naga/proc/
layouter.rs

1use crate::arena::{Handle, HandleVec};
2use std::{fmt::Display, num::NonZeroU32, ops};
3
4/// A newtype struct where its only valid values are powers of 2
5#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
6#[cfg_attr(feature = "serialize", derive(serde::Serialize))]
7#[cfg_attr(feature = "deserialize", derive(serde::Deserialize))]
8pub struct Alignment(NonZeroU32);
9
10impl Alignment {
11    pub const ONE: Self = Self(unsafe { NonZeroU32::new_unchecked(1) });
12    pub const TWO: Self = Self(unsafe { NonZeroU32::new_unchecked(2) });
13    pub const FOUR: Self = Self(unsafe { NonZeroU32::new_unchecked(4) });
14    pub const EIGHT: Self = Self(unsafe { NonZeroU32::new_unchecked(8) });
15    pub const SIXTEEN: Self = Self(unsafe { NonZeroU32::new_unchecked(16) });
16
17    pub const MIN_UNIFORM: Self = Self::SIXTEEN;
18
19    pub const fn new(n: u32) -> Option<Self> {
20        if n.is_power_of_two() {
21            // SAFETY: value can't be 0 since we just checked if it's a power of 2
22            Some(Self(unsafe { NonZeroU32::new_unchecked(n) }))
23        } else {
24            None
25        }
26    }
27
28    /// # Panics
29    /// If `width` is not a power of 2
30    pub fn from_width(width: u8) -> Self {
31        Self::new(width as u32).unwrap()
32    }
33
34    /// Returns whether or not `n` is a multiple of this alignment.
35    pub const fn is_aligned(&self, n: u32) -> bool {
36        // equivalent to: `n % self.0.get() == 0` but much faster
37        n & (self.0.get() - 1) == 0
38    }
39
40    /// Round `n` up to the nearest alignment boundary.
41    pub const fn round_up(&self, n: u32) -> u32 {
42        // equivalent to:
43        // match n % self.0.get() {
44        //     0 => n,
45        //     rem => n + (self.0.get() - rem),
46        // }
47        let mask = self.0.get() - 1;
48        (n + mask) & !mask
49    }
50}
51
52impl Display for Alignment {
53    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
54        self.0.get().fmt(f)
55    }
56}
57
58impl ops::Mul<u32> for Alignment {
59    type Output = u32;
60
61    fn mul(self, rhs: u32) -> Self::Output {
62        self.0.get() * rhs
63    }
64}
65
66impl ops::Mul for Alignment {
67    type Output = Alignment;
68
69    fn mul(self, rhs: Alignment) -> Self::Output {
70        // SAFETY: both lhs and rhs are powers of 2, the result will be a power of 2
71        Self(unsafe { NonZeroU32::new_unchecked(self.0.get() * rhs.0.get()) })
72    }
73}
74
75impl From<crate::VectorSize> for Alignment {
76    fn from(size: crate::VectorSize) -> Self {
77        match size {
78            crate::VectorSize::Bi => Alignment::TWO,
79            crate::VectorSize::Tri => Alignment::FOUR,
80            crate::VectorSize::Quad => Alignment::FOUR,
81        }
82    }
83}
84
85/// Size and alignment information for a type.
86#[derive(Clone, Copy, Debug, Hash, PartialEq)]
87#[cfg_attr(feature = "serialize", derive(serde::Serialize))]
88#[cfg_attr(feature = "deserialize", derive(serde::Deserialize))]
89pub struct TypeLayout {
90    pub size: u32,
91    pub alignment: Alignment,
92}
93
94impl TypeLayout {
95    /// Produce the stride as if this type is a base of an array.
96    pub const fn to_stride(&self) -> u32 {
97        self.alignment.round_up(self.size)
98    }
99}
100
101/// Helper processor that derives the sizes of all types.
102///
103/// `Layouter` uses the default layout algorithm/table, described in
104/// [WGSL §4.3.7, "Memory Layout"]
105///
106/// A `Layouter` may be indexed by `Handle<Type>` values: `layouter[handle]` is the
107/// layout of the type whose handle is `handle`.
108///
109/// [WGSL §4.3.7, "Memory Layout"](https://gpuweb.github.io/gpuweb/wgsl/#memory-layouts)
110#[derive(Debug, Default)]
111pub struct Layouter {
112    /// Layouts for types in an arena.
