Derive Macro Desc 

#[derive(Desc)]
{
    // Attributes available to this derive:
    #[u8x2]
    #[u8x4]
    #[s8x2]
    #[s8x4]
    #[un8x2]
    #[un8x4]
    #[sn8x2]
    #[sn8x4]
    #[u16x2]
    #[u16x4]
    #[s16x2]
    #[s16x4]
    #[un16x2]
    #[un16x4]
    #[sn16x2]
    #[sn16x4]
    #[f16x2]
    #[f16x4]
    #[f32]
    #[f32x2]
    #[f32x3]
    #[f32x4]
    #[u32]
    #[u32x2]
    #[u32x3]
    #[u32x4]
    #[s32]
    #[s32x2]
    #[s32x3]
    #[s32x4]
    #[f64]
    #[f64x2]
    #[f64x3]
    #[f64x4]
    #[mat2x2]
    #[mat2x3]
    #[mat2x4]
    #[mat3x2]
    #[mat3x3]
    #[mat3x4]
    #[mat4x2]
    #[mat4x3]
    #[mat4x4]
}

Desc is a proc derive macro that allow you to describe a structure as a description to pass to a renderpipeline.

Example

use wrld::Desc;

#[repr(C)]
#[derive(Desc)]
struct Test {
    #[f32x3(0)] position: Vector3
    #[f32x4(1)] color: Vector4
}

into

impl Test {
    pub fn desc<'a>() -> wgpu::VertexBufferLayout<'a> {
        // let size_f32 = size_of::<f32>() = 4
        // let f32x3 = size_f32 * 3 = 12;
        // let f32x4 = size_f32 * 4 = 16;
        // let array_stride = 12 + 16 = 28;
 
        wgpu::VertexBufferLayout {
            array_stride: 28 as wgpu::BufferAddress // array_stride variable,
            step_mode: wgpu::VertexStepMode::Vertex,
            attributes: &[
                wgpu::VertexAttribute {
                    offset: 0u64,
                    format: wgpu::VertexFormat::Float32x3,
                    shader_location: 0u32,
                },
                wgpu::VertexAttribute {
                    offset: 12u64,
                    format: wgpu::VertexFormat::Float32x4,
                    shader_location: 1u32,
                },
            ],
        }
    }
}

Matrice attributes

Matrices attributes are kind of special, because matrices are the only attributes that can take multiple location.

Matrices need two argument :

• The type of the matrice (u8, f32, f64, ect…)
• And the starting location

Matrices dimension start from 2x2 to 4x4

Example

#[repr(C)]
#[derive(wrld::Desc)]
struct Actor {
    #[mat4x2(u8, 0)] transform: [[f32; 4]; 4]
}

Will result to

impl Actor {
    pub fn desc<'a>() -> wgpu::VertexBufferLayout<'a> {
        wgpu::VertexBufferLayout {
            array_stride: 8u64 as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Instance,
            attributes: &[
                wgpu::VertexAttribute {
                    offset: 0u64,
                    format: wgpu::VertexFormat::Uint8x2,
                    shader_location: 0u32,
                },
                wgpu::VertexAttribute {
                    offset: 2u64,
                    format: wgpu::VertexFormat::Uint8x2,
                    shader_location: 1u32,
                },
                wgpu::VertexAttribute {
                    offset: 4u64,
                    format: wgpu::VertexFormat::Uint8x2,
                    shader_location: 2u32,
                },
                wgpu::VertexAttribute {
                    offset: 6u64,
                    format: wgpu::VertexFormat::Uint8x2,
                    shader_location: 3u32,
                },
            ],
        }
    }
}

So take care while using it.

Also matrix type handle only wgpu VertexFormat type for row. That does mean that matrix like that.

#[repr(C)]
#[derive(wrld::DescInstance)]
struct Vertex {
    #[mat4x3(u8, 0)] transform: [[f32; 4]; 4]
}

Will throw an error :

“Matrix mat4x3 cannot be use with u8 ! Available matrix are mat4x2 or mat4x4 for u8”

Thing to know

• Desc will not handle data transformation
• Desc does not handle chaotic structure