I fail to understand Rust types.

main.rs

#[macro_use]
extern crate vulkano;
extern crate vulkano_shaders;
extern crate winit;
extern crate vulkano_win;

use vulkano::buffer::{CpuAccessibleBuffer, CpuBufferPool, BufferUsage};
use vulkano::command_buffer::{AutoCommandBufferBuilder, DynamicState};
use vulkano::descriptor::descriptor_set::PersistentDescriptorSet;
use vulkano::device::{Device, DeviceExtensions};
use vulkano::format::{ClearValue, Format};
use vulkano::framebuffer::{Framebuffer, FramebufferAbstract, Subpass, RenderPassAbstract};
use vulkano::image::{Dimensions, StorageImage, SwapchainImage};
use vulkano::instance::{Instance, PhysicalDevice};
use vulkano::pipeline::GraphicsPipeline;
use vulkano::pipeline::vertex::{BufferlessDefinition, BufferlessVertices};
use vulkano::pipeline::viewport::Viewport;
// use vulkano::sampler::{Filter, MipmapMode, Sampler, SamplerAddressMode};
use vulkano::swapchain::{AcquireError, PresentMode, SurfaceTransform, Swapchain, SwapchainCreationError};
use vulkano::swapchain;
use vulkano::sync::{GpuFuture, FlushError};
use vulkano::sync;

use vulkano_win::VkSurfaceBuild;

use winit::{EventsLoop, Window, WindowBuilder, Event, WindowEvent,
    KeyboardInput, VirtualKeyCode, ModifiersState, dpi::LogicalSize};

use image;

use std::sync::Arc;

#[cfg(all(debug_assertions))]
const ENABLE_VALIDATION_LAYERS: bool = true;
#[cfg(not(debug_assertions))]
const ENABLE_VALIDATION_LAYERS: bool = false;
const VALIDATION_LAYERS: &[&str] = &["VK_LAYER_LUNARG_standard_validation"];

// type ConcreteGraphicsPipeline = GraphicsPipeline<
//     BufferlessDefinition,
//     Box<PipelineLayoutAbstract + Send + Sync + 'static>,
//     Arc<RenderPassAbstract + Send + Sync + 'static>,
// >;

// type PixelImage = [u8; 4 * 64 * 64];
type PixelImage = [[u8; 4]; 64 * 64];

fn main() {
    let instance = {
        let extensions = vulkano_win::required_extensions();
        if ENABLE_VALIDATION_LAYERS {
            Instance::new(None, &extensions, VALIDATION_LAYERS.iter().map(|s|*s)).unwrap()
        } else {
            Instance::new(None, &extensions, None).unwrap()
        }
    };

    let physical = PhysicalDevice::enumerate(&instance).next().unwrap();
    // println!("Using device: {} (type: {:?})", physical.name(), physical.ty());


    // The objective of this example is to draw a triangle on a window. To do so, we first need to
    // create the window.
    //
    // This is done by creating a `WindowBuilder` from the `winit` crate, then calling the
    // `build_vk_surface` method provided by the `VkSurfaceBuild` trait from `vulkano_win`. If you
    // ever get an error about `build_vk_surface` being undefined in one of your projects, this
    // probably means that you forgot to import this trait.
    //
    // This returns a `vulkano::swapchain::Surface` object that contains both a cross-platform winit
    // window and a cross-platform Vulkan surface that represents the surface of the window.
    let mut events_loop = EventsLoop::new();
    let logical_size: f64 = 544.0;
    let surface = WindowBuilder::new()
        .with_title("Panel Simulator")
        .with_dimensions(LogicalSize::new(logical_size, logical_size))
        .with_resizable(false)
        .build_vk_surface(&events_loop, instance.clone()).unwrap();
    let window = surface.window();

    // The next step is to choose which GPU queue will execute our draw commands.
    //
    // Devices can provide multiple queues to run commands in parallel (for example a draw queue
    // and a compute queue), similar to CPU threads. This is something you have to have to manage
    // manually in Vulkan.
    //
    // In a real-life application, we would probably use at least a graphics queue and a transfers
    // queue to handle data transfers in parallel. In this example we only use one queue.
    //
    // We have to choose which queues to use early on, because we will need this info very soon.
    let queue_family = physical.queue_families().find(|&q| {
        // We take the first queue that supports drawing to our window.
        q.supports_graphics() && surface.is_supported(q).unwrap_or(false)
    }).unwrap();

    // Now initializing the device. This is probably the most important object of Vulkan.
    //
    // We have to pass five parameters when creating a device:
    //
    // - Which physical device (GPU) to connect to.
    //
    // - A list of optional features and extensions that our program needs to work correctly.
    //   Some parts of the Vulkan specs are optional and must be enabled manually at device
    //   creation. In this example the only thing we are going to need is the `khr_swapchain`
    //   extension that allows us to draw to a window.
    //
    // - A list of layers to enable. This is very niche, and you will usually pass `None`.
    //
    // - The list of queues that we are going to use. The exact parameter is an iterator whose
    //   items are `(Queue, f32)` where the floating-point represents the priority of the queue
    //   between 0.0 and 1.0. The priority of the queue is a hint to the implementation about how
    //   much it should prioritize queues between one another.
    //
    // The list of created queues is returned by the function alongside with the device.
    let device_ext = DeviceExtensions { khr_swapchain: true, .. DeviceExtensions::none() };
    let (device, mut queues) = Device::new(physical, physical.supported_features(), &device_ext,
        [(queue_family, 0.5)].iter().cloned()).unwrap();

    // Since we can request multiple queues, the `queues` variable is in fact an iterator. In this
    // example we use only one queue, so we just retrieve the first and only element of the
    // iterator and throw it away.
    let queue = queues.next().unwrap();

    // Before we can draw on the surface, we have to create what is called a swapchain. Creating
    // a swapchain allocates the color buffers that will contain the image that will ultimately
    // be visible on the screen. These images are returned alongside with the swapchain.
    let (mut swapchain, images) = {
        // Querying the capabilities of the surface. When we create the swapchain we can only
        // pass values that are allowed by the capabilities.
        let caps = surface.capabilities(physical).unwrap();

        let usage = caps.supported_usage_flags;

        // The alpha mode indicates how the alpha value of the final image will behave. For example
        // you can choose whether the window will be opaque or transparent.
        let alpha = caps.supported_composite_alpha.iter().next().unwrap();

        // Choosing the internal format that the images will have.
        let format = caps.supported_formats[0].0;

        // The dimensions of the window, only used to initially setup the swapchain.
        // NOTE:
        // On some drivers the swapchain dimensions are specified by `caps.current_extent` and the
        // swapchain size must use these dimensions.
        // These dimensions are always the same as the window dimensions
        //
        // However other drivers dont specify a value i.e. `caps.current_extent` is `None`
        // These drivers will allow anything but the only sensible value is the window dimensions.
        //
        // Because for both of these cases, the swapchain needs to be the window dimensions, we just use that.
        let initial_dimensions = if let Some(dimensions) = window.get_inner_size() {
            // convert to physical pixels
            let dimensions: (u32, u32) = dimensions.to_physical(window.get_hidpi_factor()).into();
            [dimensions.0, dimensions.1]
        } else {
            // The window no longer exists so exit the application.
            return;
        };

        // Please take a look at the docs for the meaning of the parameters we didn't mention.
        Swapchain::new(device.clone(), surface.clone(), caps.min_image_count, format,
            initial_dimensions, 1, usage, &queue, SurfaceTransform::Identity, alpha,
            PresentMode::Fifo, true, None).unwrap()

    };

    // We now create a buffer that will store the shape of our triangle.
    // let vertex_buffer = {
    //     #[derive(Debug, Clone)]
    //     struct Vertex { position: [f32; 2] }
    //     impl_vertex!(Vertex, position);
    //
    //     CpuAccessibleBuffer::from_iter(device.clone(), BufferUsage::all(), [
    //         Vertex { position: [-0.5, -0.25] },
    //         Vertex { position: [0.0, 0.5] },
    //         Vertex { position: [0.25, -0.1] }
    //     ].iter().cloned()).unwrap()
    // };

