[Merged by Bors] - Camera Output Modes, MSAA Writeback, and BlitPipeline

[cart]

Objective

Alternative to #7490. I wrote all of the code in this PR, but I have added @robtfm as co-author on commits that build on ideas from #7490. I would not have been able to solve these problems on my own without much more time investment and I'm largely just rephrasing the ideas from that PR.

Fixes #7435
Fixes #7361
Fixes #5721

Solution

This implements the solution I outlined here.

• Adds "msaa writeback" as an explicit "msaa camera feature" and default to msaa_writeback: true for each camera. If this is true, a camera has MSAA enabled, and it isn't the first camera for the target, add a writeback before the main pass for that camera.
• Adds a CameraOutputMode, which can be used to configure if (and how) the results of a camera's rendering will be written to the final RenderTarget output texture (via the upscaling node). The blend_state and color_attachment_load_op are now configurable, giving much more control over how a camera will write to the output texture.
• Made cameras with the same target share the same main_texture tracker by using Arc<AtomicUsize>, which ensures continuity across cameras. This was previously broken / could produce weird results in some cases. ViewTarget::main_texture() is now correct in every context.
• Added a new generic / specializable BlitPipeline, which the new MsaaWritebackNode uses internally. The UpscalingPipelineNode now uses BlitPipeline instead of its own pipeline. We might ultimately need to fork this back out if we choose to add more configurability to the upscaling, but for now this will save on binary size by not embedding the same shader twice.
• Moved the "camera sorting" logic from the camera driver node to its own system. The results are now stored in the SortedCameras resource, which can be used anywhere in the renderer. MSAA writeback makes use of this.

---

Changelog

• Added Camera::msaa_writeback which can enable and disable msaa writeback.
• Added specializable BlitPipeline and ported the upscaling node to use this.
• Added SortedCameras, exposing information that was previously internal to the camera driver node.
• Made cameras with the same target share the same main_texture tracker, which ensures continuity across cameras.

[IceSentry]

This might be a bit too advanced to have the example in the repo, but do you have a gist of how you would use this to fix #7435? I'm not entirely sure how I would need to use this to make it work correctly.

[cart]

@IceSentry the msaa writeback (which is enabled by default in this pr) should fix #7435 automatically. When I made the changes to split_screen mentioned in that issue, bloom showed up on the left side as expected.

[rparrett]

Ditto #7361

[cart]

@rparrett this also works as expected by default for me.

[rparrett]

@rparrett this also works as expected by default for me.

With the example in #7361, I would expect only the hexagon to get bloom, but with this PR, only the circle does.

[cart]

@rparrett haha yup you're right.

First: I needed to re-add the bloom upsampling alpha blending from the other PR. (see latest commit).

From there, this camera setup works, which configures what amounts to the same setup from #7490:

    // No special config required here. This will write to the output texture by default 
    commands.spawn((
        Camera2dBundle {
            camera: Camera {
                hdr: true,
                ..default()
            },
            ..default()
        },
        no_bloom_layer,
    ));

    commands.spawn((
        Camera2dBundle {
            camera_2d: Camera2d {
                // Transparent clear color to ensure this layers on top of the output correctly
                clear_color: ClearColorConfig::Custom(Color::NONE),
                ..default()
            },
            camera: Camera {
                hdr: true,
                // Disable MSAA writeback as we don't want the last camera's outputs in our
                // intermediate multisampled textures
                msaa_writeback: false,
                order: 1,
               // Write to the output texture, but load the previous state + blend 
                output_mode: CameraOutputMode::Write {
                    blend_state: Some(BlendState::ALPHA_BLENDING),
                    color_attachment_load_op: LoadOp::Load,
                },
                ..default()
            },
            ..default()
        },
        bloom_layer,
        BloomSettings {
            threshold: 0.5,
            intensity: 1.0,
            ..default()
        },
    ));

[cart]

Also for completeness I will confirm that #5721 works out of the box now.

[robtfm]

just one typo to prove i read it.

i think personally i'd prefer having the more intelligent defaults, definitely for writeback and maybe for the clear color, but this does expose everything needed as it stands.

[cart]

i think personally i'd prefer having the more intelligent defaults, definitely for writeback and maybe for the clear color, but this does expose everything needed as it stands.

I'm definitely down to explore something closer to the "smarts" of your previous impl for writeback (maybe in an opt-in, but enabled by default fashion). Feel free to follow this up if you're interested. (not for 0.10 though 😄 )

[cart]

bors r+

[bors]

Pull request successfully merged into main.

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