[spv-out] option to clamp frag_depth

gfx-rs · Sep 27, 2021 · 1153bc6 · 1153bc6
1 parent aa08cf9
commit 1153bc6
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Showing 5 changed files with 105 additions and 40 deletions.
diff --git a/src/back/spv/block.rs b/src/back/spv/block.rs
@@ -20,6 +20,85 @@ fn get_dimension(type_inner: &crate::TypeInner) -> Dimension {
 }
 
 impl Writer {
+    // Flip Y coordinate to adjust for coordinate space difference
+    // between SPIR-V and our IR.
+    fn write_epilogue_position_y_flip(
+        &mut self,
+        position_id: Word,
+        body: &mut Vec<Instruction>,
+    ) -> Result<(), Error> {
+        let access_id = self.id_gen.next();
+        let float_ptr_type_id = self.get_type_id(LookupType::Local(LocalType::Value {
+            vector_size: None,
+            kind: crate::ScalarKind::Float,
+            width: 4,
+            pointer_class: Some(spirv::StorageClass::Output),
+        }));
+        let index_y_id = self.get_index_constant(1);
+        body.push(Instruction::access_chain(
+            float_ptr_type_id,
+            access_id,
+            position_id,
+            &[index_y_id],
+        ));
+
+        let load_id = self.id_gen.next();
+        let float_type_id = self.get_type_id(LookupType::Local(LocalType::Value {
+            vector_size: None,
+            kind: crate::ScalarKind::Float,
+            width: 4,
+            pointer_class: None,
+        }));
+        body.push(Instruction::load(float_type_id, load_id, access_id, None));
+
+        let neg_id = self.id_gen.next();
+        body.push(Instruction::unary(
+            spirv::Op::FNegate,
+            float_type_id,
+            neg_id,
+            load_id,
+        ));
+
+        body.push(Instruction::store(access_id, neg_id, None));
+        Ok(())
+    }
+
+    // Clamp fragment depth between 0 and 1.
+    fn write_epilogue_frag_depth_clamp(
+        &mut self,
+        frag_depth_id: Word,
+        body: &mut Vec<Instruction>,
+    ) -> Result<(), Error> {
+        let float_type_id = self.get_type_id(LookupType::Local(LocalType::Value {
+            vector_size: None,
+            kind: crate::ScalarKind::Float,
+            width: 4,
+            pointer_class: None,
+        }));
+        let value0_id = self.get_constant_scalar(crate::ScalarValue::Float(0.0), 4);
+        let value1_id = self.get_constant_scalar(crate::ScalarValue::Float(1.0), 4);
+
+        let original_id = self.id_gen.next();
+        body.push(Instruction::load(
+            float_type_id,
+            original_id,
+            frag_depth_id,
+            None,
+        ));
+
+        let clamp_id = self.id_gen.next();
+        body.push(Instruction::ext_inst(
+            self.gl450_ext_inst_id,
+            spirv::GLOp::FClamp,
+            float_type_id,
+            clamp_id,
+            &[original_id, value0_id, value1_id],
+        ));
+
+        body.push(Instruction::store(frag_depth_id, clamp_id, None));
+        Ok(())
+    }
+
     fn write_entry_point_return(
         &mut self,
         value_id: Word,
@@ -44,43 +123,15 @@ impl Writer {
 
             body.push(Instruction::store(res_member.id, member_value_id, None));
 
