pub enum BoundsCheckPolicy {
    Restrict,
    ReadZeroSkipWrite,
    Unchecked,
}
Expand description

How should code generated by Naga do bounds checks?

When a vector, matrix, or array index is out of bounds—either negative, or greater than or equal to the number of elements in the type—WGSL requires that some other index of the implementation’s choice that is in bounds is used instead. (There are no types with zero elements.)

Similarly, when out-of-bounds coordinates, array indices, or sample indices are presented to the WGSL textureLoad and textureStore operations, the operation is redirected to do something safe.

Different users of Naga will prefer different defaults:

  • When used as part of a WebGPU implementation, the WGSL specification requires the Restrict behavior for array, vector, and matrix accesses, and either the Restrict or ReadZeroSkipWrite behaviors for texture accesses.

  • When used by the wgpu crate for native development, wgpu selects ReadZeroSkipWrite as its default.

  • Naga’s own default is Unchecked, so that shader translations are as faithful to the original as possible.

Sometimes the underlying hardware and drivers can perform bounds checks themselves, in a way that performs better than the checks Naga would inject. If you’re using native checks like this, then having Naga inject its own checks as well would be redundant, and the Unchecked policy is appropriate.

Variants§

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Restrict

Replace out-of-bounds indexes with some arbitrary in-bounds index.

(This does not necessarily mean clamping. For example, interpreting the index as unsigned and taking the minimum with the largest valid index would also be a valid implementation. That would map negative indices to the last element, not the first.)

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ReadZeroSkipWrite

Out-of-bounds reads return zero, and writes have no effect.

When applied to a chain of accesses, like a[i][j].b[k], all index expressions are evaluated, regardless of whether prior or later index expressions were in bounds. But all the accesses per se are skipped if any index is out of bounds.

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Unchecked

Naga adds no checks to indexing operations. Generate the fastest code possible. This is the default for Naga, as a translator, but consumers should consider defaulting to a safer behavior.

Trait Implementations§

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impl Clone for BoundsCheckPolicy

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fn clone(&self) -> BoundsCheckPolicy

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for BoundsCheckPolicy

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl Default for BoundsCheckPolicy

The default BoundsCheckPolicy is Unchecked.

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fn default() -> Self

Returns the “default value” for a type. Read more
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impl Hash for BoundsCheckPolicy

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fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl PartialEq for BoundsCheckPolicy

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fn eq(&self, other: &BoundsCheckPolicy) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl Copy for BoundsCheckPolicy

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impl Eq for BoundsCheckPolicy

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impl StructuralEq for BoundsCheckPolicy

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impl StructuralPartialEq for BoundsCheckPolicy

Auto Trait Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.