default. These libraries are loaded as dependencies in the order they appear, for example: