Make "None" interpolation mean default or nothing, depending on context (gfx-rs#146)

* Make no interpolation mean default or nothing, depending on context

* Re-add Interpolation::Perspective

Author: lachlansneff

src/front/glsl/mod.rs

@@ -1174,7 +1174,7 @@ impl<'a> Parser<'a> {
     ) -> (StorageClass, Option<Binding>, Option<Interpolation>) {
         let mut storage = None;
         let mut binding = None;
-        let mut interpolation = Interpolation::Perspective;
+        let mut interpolation = None;
 
         for qualifier in qualifier.qualifiers {
             match qualifier {
@@ -1243,25 +1243,20 @@ impl<'a> Parser<'a> {
                     }
                 }
                 TypeQualifierSpec::Interpolation(interpolation_qualifier) => {
-                    interpolation = match interpolation_qualifier {
+                    interpolation = Some(match interpolation_qualifier {
                         InterpolationQualifier::NoPerspective => Interpolation::Linear,
                         InterpolationQualifier::Flat => Interpolation::Flat,
                         InterpolationQualifier::Smooth => Interpolation::Perspective,
-                    }
+                    });
                 }
                 _ => unimplemented!(),
             }
         }
 
-        let class = storage.unwrap_or(StorageClass::Private);
-
         (
-            class,
+            storage.unwrap_or(StorageClass::Private),
             binding,
-            match class {
-                StorageClass::Input | StorageClass::Output => Some(interpolation),
-                _ => None,
-            },
+            interpolation,
         )
     }
 }

src/front/glsl_new/parser.rs

@@ -743,11 +743,6 @@ pomelo! {
 
         let interpolation = d.type_qualifiers.iter().find_map(|tq| {
             if let TypeQualifier::Interpolation(i) = tq { Some(*i) } else { None }
-        }).or_else(|| match class {
-            StorageClass::Input | StorageClass::Output => {
-                Some(Interpolation::Perspective)
-            }
-            _ => None,
         });
 
         for (id, initializer) in d.ids_initializers {

src/front/spv.rs

@@ -2008,12 +2008,7 @@ impl<I: Iterator<Item = u32>> Parser<I> {
             class,
             binding,
             ty,
-            interpolation: dec.interpolation.or_else(|| match class {
-                crate::StorageClass::Input | crate::StorageClass::Output => {
-                    Some(crate::Interpolation::Perspective)
-                }
-                _ => None,
-            }),
+            interpolation: dec.interpolation,
         };
         self.lookup_variable.insert(
             id,

src/front/wgsl.rs

@@ -508,6 +508,7 @@ impl Parser {
             "flat" => Ok(crate::Interpolation::Flat),
             "centroid" => Ok(crate::Interpolation::Centroid),
             "sample" => Ok(crate::Interpolation::Sample),
+            "perspective" => Ok(crate::Interpolation::Perspective),
             _ => Err(Error::UnknownDecoration(word)),
         }
     }
@@ -1557,7 +1558,7 @@ impl Parser {
         // read decorations
         let mut binding = None;
         // Perspective is the default qualifier.
-        let mut interpolation = crate::Interpolation::Perspective;
+        let mut interpolation = None;
         if lexer.skip(Token::DoubleParen('[')) {
             let (mut bind_index, mut bind_set) = (None, None);
             self.scopes.push(Scope::Decoration);
@@ -1578,7 +1579,10 @@ impl Parser {
                         bind_set = Some(lexer.next_uint_literal()?);
                     }
                     "interpolate" => {
-                        interpolation = Self::get_interpolation(lexer.next_ident()?)?;
+                        if interpolation.is_some() {
+                            return Err(Error::UnknownDecoration(lexer.next_ident()?));
+                        }
+                        interpolation = Some(Self::get_interpolation(lexer.next_ident()?)?);
                     }
                     word => return Err(Error::UnknownDecoration(word)),
                 }
@@ -1667,12 +1671,7 @@ impl Parser {
                     class,
                     binding: binding.take(),
                     ty,
-                    interpolation: match class {
-                        crate::StorageClass::Input | crate::StorageClass::Output => {
-                            Some(interpolation)
-                        }
-                        _ => None,
-                    },
+                    interpolation,
                 });
                 lookup_global_expression
                     .insert(name, crate::Expression::GlobalVariable(var_handle));

src/lib.rs

@@ -341,8 +341,9 @@ pub struct GlobalVariable {
     /// The type of this variable.
     pub ty: Handle<Type>,
     /// The interpolation qualifier, if any.
-    /// Required for global outputs in vertex shaders
-    /// and global inputs in fragment shaders.
+    /// If the this `GlobalVariable` is a vertex output
+    /// or fragment input, `None` corresponds to the
+    /// `smooth`/`perspective` interpolation qualifier.
     pub interpolation: Option<Interpolation>,
 }