// Copyright (c) 2016 The vulkano developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or https://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

// Welcome to the triangle example!
//
// This is the only example that is entirely detailed. All the other examples avoid code
// duplication by using helper functions.
//
// This example assumes that you are already more or less familiar with graphics programming
// and that you want to learn Vulkan. This means that for example it won't go into details about
// what a vertex or a shader is.

use std::sync::Arc;
use vulkano::buffer::{BufferUsage, CpuAccessibleBuffer, TypedBufferAccess};
use vulkano::command_buffer::{AutoCommandBufferBuilder, CommandBufferUsage, SubpassContents};
use vulkano::device::physical::{PhysicalDevice, PhysicalDeviceType};
use vulkano::device::{Device, DeviceExtensions, Features};
use vulkano::image::view::ImageView;
use vulkano::image::{ImageAccess, ImageUsage, SwapchainImage};
use vulkano::instance::Instance;
use vulkano::pipeline::graphics::input_assembly::InputAssemblyState;
use vulkano::pipeline::graphics::vertex_input::BuffersDefinition;
use vulkano::pipeline::graphics::viewport::{Viewport, ViewportState};
use vulkano::pipeline::GraphicsPipeline;
use vulkano::render_pass::{Framebuffer, RenderPass, Subpass};
use vulkano::swapchain::{self, AcquireError, Swapchain, SwapchainCreationError};
use vulkano::sync::{self, FlushError, GpuFuture};
use vulkano::Version;
use vulkano_win::VkSurfaceBuild;
use winit::event::{Event, WindowEvent};
use winit::event_loop::{ControlFlow, EventLoop};
use winit::window::{Window, WindowBuilder};

fn main() {
    // The first step of any Vulkan program is to create an instance.
    //
    // When we create an instance, we have to pass a list of extensions that we want to enable.
    //
    // All the window-drawing functionalities are part of non-core extensions that we need
    // to enable manually. To do so, we ask the `vulkano_win` crate for the list of extensions
    // required to draw to a window.
    let required_extensions = vulkano_win::required_extensions();

    // Now creating the instance.
    let instance = Instance::new(None, Version::V1_1, &required_extensions, None).unwrap();

    // 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 event_loop = EventLoop::new();
    let surface = WindowBuilder::new()
        .build_vk_surface(&event_loop, instance.clone())
        .unwrap();

    // Choose device extensions that we're going to use.
    // In order to present images to a surface, we need a `Swapchain`, which is provided by the
    // `khr_swapchain` extension.
    let device_extensions = DeviceExtensions {
        khr_swapchain: true,
        ..DeviceExtensions::none()
    };

    // We then choose which physical device to use. First, we enumerate all the available physical
    // devices, then apply filters to narrow them down to those that can support our needs.
    let (physical_device, queue_family) = PhysicalDevice::enumerate(&instance)
        .filter(|&p| {
            // Some devices may not support the extensions or features that your application, or
            // report properties and limits that are not sufficient for your application. These
            // should be filtered out here.
            p.supported_extensions().is_superset_of(&device_extensions)
        })
        .filter_map(|p| {
            // For each physical device, we try to find a suitable queue family that 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. Queues of the same type belong to the same
            // queue family.
            //
            // Here, we look for a single queue family that is suitable for our purposes. In a
            // real-life application, you may want to use a separate dedicated transfer queue to
            // handle data transfers in parallel with graphics operations. You may also need a
            // separate queue for compute operations, if your application uses those.
            p.queue_families()
                .find(|&q| {
                    // We select a queue family that supports graphics operations. When drawing to
                    // a window surface, as we do in this example, we also need to check that queues
                    // in this queue family are capable of presenting images to the surface.
                    q.supports_graphics() && surface.is_supported(q).unwrap_or(false)
                })
                // The code here searches for the first queue family that is suitable. If none is
                // found, `None` is returned to `filter_map`, which disqualifies this physical
                // device.
                .map(|q| (p, q))
        })
        // All the physical devices that pass the filters above are suitable for the application.
        // However, not every device is equal, some are preferred over others. Now, we assign
        // each physical device a score, and pick the device with the
        // lowest ("best") score.
        //
        // In this example, we simply select the best-scoring device to use in the application.
        // In a real-life setting, you may want to use the best-scoring device only as a
        // "default" or "recommended" device, and let the user choose the device themselves.
        .min_by_key(|(p, _)| {
            // We assign a better score to device types that are likely to be faster/better.
            match p.properties().device_type {
                PhysicalDeviceType::DiscreteGpu => 0,
                PhysicalDeviceType::IntegratedGpu => 1,
                PhysicalDeviceType::VirtualGpu => 2,
                PhysicalDeviceType::Cpu => 3,
                PhysicalDeviceType::Other => 4,
            }
        })
        .unwrap();

    // Some little debug infos.
    println!(
        "Using device: {} (type: {:?})",
        physical_device.properties().device_name,
        physical_device.properties().device_type,
    );

    // Now initializing the device. This is probably the most important object of Vulkan.
    //
    // We have to pass four parameters when creating a device:
    //
    // - Which physical device 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.
    //
    // - 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 iterator of created queues is returned by the function alongside the device.
    let (device, mut queues) = Device::new(
        physical_device,
        &Features::none(),
        // Some devices require certain extensions to be enabled if they are present
        // (e.g. `khr_portability_subset`). We add them to the device extensions that we're going to
        // enable.
        &physical_device
            .required_extensions()
            .union(&device_extensions),
        [(queue_family, 0.5)].iter().cloned(),
    )
    .unwrap();

    // Since we can request multiple queues, the `queues` variable is in fact an iterator. We
    // only use one queue in this example, so we just retrieve the first and only element of the
    // iterator.
    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 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_device).unwrap();

