gpui: Enable MSAA to Path render for Anti-Aliasing

[huacnlee]

Closes #20762

Release Notes:

• N/A

---

Enable MSAA for Anti-Aliasing to Path (cx.paint_path) for drawing a better vector graphics.

cargo run -p gpui --example gradient --features macos-blade
cargo run -p gpui --example gradient

cargo run -p gpui --example painting --features macos-blade
cargo run -p gpui --example painting

Before

After

TODO

• Support Metal.
• Detect system support to set up sample count.
• Fix extra lines between Path vertices

Ref kvark/blade#213

Ask @kvark to review.

I am not sure if there is anything I missed. I modified it according to the particle example of Blade project. But the difference is that after the first MSAA render, I did not do it a second time, I tested it and found it was not necessary.

Before

if let mut pass = self.command_encoder.render(
    "draw particles with msaa resolve",
    gpu::RenderTargetSet {
        colors: &[gpu::RenderTarget {
            view: self.msaa_view.unwrap(),
            init_op: gpu::InitOp::Clear(gpu::TextureColor::OpaqueBlack),
            finish_op: gpu::FinishOp::ResolveTo(frame_view),
        }],
        depth_stencil: None,
    },
) {
    self.particle_system
        .draw(&mut pass, screen_desc.physical_size);
}
if let mut pass = self.command_encoder.render(
    "draw ui",
    gpu::RenderTargetSet {
        colors: &[gpu::RenderTarget {
            view: frame_view,
            init_op: gpu::InitOp::Load,
            finish_op: gpu::FinishOp::Store,
        }],
        depth_stencil: None,
    },
) {
    self.gui_painter
        .paint(&mut pass, gui_primitives, screen_desc, &self.context);
}

After

if let mut pass = self.command_encoder.render(
    "draw particles with msaa resolve",
    gpu::RenderTargetSet {
        colors: &[gpu::RenderTarget {
            view: self.msaa_view.unwrap(),
            init_op: gpu::InitOp::Clear(gpu::TextureColor::OpaqueBlack),
            finish_op: gpu::FinishOp::ResolveTo(frame_view),
        }],
        depth_stencil: None,
    },
) {
    self.particle_system
        .draw(&mut pass, screen_desc.physical_size);
    self.gui_painter
        .paint(&mut pass, gui_primitives, screen_desc, &self.context);
}

It looks no difference?

[huacnlee]

After turning on MSAA, an unexpected connection line will appear between the start point of the Path drawing and other corners.

Like this:

[huacnlee]

Try a Shader change to use gather

Improve path_sprite_fragment to use gather to sample avg with 4 points.

✅ UPDATE: Is looks like not need to do this, reverted this change.

Before

After

Same case in Sketch

[huacnlee]

After turning on MSAA, an unexpected connection line will appear between the start point of the Path drawing and other corners.

Like this:

I'm stuck with this line problem. I've been looking for possible reasons for the past two days, but still can't solve it. 🤔

[kvark]

Nice work!

[kvark]

the argument should say explicitly that it's only for the path rasterization, e.g. path_sample_count

[kvark]

do you really need the query? pretty sure the sample count of 4 is universally supported on all platforms

[huacnlee]

Oh, here is a reference:

https://developer.apple.com/documentation/metal/mtldevice/1433355-supportstexturesamplecount

Sample Count	Devices
1	All devices
2	All iOS devices All tvOS devices Some macOS devices
4	All devices
8	Some macOS devices

[kvark]

This is a bit wasteful. We only want MSAA atlas tiles for things that actually require MSAA.
The atlas contains texture of different formats via AtlasTextureKind.
A general way to implement it is to turn BladeAtlasStorage into basically a HashMap<BladeAtlasKey, AtlasTextureList<BladeAtlasTexture>>, where BladeAtlasKey would be a combination of both AtlasTextureKind and the sample count.

A less general way would be to just make it explicitly path_sample_count, so that it only affects the rasterized path.
Honestly, I think this is a better way due to its simplicity.

[huacnlee]

Makes sense.

I have changed only Path kind to create msaa_texutre

[kvark]

this should be slightly different

let color_target = if let Some(msaa_view) = tex_info.msaa_view {
gpu::RenderTarget {
                        view: tex_info.raw_view,
                        view: msaa_view,
                        init_op: gpu::InitOp::Clear(gpu::TextureColor::OpaqueBlack),
                        finish_op: gpu::FinishOp::ResolveTo(frame_view),
                    }
} else {
gpu::RenderTarget {
                        view: frame_view,
                        init_op: gpu::InitOp::Clear(gpu::TextureColor::OpaqueBlack),
                        finish_op: gpu::FinishOp::Store,
                    }
}

[huacnlee]

Do you means should rename render_target to color_target? Or is other I missed?

Because the code that you given, there have a mistake (duplicate view), so I'm not sure.