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use pill_engine::internal::{ MeshData, MeshVertex };

use wgpu::util::DeviceExt;
use anyhow::*;

// --- Vertex ---

pub trait Vertex {
    // Defines how a data is layed out in memory (To specify how RenderPipeline needs to map the buffer in the shader)
    fn data_layout_descriptor<'a>() -> wgpu::VertexBufferLayout<'a>;
}

// --- Mesh ---

pub struct RendererMesh {
    pub vertex_buffer: wgpu::Buffer,
    pub index_buffer: wgpu::Buffer,
    pub index_count: u32,
}

impl RendererMesh {
    pub fn new(device: &wgpu::Device, name: &str, mesh_data: &MeshData) -> Result<Self> { 

        let vertex_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some(&format!("{:?}_vertex_buffer", name)),
            contents: bytemuck::cast_slice(&mesh_data.vertices),
            usage: wgpu::BufferUsages::VERTEX,
        });

        let index_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some(&format!("{:?}_vertex_buffer", name)),
            contents: bytemuck::cast_slice(&mesh_data.indices),
            usage: wgpu::BufferUsages::INDEX,
        });

        let renderer_mesh = Self {
            vertex_buffer,
            index_buffer,
            index_count: mesh_data.indices.len() as u32,
        };

        Ok(renderer_mesh)
    }
}

impl Vertex for RendererMesh {
    fn data_layout_descriptor<'a>() -> wgpu::VertexBufferLayout<'a> {
        use std::mem;
        wgpu::VertexBufferLayout {
            array_stride: mem::size_of::<MeshVertex>() as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Vertex,
            attributes: &[
                wgpu::VertexAttribute { // Vertex position
                    offset: 0,  
                    shader_location: 0, 
                    format: wgpu::VertexFormat::Float32x3, 
                },
                wgpu::VertexAttribute { // Vertex texture coordinates
                    offset: mem::size_of::<[f32; 3]>() as wgpu::BufferAddress,
                    shader_location: 1,
                    format: wgpu::VertexFormat::Float32x2,
                },
                wgpu::VertexAttribute { // Vertex normal
                    offset: mem::size_of::<[f32; 5]>() as wgpu::BufferAddress,
                    shader_location: 2,
                    format: wgpu::VertexFormat::Float32x3,
                },
                wgpu::VertexAttribute { // Vertex tangent
                    offset: mem::size_of::<[f32; 8]>() as wgpu::BufferAddress,
                    shader_location: 3,
                    format: wgpu::VertexFormat::Float32x3,
                },
                wgpu::VertexAttribute { // Vertex bitangent
                    offset: mem::size_of::<[f32; 11]>() as wgpu::BufferAddress,
                    shader_location: 4,
                    format: wgpu::VertexFormat::Float32x3,
                },
            ],
        }
    }
}