[spv-in] add a flag to adjust the coordinate space

bin/convert.rs

@@ -5,6 +5,8 @@ use std::{env, error::Error, path::Path};
 
 #[derive(Default)]
 struct Parameters {
+    #[cfg(feature = "spv-in")]
+    spv_adjust_coordinate_space: bool,
     #[cfg(feature = "spv-in")]
     spv_flow_dump_prefix: Option<String>,
     #[cfg(feature = "spv-out")]
@@ -102,6 +104,7 @@ fn main() {
         #[cfg(feature = "spv-in")]
         "spv" => {
             let options = naga::front::spv::Options {
+                adjust_coordinate_space: params.spv_adjust_coordinate_space,
                 flow_graph_dump_prefix: params.spv_flow_dump_prefix.map(std::path::PathBuf::from),
             };
             let input = fs::read(input_path).unwrap();

src/front/spv/function.rs

@@ -279,31 +279,34 @@ impl<I: Iterator<Item = u32>> super::Parser<I> {
                 }
             }
 
-            let position_index = members.iter().position(|member| match member.binding {
-                Some(crate::Binding::BuiltIn(crate::BuiltIn::Position)) => true,
-                _ => false,
-            });
-            if let Some(component_index) = position_index {
-                let old_len = function.expressions.len();
-                let global_expr = components[component_index];
-                let access_expr = function.expressions.append(crate::Expression::AccessIndex {
-                    base: global_expr,
-                    index: 1,
-                });
-                let load_expr = function.expressions.append(crate::Expression::Load {
-                    pointer: access_expr,
-                });
-                let neg_expr = function.expressions.append(crate::Expression::Unary {
-                    op: crate::UnaryOperator::Negate,
-                    expr: load_expr,
-                });
-                function.body.push(crate::Statement::Emit(
-                    function.expressions.range_from(old_len),
-                ));
-                function.body.push(crate::Statement::Store {
-                    pointer: access_expr,
-                    value: neg_expr,
+            if self.options.adjust_coordinate_space {
+                let position_index = members.iter().position(|member| match member.binding {
+                    Some(crate::Binding::BuiltIn(crate::BuiltIn::Position)) => true,
+                    _ => false,
                 });
+                if let Some(component_index) = position_index {
+                    // The IR is Y-up, while SPIR-V is Y-down.
+                    let old_len = function.expressions.len();
+                    let global_expr = components[component_index];
+                    let access_expr = function.expressions.append(crate::Expression::AccessIndex {
+                        base: global_expr,
+                        index: 1,
+                    });
+                    let load_expr = function.expressions.append(crate::Expression::Load {
+                        pointer: access_expr,
+                    });
+                    let neg_expr = function.expressions.append(crate::Expression::Unary {
+                        op: crate::UnaryOperator::Negate,
+                        expr: load_expr,
+                    });
+                    function.body.push(crate::Statement::Emit(
+                        function.expressions.range_from(old_len),
+                    ));
+                    function.body.push(crate::Statement::Store {
+                        pointer: access_expr,
+                        value: neg_expr,
+                    });
+                }
             }
 
             let old_len = function.expressions.len();

src/front/spv/mod.rs

@@ -312,11 +312,24 @@ enum ExtendedClass {
     Output,
 }
 
-#[derive(Clone, Debug, Default)]
+#[derive(Clone, Debug)]
 pub struct Options {
+    /// The IR coordinate space matches all the APIs except SPIR-V,
+    /// so by default we flip the Y coordinate of the `BuiltIn::Position`.
+    /// This flag can be used to avoid this.
+    pub adjust_coordinate_space: bool,
     pub flow_graph_dump_prefix: Option<PathBuf>,
 }
 
+impl Default for Options {
+    fn default() -> Self {
+        Options {
+            adjust_coordinate_space: true,
+            flow_graph_dump_prefix: None,
+        }
+    }
+}
+
 pub struct Parser<I> {
     data: I,
     state: ModuleState,

tests/out/quad-vert.msl.snap

@@ -69,7 +69,6 @@ vertex main2Output main2(
     a_uv = a_uv1;
     a_pos = a_pos1;
     main1(v_uv, a_uv, _, a_pos);
-    _.gl_Position.y = -_.gl_Position.y;
     const auto _tmp = type10 {v_uv, _.gl_Position, _.gl_PointSize, {_.gl_ClipDistance[0]}};
     return main2Output { _tmp.member, _tmp.gl_Position1, _tmp.gl_PointSize1, {_tmp.gl_ClipDistance1[0]} };
 }

tests/snapshots.rs

@@ -279,10 +279,13 @@ fn convert_wgsl_texture_array() {
 }
 
 #[cfg(feature = "spv-in")]
-fn convert_spv(name: &str, targets: Targets) {
+fn convert_spv(name: &str, adjust_coordinate_space: bool, targets: Targets) {
     let module = naga::front::spv::parse_u8_slice(
         &std::fs::read(format!("tests/in/{}{}", name, ".spv")).expect("Couldn't find spv file"),
-        &Default::default(),
+        &naga::front::spv::Options {
+            adjust_coordinate_space,
+            flow_graph_dump_prefix: None,
+        },
     )
     .unwrap();
     check_targets(&module, name, targets);
@@ -294,13 +297,13 @@ fn convert_spv(name: &str, targets: Targets) {
 #[cfg(feature = "spv-in")]
 #[test]
 fn convert_spv_quad_vert() {
-    convert_spv("quad-vert", Targets::METAL);
+    convert_spv("quad-vert", false, Targets::METAL);
 }
 
 #[cfg(feature = "spv-in")]
 #[test]
 fn convert_spv_shadow() {
-    convert_spv("shadow", Targets::IR | Targets::ANALYSIS);
+    convert_spv("shadow", true, Targets::IR | Targets::ANALYSIS);
 }
 
 #[cfg(feature = "glsl-in")]