-            // Flip Y coordinate to adjust for coordinate space difference
-            // between SPIR-V and our IR.
             if self.flags.contains(WriterFlags::ADJUST_COORDINATE_SPACE)
                 && res_member.built_in == Some(crate::BuiltIn::Position)
             {
-                let access_id = self.id_gen.next();
-                let float_ptr_type_id = self.get_type_id(LookupType::Local(LocalType::Value {
-                    vector_size: None,
-                    kind: crate::ScalarKind::Float,
-                    width: 4,
-                    pointer_class: Some(spirv::StorageClass::Output),
-                }));
-                let index_y_id = self.get_index_constant(1);
-                body.push(Instruction::access_chain(
-                    float_ptr_type_id,
-                    access_id,
-                    res_member.id,
-                    &[index_y_id],
-                ));
-
-                let load_id = self.id_gen.next();
-                let float_type_id = self.get_type_id(LookupType::Local(LocalType::Value {
-                    vector_size: None,
-                    kind: crate::ScalarKind::Float,
-                    width: 4,
-                    pointer_class: None,
-                }));
-                body.push(Instruction::load(float_type_id, load_id, access_id, None));
-
-                let neg_id = self.id_gen.next();
-                body.push(Instruction::unary(
-                    spirv::Op::FNegate,
-                    float_type_id,
-                    neg_id,
-                    load_id,
-                ));
-                body.push(Instruction::store(access_id, neg_id, None));
+                self.write_epilogue_position_y_flip(res_member.id, body)?;
+            }
+            if self.flags.contains(WriterFlags::CLAMP_FRAG_DEPTH)
+                && res_member.built_in == Some(crate::BuiltIn::FragDepth)
+            {
+                self.write_epilogue_frag_depth_clamp(res_member.id, body)?;
             }
         }
         Ok(())

diff --git a/src/back/spv/mod.rs b/src/back/spv/mod.rs
@@ -568,6 +568,8 @@ bitflags::bitflags! {
         /// Emit `PointSize` output builtin to vertex shaders, which is
         /// required for drawing with `PointList` topology.
         const FORCE_POINT_SIZE = 0x8;
+        /// Clamp `BuiltIn::FragDepth` output between 0 and 1.
+        const CLAMP_FRAG_DEPTH = 0x10;
     }
 }
 
@@ -592,7 +594,9 @@ pub struct Options {
 
 impl Default for Options {
     fn default() -> Self {
-        let mut flags = WriterFlags::ADJUST_COORDINATE_SPACE | WriterFlags::LABEL_VARYINGS;
+        let mut flags = WriterFlags::ADJUST_COORDINATE_SPACE
+            | WriterFlags::LABEL_VARYINGS
+            | WriterFlags::CLAMP_FRAG_DEPTH;
         if cfg!(debug_assertions) {
             flags |= WriterFlags::DEBUG;
         }

diff --git a/tests/in/interface.param.ron b/tests/in/interface.param.ron
@@ -4,6 +4,7 @@
 		capabilities: [ Shader, SampleRateShading ],
 		adjust_coordinate_space: false,
 		force_point_size: true,
+		clamp_frag_depth: true,
 		separate_entry_points: true,
 	),
 	hlsl_custom: true,

diff --git a/tests/out/spv/interface.fragment.spvasm b/tests/out/spv/interface.fragment.spvasm
@@ -1,7 +1,7 @@
 ; SPIR-V
 ; Version: 1.0
 ; Generator: rspirv
-; Bound: 49
+; Bound: 51
 OpCapability Shader
 OpCapability SampleRateShading
 %1 = OpExtInstImport "GLSL.std.450"
@@ -70,9 +70,12 @@ OpBranch %40
 %45 = OpCompositeConstruct  %13  %44 %42 %43
 %46 = OpCompositeExtract  %4  %45 0
 OpStore %33 %46
-%47 = OpCompositeExtract  %6  %45 1
-OpStore %35 %47
-%48 = OpCompositeExtract  %4  %45 2
-OpStore %37 %48
+%47 = OpLoad  %4  %33
+%48 = OpExtInst  %4  %1 FClamp %47 %7 %3
+OpStore %33 %48
+%49 = OpCompositeExtract  %6  %45 1
+OpStore %35 %49
+%50 = OpCompositeExtract  %4  %45 2
+OpStore %37 %50
 OpReturn
 OpFunctionEnd
diff --git a/tests/snapshots.rs b/tests/snapshots.rs
@@ -62,6 +62,8 @@ struct SpirvOutParameters {
     #[serde(default)]
     force_point_size: bool,
     #[serde(default)]
+    clamp_frag_depth: bool,
+    #[serde(default)]
     separate_entry_points: bool,
 }
 
@@ -201,6 +203,10 @@ fn write_output_spv(
         spv::WriterFlags::FORCE_POINT_SIZE,
         params.spv.force_point_size,
     );
+    flags.set(
+        spv::WriterFlags::CLAMP_FRAG_DEPTH,
+        params.spv.clamp_frag_depth,
+    );
     let options = spv::Options {
         lang_version: (params.spv.version.0, params.spv.version.1),
         flags,