The relative position in rel plugin is currently based on the world coordinate. So for the same effect, like fly in from the right-hand side, we must use different `data-rel-x/y/z` value. Why not let the plugin do the hard part?
So I introduce a `data-rel-position`, when set to `relative`, all relative attribute is based on the position and rotation of previous slide. So no matter the rotation of previous slide, data-rel-x="1000" always looks like fly in from the right-hand side. We can change the position and rotation of one slide, and the position of all following slides will be changed too.
When `data-rel-position` is set to `relative`, relative rotation has a clear meaning. It describes the relative rotations between slides. We don't need to set rotations for all slide, setting the key slides is enough. If `data-rel-position` is not relative, the effect of `data-rel-rotate-x/y/z` is not clear, so they're only used when `data-rel-position="relative"`.
After the introduction of relative rotation, there're 6 attribute that will inherit from previous slide. If we want to set a relative X move, we have to set all other 5 attributes to 0. It's boring. So a `data-rel-clear` is used to set all 6 attributes to 0, and then the value specified in current slide is applied.
The `examples/3D-positions/index.html` shows some usage. As you can see, the html code of two slide ring is the same, and slides except for the first two in a ring has no position attributes. It work by inheriting the previous one.
This PR invokes a lot math calculations. Basically, the rotation of a slide is translated into the coordinate describing the directions of X/Y/Z axes. And `data-rel-x/y/z` can be easily calculated by that. The rotations is the hard part, I mainly use the algorithm in the Quaternions and spatial rotation - Wikipedia to compose two and more rotations. I'm not a math guy, hope I don't make much mistakes.
- Libraries are under src/lib/
- Added to build.js as usual, before plugins.
- See src/lib/README.md for details
gc library implements a "garbage collector" library, which allows
both the core and plugins to store elements and listeners to a list,
and when impress().lib.gc.teardown() is called, to have all of them
removed from the DOM. It also allows plugins to register their own
callback functions, which are called at teardown.
Commentary:
This work is based on copying the src/lib/gc.js from impressionist. While it was
useful, it turns out on the impress.js side there was much more a need to reset
attributes rather than delete elements. For now, this means lots of plugins do this
via their own lib.gc.addCallback() functions. Probably it would be nicer to add
some generic lib.gc.resetAttributes() functionality for this particular case.
I'll return to this in a future patch.
extras/ are not supported for impress().tear(). What can I say, they're extras.
Maybe in the future I'll support them, for now I can live without.