    // The next step is to create the shaders.
    //
    // The raw shader creation API provided by the vulkano library is unsafe, for various reasons.
    //
    // An overview of what the `vulkano_shaders::shader!` macro generates can be found in the
    // `vulkano-shaders` crate docs. You can view them at https://docs.rs/vulkano-shaders/
    //
    // TODO: explain this in details
    mod vs {
        vulkano_shaders::shader!{
            ty: "vertex",
            src: "
                #version 450
                #extension GL_ARB_separate_shader_objects : enable

                // out gl_perVertex {
                //     vec4 gl_Position;
                // };

                vec2 positions[6] = vec2[](
                    vec2(-1.0, -1.0),
                    vec2(+1.0, -1.0),
                    vec2(-1.0, +1.0),

                    vec2(+1.0, +1.0),
                    vec2(-1.0, +1.0),
                    vec2(+1.0, -1.0)
                );

                void main() {
                    gl_Position = vec4(positions[gl_VertexIndex], 0.0, 1.0);
                }
            "
        }
    }

    mod fs {
        vulkano_shaders::shader!{
            ty: "fragment",
            src: "
                #version 450

                layout(location = 0) out vec4 f_color;

                layout(set = 0, binding = 0, rgba8) uniform readonly image2D pixels;

                void main() {
                    vec2 coord = gl_FragCoord.xy / 1088.0 * 64.0;
                    ivec2 i = ivec2(floor(coord));
                    vec2 f = fract(coord) - 0.5;

                    if (f.x * f.x + f.y * f.y >= 0.16)
                        f_color = vec4(0.0, 0.0, 0.0, 1.0);
                    else
                        // f_color = vec4(i.x / 64.0, i.y / 64.0, 1.0, 1.0);
                        f_color = imageLoad(pixels, i);
                }
                "
        }
    }

    let vs = vs::Shader::load(device.clone()).unwrap();
    let fs = fs::Shader::load(device.clone()).unwrap();

    // At this point, OpenGL initialization would be finished. However in Vulkan it is not. OpenGL
    // implicitly does a lot of computation whenever you draw. In Vulkan, you have to do all this
    // manually.

    // The next step is to create a *render pass*, which is an object that describes where the
    // output of the graphics pipeline will go. It describes the layout of the images
    // where the colors, depth and/or stencil information will be written.
    let render_pass = Arc::new(single_pass_renderpass!(
        device.clone(),
        attachments: {
            // `color` is a custom name we give to the first and only attachment.
            color: {
                // `load: Clear` means that we ask the GPU to clear the content of this
                // attachment at the start of the drawing.
                load: Clear,
                // `store: Store` means that we ask the GPU to store the output of the draw
                // in the actual image. We could also ask it to discard the result.
                store: Store,
                // `format: <ty>` indicates the type of the format of the image. This has to
                // be one of the types of the `vulkano::format` module (or alternatively one
                // of your structs that implements the `FormatDesc` trait). Here we use the
                // same format as the swapchain.
                format: swapchain.format(),
                // TODO:
                samples: 1,
            }
        },
        pass: {
            // We use the attachment named `color` as the one and only color attachment.
            color: [color],
            // No depth-stencil attachment is indicated with empty brackets.
            depth_stencil: {}
        }
    ).unwrap());

    // Before we draw we have to create what is called a pipeline. This is similar to an OpenGL
    // program, but much more specific.
    let pipeline = Arc::new(GraphicsPipeline::start()
        // We need to indicate the layout of the vertices.
        // The type `SingleBufferDefinition` actually contains a template parameter corresponding
        // to the type of each vertex. But in this code it is automatically inferred.
        //.vertex_input_single_buffer()
        .vertex_input(BufferlessDefinition {})
        // A Vulkan shader can in theory contain multiple entry points, so we have to specify
        // which one. The `main` word of `main_entry_point` actually corresponds to the name of
        // the entry point.
        .vertex_shader(vs.main_entry_point(), ())
        // The content of the vertex buffer describes a list of triangles.
        .triangle_list()
        // Use a resizable viewport set to draw over the entire window
        .viewports_dynamic_scissors_irrelevant(1)
        // See `vertex_shader`.
        .fragment_shader(fs.main_entry_point(), ())
        // We have to indicate which subpass of which render pass this pipeline is going to be used
        // in. The pipeline will only be usable from this particular subpass.
        .render_pass(Subpass::from(render_pass.clone(), 0).unwrap())
        // Now that our builder is filled, we call `build()` to obtain an actual pipeline.
        .build(device.clone())
        .unwrap());

