Functions that manipulate the stack now run inside of `with_current_reader_mut`, which calls a given function with a Reader for the current stack frame. If the stack frame still exists after that code runs, we update it's PC with the Reader's position.
This necessitates the use of a copy of SWF data into the GC arena, along with unsafe (and possibly unsound) pointer manipulation to get the action reader to hold a GC pointer.
Implement the SetTarget2 action, which pops the target off of the
stack, and GetProperty 11, which pushes _target.
However, our implementation of _target is not accurate yet,
because it requires dynamically building the target path. Currently
we fake it by caching the last path to tellTarget.
The AVM1 contains an explicit "target clip" that is used for older
Flash 4-era actions. This target clip can be set to an invalid
value, at which point Play, Stop, etc. will fail silently.
For GetVariable and SetVariable, if the target is invalid,
the variables will be modified on root ("/").
Player is now in charge of scaling/cropping/translating the content
to fit the viewport size supplied by the frontend.
Added backend::render::Letterbox, which stores the margin sizes
for letter/pillarboxing.
Switch from pixels to twips for internal calculations. swf crate
was updated to add a Twips wrapper-type. Ruffle will use this type
internally for transforms and shapes. This fixes some precision
errors in rendering (see heroes_of_cybertron.swf) and will match
what the Flash Player does internally more closely. (e.g.
DisplayObject x and y will be quantized to 1/20 pixel units). It
is up to the renderer to convert units from twip space to pixels
when rendering.