snow_trail/src/postprocess.rs

use bytemuck::{Pod, Zeroable};

#[repr(C)]
#[derive(Clone, Copy, Pod, Zeroable)]
pub struct ScreenVertex
{
    pub position: [f32; 2],
    pub uv: [f32; 2],
}

impl ScreenVertex
{
    pub fn desc() -> wgpu::VertexBufferLayout<'static>
    {
        wgpu::VertexBufferLayout {
            array_stride: std::mem::size_of::<ScreenVertex>() as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Vertex,
            attributes: &[
                wgpu::VertexAttribute {
                    offset: 0,
                    shader_location: 0,
                    format: wgpu::VertexFormat::Float32x2,
                },
                wgpu::VertexAttribute {
                    offset: std::mem::size_of::<[f32; 2]>() as wgpu::BufferAddress,
                    shader_location: 1,
                    format: wgpu::VertexFormat::Float32x2,
                },
            ],
        }
    }
}

pub struct LowResFramebuffer
{
    pub texture: wgpu::Texture,
    pub view: wgpu::TextureView,
    pub depth_view: wgpu::TextureView,
    pub sampler: wgpu::Sampler,
    pub width: u32,
    pub height: u32,
}

impl LowResFramebuffer
{
    pub fn new(device: &wgpu::Device, width: u32, height: u32, format: wgpu::TextureFormat)
        -> Self
    {
        let size = wgpu::Extent3d {
            width,
            height,
            depth_or_array_layers: 1,
        };

        let texture = device.create_texture(&wgpu::TextureDescriptor {
            label: Some("Low Res Color Texture"),
            size,
            mip_level_count: 1,
            sample_count: 1,
            dimension: wgpu::TextureDimension::D2,
            format,
            usage: wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::TEXTURE_BINDING,
            view_formats: &[],
        });

        let view = texture.create_view(&wgpu::TextureViewDescriptor::default());

        let depth_texture = device.create_texture(&wgpu::TextureDescriptor {
            label: Some("Low Res Depth Texture"),
            size,
            mip_level_count: 1,
            sample_count: 1,
            dimension: wgpu::TextureDimension::D2,
            format: wgpu::TextureFormat::Depth32Float,
            usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
            view_formats: &[],
        });

        let depth_view = depth_texture.create_view(&wgpu::TextureViewDescriptor::default());

        let sampler = device.create_sampler(&wgpu::SamplerDescriptor {
            label: Some("Low Res Sampler"),
            address_mode_u: wgpu::AddressMode::ClampToEdge,
            address_mode_v: wgpu::AddressMode::ClampToEdge,
            address_mode_w: wgpu::AddressMode::ClampToEdge,
            mag_filter: wgpu::FilterMode::Nearest,
            min_filter: wgpu::FilterMode::Nearest,
            mipmap_filter: wgpu::FilterMode::Nearest,
            ..Default::default()
        });

        Self {
            texture,
            view,
            depth_view,
            sampler,
            width,
            height,
        }
    }
}

pub fn create_fullscreen_quad(device: &wgpu::Device) -> (wgpu::Buffer, wgpu::Buffer, u32)
{
    use wgpu::util::DeviceExt;

    let vertices = [
        ScreenVertex {
            position: [-1.0, -1.0],
            uv: [0.0, 1.0],
        },
        ScreenVertex {
            position: [1.0, -1.0],
            uv: [1.0, 1.0],
        },
        ScreenVertex {
            position: [1.0, 1.0],
            uv: [1.0, 0.0],
        },
        ScreenVertex {
            position: [-1.0, 1.0],
            uv: [0.0, 0.0],
        },
    ];

    let indices: [u16; 6] = [0, 1, 2, 2, 3, 0];

    let vertex_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
        label: Some("Fullscreen Quad Vertex Buffer"),
        contents: bytemuck::cast_slice(&vertices),
        usage: wgpu::BufferUsages::VERTEX,
    });

    let index_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
        label: Some("Fullscreen Quad Index Buffer"),
        contents: bytemuck::cast_slice(&indices),
        usage: wgpu::BufferUsages::INDEX,
    });

    (vertex_buffer, index_buffer, indices.len() as u32)
}

pub fn create_blit_pipeline(
    device: &wgpu::Device,
    format: wgpu::TextureFormat,
    bind_group_layout: &wgpu::BindGroupLayout,
) -> wgpu::RenderPipeline
{
    let shader_source =
        std::fs::read_to_string("shaders/blit.wgsl").expect("Failed to read blit shader");

    let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
        label: Some("Blit Shader"),
        source: wgpu::ShaderSource::Wgsl(shader_source.into()),
    });

    let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
        label: Some("Blit Pipeline Layout"),
        bind_group_layouts: &[bind_group_layout],
        push_constant_ranges: &[],
    });

    device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
        label: Some("Blit Pipeline"),
        layout: Some(&pipeline_layout),
        vertex: wgpu::VertexState {
            module: &shader,
            entry_point: Some("vs_main"),
            buffers: &[ScreenVertex::desc()],
            compilation_options: Default::default(),
        },
        fragment: Some(wgpu::FragmentState {
            module: &shader,
            entry_point: Some("fs_main"),
            targets: &[Some(wgpu::ColorTargetState {
                format,
                blend: Some(wgpu::BlendState::REPLACE),
                write_mask: wgpu::ColorWrites::ALL,
            })],
            compilation_options: Default::default(),
        }),
        primitive: wgpu::PrimitiveState {
            topology: wgpu::PrimitiveTopology::TriangleList,
            strip_index_format: None,
            front_face: wgpu::FrontFace::Ccw,
            cull_mode: None,
            polygon_mode: wgpu::PolygonMode::Fill,
            unclipped_depth: false,
            conservative: false,
        },
        depth_stencil: None,
        multisample: wgpu::MultisampleState {
            count: 1,
            mask: !0,
            alpha_to_coverage_enabled: false,
        },
        multiview: None,
        cache: None,
    })
}