// Copyright (c) 2016 The vulkano developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://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.

// For the purpose of this example all unused code is allowed.
#![allow(dead_code)]

// The `vulkano` crate is the main crate that you must use to use Vulkan.
#[macro_use]
extern crate vulkano;
// The `vulkano_shader_derive` crate allows us to use the `VulkanoShader` custom derive that we use
// in this example.
#[macro_use]
extern crate vulkano_shader_derive;
// However the Vulkan library doesn't provide any functionality to create and handle windows, as
// this would be out of scope. In order to open a window, we are going to use the `winit` crate.
extern crate winit;
// The `vulkano_win` crate is the link between `vulkano` and `winit`. Vulkano doesn't know about
// winit, and winit doesn't know about vulkano, so import a crate that will provide a link between
// the two.
extern crate vulkano_win;

use vulkano_win::VkSurfaceBuild;

use vulkano::buffer::BufferUsage;
use vulkano::buffer::CpuAccessibleBuffer;
use vulkano::command_buffer::AutoCommandBufferBuilder;
use vulkano::command_buffer::DynamicState;
use vulkano::device::Device;
use vulkano::framebuffer::Framebuffer;
use vulkano::framebuffer::Subpass;
use vulkano::instance::Instance;
use vulkano::pipeline::GraphicsPipeline;
use vulkano::pipeline::viewport::Viewport;
use vulkano::swapchain;
use vulkano::swapchain::PresentMode;
use vulkano::swapchain::SurfaceTransform;
use vulkano::swapchain::Swapchain;
use vulkano::swapchain::AcquireError;
use vulkano::swapchain::SwapchainCreationError;
use vulkano::sync::now;
use vulkano::sync::GpuFuture;

use vulkano::image::{AttachmentImage, ImageAccess};
use vulkano::format::{Format, ClearValue};

use std::iter;
use std::sync::Arc;
use std::mem;

fn main() {
    // The first step of any vulkan program is to create an instance.
    let 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 extensions = vulkano_win::required_extensions();

        // Now creating the instance.
        Instance::new(None, &extensions, None).expect("failed to create Vulkan instance")
    };

    // We then choose which physical device to use.
    //
    // In a real application, there are three things to take into consideration:
    //
    // - Some devices may not support some of the optional features that may be required by your
    //   application. You should filter out the devices that don't support your app.
    //
    // - Not all devices can draw to a certain surface. Once you create your window, you have to
    //   choose a device that is capable of drawing to it.
    //
    // - You probably want to leave the choice between the remaining devices to the user.
    //
    // For the sake of the example we are just going to use the first device, which should work
    // most of the time.
    let physical = vulkano::instance::PhysicalDevice::enumerate(&instance)
                            .next().expect("no device available");
    // Some little debug infos.
    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_win::Window` 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 = winit::EventsLoop::new();
    let window = winit::WindowBuilder::new().build_vk_surface(&events_loop, instance.clone()).unwrap();

    // 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 = physical.queue_families().find(|&q| {
        // We take the first queue that supports drawing to our window.
        q.supports_graphics() && window.surface().is_supported(q).unwrap_or(false)
    }).expect("couldn't find a graphical queue family");

    // 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 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, mut queues) = {
        let device_ext = vulkano::device::DeviceExtensions {
            khr_swapchain: true,
            .. vulkano::device::DeviceExtensions::none()
        };

        Device::new(physical, physical.supported_features(), &device_ext,
                    [(queue, 0.5)].iter().cloned()).expect("failed to create device")
    };

    // 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 retreive the first and only element of the
    // iterator and throw it away.
    let queue = queues.next().unwrap();

    // The dimensions of the surface.
    // This variable needs to be mutable since the viewport can change size.
    let mut dimensions;

    // 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, mut 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 = window.surface().capabilities(physical)
                         .expect("failed to get surface capabilities");

        dimensions = caps.current_extent.unwrap_or([1024, 768]);

        // We choose the dimensions of the swapchain to match the current extent of the surface.
        // If `caps.current_extent` is `None`, this means that the window size will be determined
        // by the dimensions of the swapchain, in which case we just use the width and height defined above.

