From 4fb82bd9554d1aa4d9eb4d8a17723f62bbc5457e Mon Sep 17 00:00:00 2001
From: Lain-dono <lain.dono@gmail.com>
Date: Mon, 15 Mar 2021 02:39:36 +0300
Subject: [PATCH] [spv-out] implement derivatives

---
 src/back/spv/instructions.rs | 24 ++++++++++++++++++++++++
 src/back/spv/writer.rs       | 12 ++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/src/back/spv/instructions.rs b/src/back/spv/instructions.rs
index f8366b96c5..b1033c8023 100644
--- a/src/back/spv/instructions.rs
+++ b/src/back/spv/instructions.rs
@@ -683,6 +683,30 @@ impl super::Instruction {
     // Derivative Instructions
     //
 
+    pub(super) fn derive_x(result_type_id: Word, id: Word, expr_id: Word) -> Self {
+        let mut instruction = Self::new(Op::DPdx);
+        instruction.set_type(result_type_id);
+        instruction.set_result(id);
+        instruction.add_operand(expr_id);
+        instruction
+    }
+
+    pub(super) fn derive_y(result_type_id: Word, id: Word, expr_id: Word) -> Self {
+        let mut instruction = Self::new(Op::DPdy);
+        instruction.set_type(result_type_id);
+        instruction.set_result(id);
+        instruction.add_operand(expr_id);
+        instruction
+    }
+
+    pub(super) fn derive_width(result_type_id: Word, id: Word, expr_id: Word) -> Self {
+        let mut instruction = Self::new(Op::Fwidth);
+        instruction.set_type(result_type_id);
+        instruction.set_result(id);
+        instruction.add_operand(expr_id);
+        instruction
+    }
+
     //
     // Control-Flow Instructions
     //
diff --git a/src/back/spv/writer.rs b/src/back/spv/writer.rs
index 59fe3b5cdb..db143edabb 100644
--- a/src/back/spv/writer.rs
+++ b/src/back/spv/writer.rs
@@ -1901,6 +1901,18 @@ impl Writer {
                 block.body.push(instruction);
                 id
             }
+            crate::Expression::Derivative { axis, expr } => {
+                use crate::DerivativeAxis;
+
+                let id = self.generate_id();
+                let expr_id = self.cached[expr];
+                block.body.push(match axis {
+                    DerivativeAxis::X => Instruction::derive_x(result_type_id, id, expr_id),
+                    DerivativeAxis::Y => Instruction::derive_y(result_type_id, id, expr_id),
+                    DerivativeAxis::Width => Instruction::derive_width(result_type_id, id, expr_id),
+                });
+                id
+            }
             ref other => {
                 log::error!("unimplemented {:?}", other);
                 return Err(Error::FeatureNotImplemented("expression"));