1 files changed, 61 insertions, 0 deletions
diff --git a/third_party/rust/naga/src/front/interpolator.rs b/third_party/rust/naga/src/front/interpolator.rs
new file mode 100644
index 0000000000..96f5db6ff7
--- /dev/null
+++ b/third_party/rust/naga/src/front/interpolator.rs
@@ -0,0 +1,61 @@
+/*!
+Interpolation defaults.
+*/
+
+impl crate::Binding {
+    /// Apply the usual default interpolation for `ty` to `binding`.
+    ///
+    /// This function is a utility front ends may use to satisfy the Naga IR's
+    /// requirement, meant to ensure that input languages' policies have been
+    /// applied appropriately, that all I/O `Binding`s from the vertex shader to the
+    /// fragment shader must have non-`None` `interpolation` values.
+    ///
+    /// All the shader languages Naga supports have similar rules:
+    /// perspective-correct, center-sampled interpolation is the default for any
+    /// binding that can vary, and everything else either defaults to flat, or
+    /// requires an explicit flat qualifier/attribute/what-have-you.
+    ///
+    /// If `binding` is not a [`Location`] binding, or if its [`interpolation`] is
+    /// already set, then make no changes. Otherwise, set `binding`'s interpolation
+    /// and sampling to reasonable defaults depending on `ty`, the type of the value
+    /// being interpolated:
+    ///
+    /// - If `ty` is a floating-point scalar, vector, or matrix type, then
+    ///   default to [`Perspective`] interpolation and [`Center`] sampling.
+    ///
+    /// - If `ty` is an integral scalar or vector, then default to [`Flat`]
+    ///   interpolation, which has no associated sampling.
+    ///
+    /// - For any other types, make no change. Such types are not permitted as
+    ///   user-defined IO values, and will probably be flagged by the verifier
+    ///
+    /// When structs appear in input or output types, each member ought to have its
+    /// own [`Binding`], so structs are simply covered by the third case.
+    ///
+    /// [`Binding`]: crate::Binding
+    /// [`Location`]: crate::Binding::Location
+    /// [`interpolation`]: crate::Binding::Location::interpolation
+    /// [`Perspective`]: crate::Interpolation::Perspective
+    /// [`Flat`]: crate::Interpolation::Flat
+    /// [`Center`]: crate::Sampling::Center
+    pub fn apply_default_interpolation(&mut self, ty: &crate::TypeInner) {
+        if let crate::Binding::Location {
+            location: _,
+            interpolation: ref mut interpolation @ None,
+            ref mut sampling,
+        } = *self
+        {
+            match ty.scalar_kind() {
+                Some(crate::ScalarKind::Float) => {
+                    *interpolation = Some(crate::Interpolation::Perspective);
+                    *sampling = Some(crate::Sampling::Center);
+                }
+                Some(crate::ScalarKind::Sint | crate::ScalarKind::Uint) => {
+                    *interpolation = Some(crate::Interpolation::Flat);
+                    *sampling = None;
+                }
+                Some(_) | None => {}
+            }
+        }
+    }
+}