        // 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 composite_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 don't specify a value, i.e. `caps.current_extent` is `None`
        // These drivers will allow anything, but the only sensible value is the window dimensions.
        //
        // Both of these cases need the swapchain to use the window dimensions, so we just use that.
        let dimensions: [u32; 2] = surface.window().inner_size().into();

        // Please take a look at the docs for the meaning of the parameters we didn't mention.
        Swapchain::start(device.clone(), surface.clone())
            .num_images(caps.min_image_count)
            .format(format)
            .dimensions(dimensions)
            .usage(ImageUsage::color_attachment())
            .sharing_mode(&queue)
            .composite_alpha(composite_alpha)
            .build()
            .unwrap()
    };

    // We now create a buffer that will store the shape of our triangle.
    // We use #[repr(C)] here to force rustc to not do anything funky with our data, although for this
    // particular example, it doesn't actually change the in-memory representation.
    #[repr(C)]
    #[derive(Default, Debug, Clone)]
    struct Vertex {
        position: [f32; 2],
    }
    vulkano::impl_vertex!(Vertex, position);

    let vertex_buffer = CpuAccessibleBuffer::from_iter(
        device.clone(),
        BufferUsage::all(),
        false,
        [
            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

				layout(location = 0) in vec2 position;

				void main() {
					gl_Position = vec4(position, 0.0, 1.0);
				}
			"
        }
    }

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

				layout(location = 0) out vec4 f_color;

				void main() {
					f_color = vec4(1.0, 0.0, 0.0, 1.0);
				}
			"
        }
    }

    let vs = vs::load(device.clone()).unwrap();
    let fs = fs::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 = vulkano::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 = GraphicsPipeline::start()
        // We need to indicate the layout of the vertices.
        .vertex_input_state(BuffersDefinition::new().vertex::<Vertex>())
        // A Vulkan shader can in theory contain multiple entry points, so we have to specify
        // which one.
        .vertex_shader(vs.entry_point("main").unwrap(), ())
        // The content of the vertex buffer describes a list of triangles.
        .input_assembly_state(InputAssemblyState::new())
        // Use a resizable viewport set to draw over the entire window
        .viewport_state(ViewportState::viewport_dynamic_scissor_irrelevant())
        // See `vertex_shader`.
        .fragment_shader(fs.entry_point("main").unwrap(), ())
        // 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 viewport = Viewport {
        origin: [0.0, 0.0],
        dimensions: [0.0, 0.0],
        depth_range: 0.0..1.0,
    };

    // 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 viewport);

    // 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 = Some(sync::now(device.clone()).boxed());

    event_loop.run(move |event, _, control_flow| {
        match event {
            Event::WindowEvent {
                event: WindowEvent::CloseRequested,
                ..
            } => {
                *control_flow = ControlFlow::Exit;
            }
            Event::WindowEvent {
                event: WindowEvent::Resized(_),
                ..
            } => {
                recreate_swapchain = true;
            }
            Event::RedrawEventsCleared => {
                // 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.as_mut().unwrap().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: [u32; 2] = surface.window().inner_size().into();
                    let (new_swapchain, new_images) =
                        match swapchain.recreate().dimensions(dimensions).build() {
                            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) => return,
                            Err(e) => panic!("Failed to recreate swapchain: {:?}", e),
                        };

                    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 viewport,
                    );
                    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, suboptimal, acquire_future) =
                    match swapchain::acquire_next_image(swapchain.clone(), None) {
                        Ok(r) => r,
                        Err(AcquireError::OutOfDate) => {
                            recreate_swapchain = true;
                            return;
                        }
                        Err(e) => panic!("Failed to acquire next image: {:?}", e),
                    };

                // acquire_next_image can be successful, but suboptimal. This means that the swapchain image
                // will still work, but it may not display correctly. With some drivers this can be when
                // the window resizes, but it may not cause the swapchain to become out of date.
                if suboptimal {
                    recreate_swapchain = true;
                }

                // Specify the color to clear the framebuffer with i.e. blue
                let clear_values = vec![[0.0, 0.0, 1.0, 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 mut builder = AutoCommandBufferBuilder::primary(
                    device.clone(),
                    queue.family(),
                    CommandBufferUsage::OneTimeSubmit,
                )
                .unwrap();

                builder
                    // 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(),
                        SubpassContents::Inline,
                        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 `()`.
                    .set_viewport(0, [viewport.clone()])
                    .bind_pipeline_graphics(pipeline.clone())
                    .bind_vertex_buffers(0, vertex_buffer.clone())
                    .draw(vertex_buffer.len() as u32, 1, 0, 0)
                    .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`.
                let command_buffer = builder.build().unwrap();

                let future = previous_frame_end
                    .take()
                    .unwrap()
                    .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 = Some(future.boxed());
                    }
                    Err(FlushError::OutOfDate) => {
                        recreate_swapchain = true;
                        previous_frame_end = Some(sync::now(device.clone()).boxed());
                    }
                    Err(e) => {
                        println!("Failed to flush future: {:?}", e);
                        previous_frame_end = Some(sync::now(device.clone()).boxed());
                    }
                }
            }
            _ => (),
        }
    });
}

/// 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<RenderPass>,
    viewport: &mut Viewport,
) -> Vec<Arc<Framebuffer>> {
    let dimensions = images[0].dimensions().width_height();
    viewport.dimensions = [dimensions[0] as f32, dimensions[1] as f32];

    images
        .iter()
        .map(|image| {
            let view = ImageView::new(image.clone()).unwrap();
            Framebuffer::start(render_pass.clone())
                .add(view)
                .unwrap()
                .build()
                .unwrap()
        })
        .collect::<Vec<_>>()
}