113    layouts: HandleVec<crate::Type, TypeLayout>,
114}
115
116impl ops::Index<Handle<crate::Type>> for Layouter {
117    type Output = TypeLayout;
118    fn index(&self, handle: Handle<crate::Type>) -> &TypeLayout {
119        &self.layouts[handle]
120    }
121}
122
123#[derive(Clone, Copy, Debug, PartialEq, thiserror::Error)]
124pub enum LayoutErrorInner {
125    #[error("Array element type {0:?} doesn't exist")]
126    InvalidArrayElementType(Handle<crate::Type>),
127    #[error("Struct member[{0}] type {1:?} doesn't exist")]
128    InvalidStructMemberType(u32, Handle<crate::Type>),
129    #[error("Type width must be a power of two")]
130    NonPowerOfTwoWidth,
131}
132
133#[derive(Clone, Copy, Debug, PartialEq, thiserror::Error)]
134#[error("Error laying out type {ty:?}: {inner}")]
135pub struct LayoutError {
136    pub ty: Handle<crate::Type>,
137    pub inner: LayoutErrorInner,
138}
139
140impl LayoutErrorInner {
141    const fn with(self, ty: Handle<crate::Type>) -> LayoutError {
142        LayoutError { ty, inner: self }
143    }
144}
145
146impl Layouter {
147    /// Remove all entries from this `Layouter`, retaining storage.
148    pub fn clear(&mut self) {
149        self.layouts.clear();
150    }
151
152    /// Extend this `Layouter` with layouts for any new entries in `gctx.types`.
153    ///
154    /// Ensure that every type in `gctx.types` has a corresponding [TypeLayout]
155    /// in [`self.layouts`].
156    ///
157    /// Some front ends need to be able to compute layouts for existing types
158    /// while module construction is still in progress and new types are still
159    /// being added. This function assumes that the `TypeLayout` values already
160    /// present in `self.layouts` cover their corresponding entries in `types`,
161    /// and extends `self.layouts` as needed to cover the rest. Thus, a front
162    /// end can call this function at any time, passing its current type and
163    /// constant arenas, and then assume that layouts are available for all
164    /// types.
165    #[allow(clippy::or_fun_call)]
166    pub fn update(&mut self, gctx: super::GlobalCtx) -> Result<(), LayoutError> {
167        use crate::TypeInner as Ti;
168
169        for (ty_handle, ty) in gctx.types.iter().skip(self.layouts.len()) {
170            let size = ty.inner.size(gctx);
171            let layout = match ty.inner {
172                Ti::Scalar(scalar) | Ti::Atomic(scalar) => {
173                    let alignment = Alignment::new(scalar.width as u32)
174                        .ok_or(LayoutErrorInner::NonPowerOfTwoWidth.with(ty_handle))?;
175                    TypeLayout { size, alignment }
176                }
177                Ti::Vector {
178                    size: vec_size,
179                    scalar,
180                } => {
181                    let alignment = Alignment::new(scalar.width as u32)
182                        .ok_or(LayoutErrorInner::NonPowerOfTwoWidth.with(ty_handle))?;
183                    TypeLayout {
184                        size,
185                        alignment: Alignment::from(vec_size) * alignment,
186                    }
187                }
188                Ti::Matrix {
189                    columns: _,
190                    rows,
191                    scalar,
192                } => {
193                    let alignment = Alignment::new(scalar.width as u32)
194                        .ok_or(LayoutErrorInner::NonPowerOfTwoWidth.with(ty_handle))?;
195                    TypeLayout {
196                        size,
197                        alignment: Alignment::from(rows) * alignment,
198                    }
199                }
200                Ti::Pointer { .. } | Ti::ValuePointer { .. } => TypeLayout {
201                    size,
202                    alignment: Alignment::ONE,
203                },
204                Ti::Array {
205                    base,
206                    stride: _,
207                    size: _,
208                } => TypeLayout {
209                    size,
210                    alignment: if base < ty_handle {
211                        self[base].alignment
212                    } else {
213                        return Err(LayoutErrorInner::InvalidArrayElementType(base).with(ty_handle));
214                    },
215                },
216                Ti::Struct { span, ref members } => {
217                    let mut alignment = Alignment::ONE;
218                    for (index, member) in members.iter().enumerate() {
219                        alignment = if member.ty < ty_handle {
220                            alignment.max(self[member.ty].alignment)
221                        } else {
222                            return Err(LayoutErrorInner::InvalidStructMemberType(
223                                index as u32,
224                                member.ty,
225                            )
226                            .with(ty_handle));
227                        };
228                    }
229                    TypeLayout {
230                        size: span,
231                        alignment,
232                    }
233                }
234                Ti::Image { .. }
235                | Ti::Sampler { .. }
236                | Ti::AccelerationStructure
237                | Ti::RayQuery
238                | Ti::BindingArray { .. } => TypeLayout {
239                    size,
240                    alignment: Alignment::ONE,
241                },
242            };
243            debug_assert!(size <= layout.size);
244            self.layouts.insert(ty_handle, layout);
245        }
246
247        Ok(())
248    }
249}
naga/proc/layouter.rs

naga/proc/
layouter.rs
