1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
use std::num::NonZeroU64;

use super::{AlignmentValue, BufferMut, BufferRef, Reader, SizeValue, Writer};

const UNIFORM_MIN_ALIGNMENT: AlignmentValue = AlignmentValue::new(16);

pub struct Metadata<E> {
    pub alignment: AlignmentValue,
    pub has_uniform_min_alignment: bool,
    pub min_size: SizeValue,
    pub is_pod: bool,
    pub extra: E,
}

impl Metadata<()> {
    pub const fn from_alignment_and_size(alignment: u64, size: u64) -> Self {
        Self {
            alignment: AlignmentValue::new(alignment),
            has_uniform_min_alignment: false,
            min_size: SizeValue::new(size),
            is_pod: false,
            extra: (),
        }
    }
}

// using forget() avoids "destructors cannot be evaluated at compile-time" error
// track #![feature(const_precise_live_drops)] (https://github.com/rust-lang/rust/issues/73255)

impl<E> Metadata<E> {
    #[inline]
    pub const fn alignment(self) -> AlignmentValue {
        let value = self.alignment;
        core::mem::forget(self);
        value
    }

    #[inline]
    pub const fn uniform_min_alignment(self) -> Option<AlignmentValue> {
        let value = self.has_uniform_min_alignment;
        core::mem::forget(self);
        match value {
            true => Some(UNIFORM_MIN_ALIGNMENT),
            false => None,
        }
    }

    #[inline]
    pub const fn min_size(self) -> SizeValue {
        let value = self.min_size;
        core::mem::forget(self);
        value
    }

    #[inline]
    pub const fn is_pod(self) -> bool {
        let value = self.is_pod;
        core::mem::forget(self);
        value
    }

    #[inline]
    pub const fn pod(mut self) -> Self {
        self.is_pod = true;
        self
    }

    #[inline]
    pub const fn no_pod(mut self) -> Self {
        self.is_pod = false;
        self
    }
}

/// Base trait for all [WGSL host-shareable types](https://gpuweb.github.io/gpuweb/wgsl/#host-shareable-types)
pub trait ShaderType {
    #[doc(hidden)]
    type ExtraMetadata;
    #[doc(hidden)]
    const METADATA: Metadata<Self::ExtraMetadata>;

    /// Represents the minimum size of `Self` (equivalent to [GPUBufferBindingLayout.minBindingSize](https://gpuweb.github.io/gpuweb/#dom-gpubufferbindinglayout-minbindingsize))
    ///
    /// For [WGSL fixed-footprint types](https://gpuweb.github.io/gpuweb/wgsl/#fixed-footprint-types)
    /// it represents [WGSL Size](https://gpuweb.github.io/gpuweb/wgsl/#alignment-and-size)
    /// (equivalent to [`ShaderSize::SHADER_SIZE`])
    ///
    /// For
    /// [WGSL runtime-sized arrays](https://gpuweb.github.io/gpuweb/wgsl/#runtime-sized) and
    /// [WGSL structs containing runtime-sized arrays](https://gpuweb.github.io/gpuweb/wgsl/#struct-types)
    /// (non fixed-footprint types)
    /// this will be calculated by assuming the array has one element
    #[inline]
    fn min_size() -> NonZeroU64 {
        Self::METADATA.min_size().0
    }

    /// Returns the size of `Self` at runtime
    ///
    /// For [WGSL fixed-footprint types](https://gpuweb.github.io/gpuweb/wgsl/#fixed-footprint-types)
    /// it's equivalent to [`Self::min_size`] and [`ShaderSize::SHADER_SIZE`]
    #[inline]
    fn size(&self) -> NonZeroU64 {
        Self::METADATA.min_size().0
    }

    #[doc(hidden)]
    const UNIFORM_COMPAT_ASSERT: fn() = || {};

