How to render a custom color under title bar with WGPU on Winit for MacOs

I am creating a rust app which uses winit and wgpu. I set the options

.with_titlebar_transparent(true)

when creating the winit window but I am not sure how to place a color under it. My goal is to make the background color of the content and the title bar the same. I have searched the documentation and repositories of both winit and wgpu but have not found anything. Does someone know how to do this/knows an open source project that did it successfully/if its even possible.

You also need to set .with_fullsize_content_view(true).

Here is a full sample using wgpu:

use std::borrow::Cow;
use winit::{
    event::{Event, WindowEvent},
    event_loop::{ControlFlow, EventLoop},
    platform::macos::WindowBuilderExtMacOS,
    window::Window,
};

const SHADER: &'static str = r##"
@vertex
fn vs_main(@builtin(vertex_index) in_vertex_index: u32) -> @builtin(position) vec4<f32> {
    let x = f32(i32(in_vertex_index) - 1);
    let y = f32(i32(in_vertex_index & 1u) * 2 - 1);
    return vec4<f32>(x, y, 0.0, 1.0);
}

@fragment
fn fs_main() -> @location(0) vec4<f32> {
    return vec4<f32>(1.0, 0.0, 0.0, 1.0);
}
"##;

async fn run(event_loop: EventLoop<()>, window: Window) {
    let size = window.inner_size();

    let instance = wgpu::Instance::default();

    let surface = unsafe { instance.create_surface(&window) }.unwrap();
    let adapter = instance
        .request_adapter(&wgpu::RequestAdapterOptions {
            power_preference: wgpu::PowerPreference::default(),
            force_fallback_adapter: false,
            // Request an adapter which can render to our surface
            compatible_surface: Some(&surface),
        })
        .await
        .expect("Failed to find an appropriate adapter");

    // Create the logical device and command queue
    let (device, queue) = adapter
        .request_device(
            &wgpu::DeviceDescriptor {
                label: None,
                features: wgpu::Features::empty(),
                // Make sure we use the texture resolution limits from the adapter, so we can support images the size of the swapchain.
                limits: wgpu::Limits::downlevel_webgl2_defaults()
                    .using_resolution(adapter.limits()),
            },
            None,
        )
        .await
        .expect("Failed to create device");

    // Load the shaders from disk
    let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
        label: None,
        source: wgpu::ShaderSource::Wgsl(Cow::Borrowed(SHADER)),
    });

    let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
        label: None,
        bind_group_layouts: &[],
        push_constant_ranges: &[],
    });

    let swapchain_capabilities = surface.get_capabilities(&adapter);
    let swapchain_format = swapchain_capabilities.formats[0];

    let render_pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
        label: None,
        layout: Some(&pipeline_layout),
        vertex: wgpu::VertexState {
            module: &shader,
            entry_point: "vs_main",
            buffers: &[],
        },
        fragment: Some(wgpu::FragmentState {
            module: &shader,
            entry_point: "fs_main",
            targets: &[Some(swapchain_format.into())],
        }),
        primitive: wgpu::PrimitiveState::default(),
        depth_stencil: None,
        multisample: wgpu::MultisampleState::default(),
        multiview: None,
    });

    let mut config = wgpu::SurfaceConfiguration {
        usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
        format: swapchain_format,
        width: size.width,
        height: size.height,
        present_mode: wgpu::PresentMode::Fifo,
        alpha_mode: swapchain_capabilities.alpha_modes[0],
        view_formats: vec![],
    };

    surface.configure(&device, &config);

    event_loop.run(move |event, _, control_flow| {
        // Have the closure take ownership of the resources.
        // `event_loop.run` never returns, therefore we must do this to ensure
        // the resources are properly cleaned up.
        let _ = (&instance, &adapter, &shader, &pipeline_layout);

        *control_flow = ControlFlow::Wait;
        match event {
            Event::WindowEvent {
                event: WindowEvent::Resized(size),
                ..
            } => {
                // Reconfigure the surface with the new size
                config.width = size.width;
                config.height = size.height;
                surface.configure(&device, &config);
                // On macos the window needs to be redrawn manually after resizing
                window.request_redraw();
            }
            Event::RedrawRequested(_) => {
                let frame = surface
                    .get_current_texture()
                    .expect("Failed to acquire next swap chain texture");
                let view = frame
                    .texture
                    .create_view(&wgpu::TextureViewDescriptor::default());
                let mut encoder =
                    device.create_command_encoder(&wgpu::CommandEncoderDescriptor { label: None });
                {
                    let mut rpass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                        label: None,
                        color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                            view: &view,
                            resolve_target: None,
                            ops: wgpu::Operations {
                                load: wgpu::LoadOp::Clear(wgpu::Color::GREEN),
                                store: true,
                            },
                        })],
                        depth_stencil_attachment: None,
                    });
                    rpass.set_pipeline(&render_pipeline);
                    rpass.draw(0..3, 0..1);
                }

                queue.submit(Some(encoder.finish()));
                frame.present();
            }
            Event::WindowEvent {
                event: WindowEvent::CloseRequested,
                ..
            } => *control_flow = ControlFlow::Exit,
            _ => {}
        }
    });
}

fn main() {
    let event_loop = EventLoop::new();
    let window = winit::window::WindowBuilder::new()
        .with_title("")
        .with_titlebar_transparent(true)
        .with_fullsize_content_view(true)
        .build(&event_loop)
        .unwrap();

    env_logger::init();
    pollster::block_on(run(event_loop, window));
}

using these dependencies:

env_logger = "0.9"
pollster = "0.2"
wgpu = "0.15.1"
winit = "0.27.1"

you will get