When using the bitmap.wgsl shader for normal rendering, we need
to saturate immediately after applying the color transformation
to reproduce Flash Player's behavior. This makes the (possibly
transformed) alpha value get multiplied by a in-range color,
instead of a potentially out-of-range color.
However, Stage3D just applies a no-op color transformation,
and should only saturate at the very end
(not after the intermediate division by the original alpha value).
To support both of these requirements, I've added in a new
`early_saturate` ifdef that controls when we apply 'saturate'.
We then compile the shader twice (once with early_saturate=true
and once with early_saturate=false), and use the two versions
in the right pipelines.
We could use a simpler shader for Stage3D - however, it can't just
be a plain copy, as we need to apply the viewport transformation.
For now, I'm re-using the shader code to keep things simple. If
this becomes a performance issue in stage3d, we could revisit this.
Each render backend keeps track of a stack of BlenModes,
which are pushed and popped by 'core' as we render objects
in the displaay tree. For now, I've just implemented BlendMode.ADD,
which maps directly onto blend mode supported by each backend.
All other blend modes (besides 'NORMAL') will produce a warning
when we try to render using them. This may produce a very large amount
of log output, but it's simpler than emitting each warning only once,
and will help to point developers in the right direction when they
get otherwise inexplicable rendering issues (due to a blend mode
not being implemented).
The wgpu implementation is by far the most complicated, as we need
to construct a `RenderPipeline` for each possible
`(BlendMode, MaskState)`. I haven't been able to find any documentation
about the maximum supported number of (simultaneous) WebGPU render
pipelines - if this becomes an issue, we may need to register them
on-demand when a particular blend mode is requested.
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.
Kamil Jarosz