    // Dynamic viewports allow us to recreate just the viewport when the window is resized
    // Otherwise we would have to recreate the whole pipeline.
    let mut dynamic_state = DynamicState { line_width: None, viewports: None, scissors: None };

    // The render pass we created above only describes the layout of our framebuffers. Before we
    // can draw we also need to create the actual framebuffers.
    //
    // Since we need to draw to multiple images, we are going to create a different framebuffer for
    // each image.
    let mut framebuffers = window_size_dependent_setup(&images, render_pass.clone(), &mut dynamic_state);

    // Initialization is finally finished!

    // In some situations, the swapchain will become invalid by itself. This includes for example
    // when the window is resized (as the images of the swapchain will no longer match the
    // window's) or, on Android, when the application went to the background and goes back to the
    // foreground.
    //
    // In this situation, acquiring a swapchain image or presenting it will return an error.
    // Rendering to an image of that swapchain will not produce any error, but may or may not work.
    // To continue rendering, we need to recreate the swapchain by creating a new swapchain.
    // Here, we remember that we need to do this for the next loop iteration.
    let mut recreate_swapchain = false;

    // In the loop below we are going to submit commands to the GPU. Submitting a command produces
    // an object that implements the `GpuFuture` trait, which holds the resources for as long as
    // they are in use by the GPU.
    //
    // Destroying the `GpuFuture` blocks until the GPU is finished executing it. In order to avoid
    // that, we store the submission of the previous frame here.
    let mut previous_frame_end = Box::new(sync::now(device.clone())) as Box<GpuFuture>;

    let img_pool: CpuBufferPool<PixelImage> = CpuBufferPool::new(device.clone(), BufferUsage::all());

    // let desc_set = Arc::new(PersistentDescriptorSet::start(pipeline.clone(), 0)
    //     .add_buffer(img_pool.clone()).unwrap()
    //     .build().unwrap()
    // );

    loop {
        // It is important to call this function from time to time, otherwise resources will keep
        // accumulating and you will eventually reach an out of memory error.
        // Calling this function polls various fences in order to determine what the GPU has
        // already processed, and frees the resources that are no longer needed.
        previous_frame_end.cleanup_finished();

        // Whenever the window resizes we need to recreate everything dependent on the window size.
        // In this example that includes the swapchain, the framebuffers and the dynamic state viewport.
        if recreate_swapchain {
            // Get the new dimensions of the window.
            let dimensions = if let Some(dimensions) = window.get_inner_size() {
                let dimensions: (u32, u32) = dimensions.to_physical(window.get_hidpi_factor()).into();
                [dimensions.0, dimensions.1]
            } else {
                return;
            };

            let (new_swapchain, new_images) = match swapchain.recreate_with_dimension(dimensions) {
                Ok(r) => r,
                // This error tends to happen when the user is manually resizing the window.
                // Simply restarting the loop is the easiest way to fix this issue.
                Err(SwapchainCreationError::UnsupportedDimensions) => continue,
                Err(err) => panic!("{:?}", err)
            };

            swapchain = new_swapchain;
            // Because framebuffers contains an Arc on the old swapchain, we need to
            // recreate framebuffers as well.
            framebuffers = window_size_dependent_setup(&new_images, render_pass.clone(), &mut dynamic_state);

            recreate_swapchain = false;
        }

        // Before we can draw on the output, we have to *acquire* an image from the swapchain. If
        // no image is available (which happens if you submit draw commands too quickly), then the
        // function will block.
        // This operation returns the index of the image that we are allowed to draw upon.
        //
        // This function can block if no image is available. The parameter is an optional timeout
        // after which the function call will return an error.
        let (image_num, acquire_future) = match swapchain::acquire_next_image(swapchain.clone(), None) {
            Ok(r) => r,
            Err(AcquireError::OutOfDate) => {
                recreate_swapchain = true;
                continue;
            },
            Err(err) => panic!("{:?}", err)
        };

