When rendering offscreen, we want the resulting image to use
premultiplied alpha, since the image will be stored in a texture.
However, when capturing an image in the exporter or test framework,
we want to use straight alpha, so that the resulting image can
be saved as a PNG.
Previously, we incorrectly used straight alpha everywhere, resulting
in incorrect output when using BitmapData.draw with transparency.
* avm2: Implement `BitmapData.draw` for `wgpu` backend
This method requires us to have the ability to render directly to a
texture. Fortunately, the `wgpu` backend already supports this in
the form of `TextureTarget`. However, the rendering code required
some refactoring in order to avoid creating duplicate `wgpu` resources.
The current implementation blocks on copying the pixels back
from the GPU to the CPU, so that we can immediately set them in
the Ruffle `BitmapData`. This is likely very inefficient, but will
work for a first implementation.
In the future, we could explore allowing the CPU image data and GPU
texture to be out of sync, and only synchronized when explicitly
necessary (e.g. on `getPixel` or `setPixel` calls).
* Rename `with_offscreen_backend` to `render_offscreen` and use Bitmap
* Don't panic when backend doesn't implement `render_offscreen`
Previously, the viewport height and width were stored in
both `Stage` and the `RenderBackend`. Any changes to the viewport
dimensions (e.g. due to window resizing) needed to be updated in both
places to keep our handling of the viewport consistent.
This PR adds a new `ViewportDimensions` type, which holds the
width, height, and scale factor. It is stored inside the
`RenderBackend` impl, and is retrieved using the newly added
method `RenderBackend.get_viewport_dimensions`. After a `Player`
has been constructed, any code that needes access to the viewport
dimensions will ultimate go through this method.
Unfortunately, `Stage` needs to use the viewport dimensions
in `build_matrices`. Therefore, any code modifying the viewport
dimensions should go through `player.set_viewport_dimensions`,
which ensures that the stage matrices are rebuilt after the render
backend is updated.
The captured WGPU texture uses premultiplied alpha.
This image gets saved as a PNG, so it should use straight alpha.
Note that all of our current image tests have 'alpha = 1.0' for all
of the pixels, so this currently has no effect.
Based on the work in #6717, plus additional adaptions mentioned in
https://github.com/gfx-rs/wgpu/blob/master/CHANGELOG.md#wgpu-013-2022-06-30,
and more not-mentioned but required changes.
Also bump `wasm-bindgen` to `0.2.81` (along with its helper crates), as
required by the new `wgpu` version.
Note that I don't fully understand some of the required changes, notably:
* `wgpu::PresentMode::Mailbox` no longer works on my machine (Windows 11) -
The `wgpu` documentation says that `wgpu::PresentMode::Fifo` is the
only guaranteed to be supported, so I switched over to it instead.
* `self.staging_belt.recall()` doesn't return a `Future` anymore -
I assume it became synchronous so I simply removed the `executor`
from there.