`BitmapHandle` now holds `Arc<dyn BitmapHandleImpl>`.
This allows us to move all of the per-bitmap backend data into
`BitmapHandle`, instead of holding an id to a backend-specific
hashmap.
This fixes the memory leak issue with bitmaps. Once the AVM side of a
bitmap (`Bitmap`/`BitmapData`) gets garbage-collected, the
`BitmapHandle` will get dropped, freeing all of the GPU resources
assoicated with the bitmap.
This PR implements core 'stage3D' APIs. We are now able
to render at least two demos from the Context3D docs - a simple
triangle render, and a rotating cube.
Implemented in this PR:
* Stage3D access and Context3D creation
* IndexBuffer3D and VertexBuffer3D creation, uploading, and usage
* Program3D uploading and usage (via `naga-agal`)
* Context3D: configureBackBuffer, clear, drawTriangles, and present
Not yet implemented:
* Any 'dispose()' methods
* Depth and stencil buffers
* Context3D texture apis
* Scissor rectangle
General implementation strategy:
A new `Object` variant is added for each of the Stage3D objects
(VertexBuffer3D, Program3D, etc). This stores a handle to the
parent `Context3D`, and (depending on the object) a handle
to the underlying native resource, via `Rc<dyn
SomeRenderBackendTrait>`).
Calling methods on Context3D does not usually result in an immediate
call to a `wgpu` method. Instead, we queue up commands in our
`Context3D` instance, and execute them all on a call to `present`.
This avoids some nasty wgpu lifetime issues, and is very similar
to the approah we use for normal rendering.
The actual rendering happens on a `Texture`, with dimensions
determined by `createBackBuffer`. During 'Stage' rendering,
we render all of these Stage3D textures *behind* the normal
stage (but in front of the overall stage background color).
Nathan Adams