        // Specify the color to clear the framebuffer with i.e. blue
        let clear_values = vec!([0.0, 0.0, 0.6, 1.0].into());

        // In order to draw, we have to build a *command buffer*. The command buffer object holds
        // the list of commands that are going to be executed.
        //
        // Building a command buffer is an expensive operation (usually a few hundred
        // microseconds), but it is known to be a hot path in the driver and is expected to be
        // optimized.
        //
        // Note that we have to pass a queue family when we create the command buffer. The command
        // buffer will only be executable on that given queue family.
        let vertices = BufferlessVertices {
            vertices: 6,
            instances: 2,
        };

        let mut pixels: PixelImage = [[0; 4]; 64 * 64];
        if let Some(img) = read_img() {
            pixels = img;
        }

        //let img_buffer = img_pool.next(pixels).unwrap();
        let img_buffer = CpuAccessibleBuffer::from_data(
            device.clone(),
            BufferUsage::all(),
            // (0 .. 64 * 64 * 4).map(|_| 0u8))
            [[0u8; 4]; 64 * 64])
            .expect("failed to create buffer");


        let img_img = StorageImage::new(
            device.clone(),
            Dimensions::Dim2d { width: 64, height: 64 },
            Format::R8G8B8A8Unorm, Some(queue.family()),
        ).unwrap();

        let desc_set =
        Arc::new(PersistentDescriptorSet::start(pipeline.clone(), 0)
            .add_image(img_img.clone()).unwrap()
            .build().unwrap()
        );

        let command_buffer =
            AutoCommandBufferBuilder::primary_one_time_submit(
                device.clone(),
                queue.family())
            .unwrap()

            .update_buffer(img_buffer.clone(), pixels)
            .unwrap()

            .clear_color_image(img_img.clone(), ClearValue::Float([0.2, 0.4, 0.0, 1.0]))
            .unwrap()

            .copy_buffer_to_image(img_buffer.clone(), img_img.clone())
            // XXX This line does not compile.  Error is:
            // error[E0271]: type mismatch resolving `<std::sync::Arc<vulkano::buffer::CpuAccessibleBuffer<[[u8; 4]; 4096]>> as vulkano::buffer::TypedBufferAccess>::Content == [_]`
            //    --> src/main.rs:448:14                                                       
            //     |                                                                           
            // 448 |             .copy_buffer_to_image(img_buffer.clone(), img_img.clone())    
            //     |              ^^^^^^^^^^^^^^^^^^^^ expected array of 4096 elements, found slice
            //     |                                                                           
            //     = note: expected type `[[u8; 4]; 4096]`                                     
            //                found type `[_]`                                                 

            .unwrap()

            // Before we can draw, we have to *enter a render pass*. There are two methods to do
            // this: `draw_inline` and `draw_secondary`. The latter is a bit more advanced and is
            // not covered here.
            //
            // The third parameter builds the list of values to clear the attachments with. The API
            // is similar to the list of attachments when building the framebuffers, except that
            // only the attachments that use `load: Clear` appear in the list.
            .begin_render_pass(framebuffers[image_num].clone(), false, clear_values)
            .unwrap()

            // We are now inside the first subpass of the render pass. We add a draw command.
            //
            // The last two parameters contain the list of resources to pass to the shaders.
            // Since we used an `EmptyPipeline` object, the objects have to be `()`.
            // .draw(pipeline.clone(), &dynamic_state, vertex_buffer.clone(), (), ())
            .draw(pipeline.clone(), &dynamic_state, vertices, desc_set.clone(), ())
            .unwrap()

            // We leave the render pass by calling `draw_end`. Note that if we had multiple
            // subpasses we could have called `next_inline` (or `next_secondary`) to jump to the
            // next subpass.
            .end_render_pass()
            .unwrap()

            // Finish building the command buffer by calling `build`.
            .build().unwrap();

        let future = previous_frame_end.join(acquire_future)
            .then_execute(queue.clone(), command_buffer).unwrap()