    /// Asserts that `Self` meets the requirements of the
    /// [uniform address space restrictions on stored values](https://gpuweb.github.io/gpuweb/wgsl/#address-spaces-uniform) and the
    /// [uniform address space layout constraints](https://gpuweb.github.io/gpuweb/wgsl/#address-space-layout-constraints)
    ///
    /// # Examples
    ///
    /// ## Array
    ///
    /// Will panic since runtime-sized arrays are not compatible with the
    /// uniform address space restrictions on stored values
    ///
    /// ```should_panic
    /// # use crate::encase::ShaderType;
    /// <Vec<mint::Vector4<f32>>>::assert_uniform_compat();
    /// ```
    ///
    /// Will panic since the stride is 4 bytes
    ///
    /// ```should_panic
    /// # use crate::encase::ShaderType;
    /// <[f32; 2]>::assert_uniform_compat();
    /// ```
    ///
    /// Will not panic since the stride is 16 bytes
    ///
    /// ```
    /// # use crate::encase::ShaderType;
    /// # use mint;
    /// <[mint::Vector4<f32>; 2]>::assert_uniform_compat();
    /// ```
    ///
    /// ## Struct
    ///
    /// Will panic since runtime-sized arrays are not compatible with the
    /// uniform address space restrictions on stored values
    ///
    /// ```should_panic
    /// # use crate::encase::ShaderType;
    /// # use mint;
    /// #[derive(ShaderType)]
    /// struct Invalid {
    ///     #[size(runtime)]
    ///     vec: Vec<mint::Vector4<f32>>
    /// }
    /// Invalid::assert_uniform_compat();
    /// ```
    ///
    /// Will panic since the inner struct's size must be a multiple of 16
    ///
    /// ```should_panic
    /// # use crate::encase::ShaderType;
    /// #[derive(ShaderType)]
    /// struct S {
    ///     x: f32,
    /// }
    ///
    /// #[derive(ShaderType)]
    /// struct Invalid {
    ///     a: f32,
    ///     b: S, // offset between fields 'a' and 'b' must be at least 16 (currently: 4)
    /// }
    /// Invalid::assert_uniform_compat();
    /// ```
    ///
    /// Will not panic (fixed via align attribute)
    ///
    /// ```
    /// # use crate::encase::ShaderType;
    /// # #[derive(ShaderType)]
    /// # struct S {
    /// #     x: f32,
    /// # }
    /// #[derive(ShaderType)]
    /// struct Valid {
    ///     a: f32,
    ///     #[align(16)]
    ///     b: S,
    /// }
    /// Valid::assert_uniform_compat();
    /// ```
    ///
    /// Will not panic (fixed via size attribute)
    ///
    /// ```
    /// # use crate::encase::ShaderType;
    /// # #[derive(ShaderType)]
    /// # struct S {
    /// #     x: f32,
    /// # }
    /// #[derive(ShaderType)]
    /// struct Valid {
    ///     #[size(16)]
    ///     a: f32,
    ///     b: S,
    /// }
    /// Valid::assert_uniform_compat();
    /// ```
    #[inline]
    fn assert_uniform_compat() {
        Self::UNIFORM_COMPAT_ASSERT();
    }

    // fn assert_can_write_into()
    // where
    //     Self: WriteInto,
    // {
    // }

    // fn assert_can_read_from()
    // where
    //     Self: ReadFrom,
    // {
    // }

    // fn assert_can_create_from()
    // where
    //     Self: CreateFrom,
    // {
    // }
}

/// Trait implemented for all [WGSL fixed-footprint types](https://gpuweb.github.io/gpuweb/wgsl/#fixed-footprint-types)
pub trait ShaderSize: ShaderType {
    /// Represents [WGSL Size](https://gpuweb.github.io/gpuweb/wgsl/#alignment-and-size) (equivalent to [`ShaderType::min_size`])
    const SHADER_SIZE: NonZeroU64 = Self::METADATA.min_size().0;
}

/// Trait implemented for
/// [WGSL runtime-sized arrays](https://gpuweb.github.io/gpuweb/wgsl/#runtime-sized) and
/// [WGSL structs containing runtime-sized arrays](https://gpuweb.github.io/gpuweb/wgsl/#struct-types)
/// (non fixed-footprint types)
pub trait CalculateSizeFor {
    /// Returns the size of `Self` assuming the (contained) runtime-sized array has `nr_of_el` elements
    fn calculate_size_for(nr_of_el: u64) -> NonZeroU64;
}

#[allow(clippy::len_without_is_empty)]
pub trait RuntimeSizedArray {
    fn len(&self) -> usize;
}

pub trait WriteInto {
    fn write_into<B>(&self, writer: &mut Writer<B>)
    where
        B: BufferMut;
}

pub trait ReadFrom {
    fn read_from<B>(&mut self, reader: &mut Reader<B>)
    where
        B: BufferRef;
}

pub trait CreateFrom: Sized {
    fn create_from<B>(reader: &mut Reader<B>) -> Self
    where
        B: BufferRef;
}