        // 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;

        // Please take a look at the docs for the meaning of the parameters we didn't mention.
        Swapchain::new(device.clone(), window.surface().clone(), caps.min_image_count, format,
                       dimensions, 1, caps.supported_usage_flags, &queue,
                       SurfaceTransform::Identity, alpha, PresentMode::Fifo, true,
                       None).expect("failed to create swapchain")
    };

    // 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()).expect("failed to create buffer")
    };

    // The next step is to create the shaders.
    //
    // The raw shader creation API provided by the vulkano library is unsafe, for various reasons.
    //
    // TODO: explain this in details
    mod vs {
        #[derive(VulkanoShader)]
        #[ty = "vertex"]
        #[src = "
#version 450

layout(location = 0) in vec2 position;

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

    mod fs {
        #[derive(VulkanoShader)]
        #[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);
}
"]
        struct Dummy;
    }

    let vs = vs::Shader::load(device.clone()).expect("failed to create shader module");
    let fs = fs::Shader::load(device.clone()).expect("failed to create shader module");

    // At this point, OpenGL initialization would be finished. However in Vulkan it is not. OpenGL
    // implicitely 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: {
            multisample_color: {
                load: Clear,
                store: DontCare,
                format: swapchain.format(),
                samples: 8,
            },
            multisampled_depth: {
                load:    Clear,
                store:   DontCare,
                format:  Format::D16Unorm,
                samples: 8,
            },
            resolve_color: {
                load: DontCare,
                store: Store,
                format: swapchain.format(),
                samples: 1,
            },
            resolve_depth: {
                load:    DontCare,
                store:   Store,
                format:  Format::D16Unorm,
                samples: 1,
                initial_layout: ImageLayout::Undefined,
                final_layout: ImageLayout::DepthStencilAttachmentOptimal,
            }
        },
        pass: {
            color: [multisample_color],
            depth_stencil: {multisampled_depth},
            resolve: [resolve_color],
        }
    ).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()
        // 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());

    // 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: Option<Vec<Arc<vulkano::framebuffer::Framebuffer<_,_>>>> = None;

    // 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(now(device.clone())) as Box<GpuFuture>;

    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();

        // If the swapchain needs to be recreated, recreate it
        if recreate_swapchain {
            // Get the new dimensions for the viewport/framebuffers.
            dimensions = window.surface().capabilities(physical)
                        .expect("failed to get surface capabilities")
                        .current_extent.unwrap();

            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)
            };

            mem::replace(&mut swapchain, new_swapchain);
            mem::replace(&mut images, new_images);

            framebuffers = None;

            recreate_swapchain = false;
        }

        // Because framebuffers contains an Arc on the old swapchain, we need to
        // recreate framebuffers as well.
        if framebuffers.is_none() {
            let new_framebuffers = Some(images.iter().map(|image| {
                let dim = image.dimensions().width_height();
                let multisample_image = AttachmentImage::transient_multisampled(device.clone(), dim, 8, image.format()).unwrap();
                let multisample_depth = AttachmentImage::transient_multisampled(device.clone(), dim, 8, Format::D16Unorm).unwrap();
                let depth = AttachmentImage::transient(device.clone(), dim, Format::D16Unorm).unwrap();
                Arc::new(Framebuffer::start(render_pass.clone())
                         .add(multisample_image.clone()).unwrap()
                         .add(multisample_depth.clone()).unwrap()
                         .add(image.clone()).unwrap()
                         .add(depth.clone()).unwrap()
                         .build().unwrap())
            }).collect::<Vec<_>>());
            mem::replace(&mut framebuffers, new_framebuffers);
        }

        // 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)
        };

        // 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 command_buffer = AutoCommandBufferBuilder::primary_one_time_submit(device.clone(), queue.family()).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.as_ref().unwrap()[image_num].clone(), false,
                               vec![[0.0, 0.0, 1.0, 1.0].into(), 1f32.into(), ClearValue::None, ClearValue::None])
            .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(),
                  DynamicState {
                      line_width: None,
                      // TODO: Find a way to do this without having to dynamically allocate a Vec every frame.
                      viewports: Some(vec![Viewport {
                          origin: [0.0, 0.0],
                          dimensions: [dimensions[0] as f32, dimensions[1] as f32],
                          depth_range: 0.0 .. 1.0,
                      }]),
                      scissors: None,
                  },
                  vertex_buffer.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().unwrap();
        previous_frame_end = Box::new(future) as Box<_>;

        // 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| {
            match ev {
                winit::Event::WindowEvent { event: winit::WindowEvent::Closed, .. } => done = true,
                _ => ()
            }
        });
        if done { return; }
    }
}