            // The color output is now expected to contain our triangle. But in order to show it on
            // the screen, we have to *present* the image by calling `present`.
            //
            // This function does not actually present the image immediately. Instead it submits a
            // present command at the end of the queue. This means that it will only be presented once
            // the GPU has finished executing the command buffer that draws the triangle.
            .then_swapchain_present(queue.clone(), swapchain.clone(), image_num)
            .then_signal_fence_and_flush();

        match future {
            Ok(future) => {
                previous_frame_end = Box::new(future) as Box<_>;
            }
            Err(FlushError::OutOfDate) => {
                recreate_swapchain = true;
                previous_frame_end = Box::new(sync::now(device.clone())) as Box<_>;
            }
            Err(e) => {
                println!("{:?}", e);
                previous_frame_end = Box::new(sync::now(device.clone())) as Box<_>;
            }
        }

        update_image();

        // Note that in more complex programs it is likely that one of `acquire_next_image`,
        // `command_buffer::submit`, or `present` will block for some time. This happens when the
        // GPU's queue is full and the driver has to wait until the GPU finished some work.
        //
        // Unfortunately the Vulkan API doesn't provide any way to not wait or to detect when a
        // wait would happen. Blocking may be the desired behavior, but if you don't want to
        // block you should spawn a separate thread dedicated to submissions.

        // Handling the window events in order to close the program when the user wants to close
        // it.
        let mut done = false;

        events_loop.poll_events(|ev| {
            // println!("event = {:?}", ev);
            match ev {
                Event::WindowEvent { event: WindowEvent::CloseRequested, .. } => done = true,
                Event::WindowEvent { event: WindowEvent::Resized(_), .. } => recreate_swapchain = true,
                Event::WindowEvent {
                    event:
                        WindowEvent::KeyboardInput {
                            input:
                                KeyboardInput {
                                    virtual_keycode: Some(VirtualKeyCode::Q),
                                    modifiers:
                                        ModifiersState { logo: true, .. },
                                    ..
                                },
                            ..
                        },
                    ..
                } => done = true,
                Event::WindowEvent {
                    event:
                        WindowEvent::KeyboardInput {
                            input:
                                KeyboardInput {
                                    virtual_keycode: Some(VirtualKeyCode::W),
                                    modifiers:
                                        ModifiersState { logo: true, .. },
                                    ..
                                },
                            ..
                        },
                    ..
                } => done = true,
                _ => ()
            }
            // println!("done = {:?}", done);
        });
        if done { std::process::exit(0); }
    }
}
use image::Pixel;

fn read_img() -> Option<PixelImage> {
    match image::open("/tmp/led-sim/0.png") {
        Err(_) => None,
        Ok(img) => {
            let mut pix: PixelImage = [[0; 4]; 64 * 64];
            for (i, pixel) in img.to_rgba().pixels().enumerate() {
                let (r, g, b, a) = pixel.channels4();
                // let bytes: &[u8] = pixel.channels();
                pix[i] = [r, g, b, a];
                // pix[4 * i + 0] = r;
                // pix[4 * i + 1] = g;
                // pix[4 * i + 2] = b;
                // pix[4 * i + 3] = a;
                if i == 64 * 64 { break; }
            };
            Some(pix)
        }
    }
}

#[allow(unused)]
fn update_image() {
    // create dir if needed
    // check that dir is readable and executable
    // look for new files
    //
}

/// This method is called once during initialization, then again whenever the window is resized
fn window_size_dependent_setup(
    images: &[Arc<SwapchainImage<Window>>],
    render_pass: Arc<RenderPassAbstract + Send + Sync>,
    dynamic_state: &mut DynamicState
) -> Vec<Arc<FramebufferAbstract + Send + Sync>> {
    let dimensions = images[0].dimensions();

    let viewport = Viewport {
        origin: [0.0, 0.0],
        dimensions: [dimensions[0] as f32, dimensions[1] as f32],
        depth_range: 0.0 .. 1.0,
    };
    dynamic_state.viewports = Some(vec!(viewport));

    images.iter().map(|image| {
        Arc::new(
            Framebuffer::start(render_pass.clone())
                .add(image.clone()).unwrap()
                .build().unwrap()
        ) as Arc<FramebufferAbstract + Send + Sync>
    }).collect::<Vec<_>>()
}