From 9ce31581934ebe2ef5fcc0acf0933c5caa1ba428 Mon Sep 17 00:00:00 2001
From: Mark Satterthwaite <mark.satterthwaite@epicgames.com>
Date: Wed, 14 Aug 2019 10:57:23 -0400
Subject: [PATCH] When compiling from HLSL which pads and aligns
 float[]/float2[] within structures to float4[] we need to unpack the original
 type in Metal from the float4.

---
 spirv_glsl.hpp |  4 +++-
 spirv_msl.cpp  | 28 +++++++++++++++++++++++++++-
 spirv_msl.hpp  |  3 +++
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/spirv_glsl.hpp b/spirv_glsl.hpp
index 315df49d..5c78afda 100644
--- a/spirv_glsl.hpp
+++ b/spirv_glsl.hpp
@@ -528,7 +528,9 @@ protected:
 	std::string to_unpacked_expression(uint32_t id, bool register_expression_read = true);
 	std::string to_unpacked_row_major_matrix_expression(uint32_t id);
 	std::string to_enclosed_unpacked_expression(uint32_t id, bool register_expression_read = true);
-	std::string to_dereferenced_expression(uint32_t id, bool register_expression_read = true);
+    /* UE Change Begin: Metal expands float[]/float2[] members inside structs to float4[] so we must unpack */
+	virtual std::string to_dereferenced_expression(uint32_t id, bool register_expression_read = true);
+    /* UE Change End: Metal expands float[]/float2[] members inside structs to float4[] so we must unpack */
 	std::string to_pointer_expression(uint32_t id, bool register_expression_read = true);
 	std::string to_enclosed_pointer_expression(uint32_t id, bool register_expression_read = true);
 	std::string to_extract_component_expression(uint32_t id, uint32_t index);
diff --git a/spirv_msl.cpp b/spirv_msl.cpp
index 9ab847c2..4c955675 100644
--- a/spirv_msl.cpp
+++ b/spirv_msl.cpp
@@ -3120,6 +3120,32 @@ void CompilerMSL::emit_store_statement(uint32_t lhs_expression, uint32_t rhs_exp
 	}
 }
 
+/* UE Change Begin: Metal expands float[]/float2[] members inside structs to float4[] so we must unpack */
+string CompilerMSL::to_dereferenced_expression(uint32_t id, bool register_expression_read)
+{
+	auto &type = expression_type(id);
+	if (!type.pointer || !should_dereference(id))
+	{
+		uint32_t packed_type_id = get_extended_decoration(id, SPIRVCrossDecorationPhysicalTypePacked);
+		const SPIRType *packed_type = nullptr;
+		if (packed_type_id)
+			packed_type = &get<SPIRType>(packed_type_id);
+		
+		if (packed_type && is_array(*packed_type) && is_scalar(*packed_type))
+			return to_unpacked_expression(id, register_expression_read);
+	}
+	
+	return CompilerGLSL::to_dereferenced_expression(id, register_expression_read);
+}
+
+static bool expression_ends_with(string const& expr_str, std::string const& ending)
+{
+	if (expr_str.length() >= ending.length())
+		return (0 == expr_str.compare(expr_str.length() - ending.length(), ending.length(), ending));
+	else
+		return false;
+}
+
 // Converts the format of the current expression from packed to unpacked,
 // by wrapping the expression in a constructor of the appropriate type.
 // Also, handle special physical ID remapping scenarios, similar to emit_store_statement().
@@ -3141,7 +3167,7 @@ string CompilerMSL::unpack_expression_type(string expr_str, const SPIRType &type
 	};
 
 	// std140 array cases for vectors.
-	if (physical_type && is_vector(*physical_type) && is_array(*physical_type) && physical_type->vecsize > type.vecsize)
+	if (physical_type && is_vector(*physical_type) && is_array(*physical_type) && physical_type->vecsize > type.vecsize && !expression_ends_with(expr_str, swizzle_lut[type.vecsize - 1]))
 	{
 		assert(type.vecsize >= 1 && type.vecsize <= 3);
 		return enclose_expression(expr_str) + swizzle_lut[type.vecsize - 1];
diff --git a/spirv_msl.hpp b/spirv_msl.hpp
index d48f3d8d..7c394307 100644
--- a/spirv_msl.hpp
+++ b/spirv_msl.hpp
@@ -580,6 +580,9 @@ protected:
 	                             uint32_t grad_y, uint32_t lod, uint32_t coffset, uint32_t offset, uint32_t bias,
 	                             uint32_t comp, uint32_t sample, uint32_t minlod, bool *p_forward) override;
 	std::string to_initializer_expression(const SPIRVariable &var) override;
+	/* UE Change Begin: Metal expands float[]/float2[] members inside structs to float4[] so we must unpack */
+	virtual std::string to_dereferenced_expression(uint32_t id, bool register_expression_read = true) override;
+	/* UE Change End: Metal expands float[]/float2[] members inside structs to float4[] so we must unpack */
 	std::string unpack_expression_type(std::string expr_str, const SPIRType &type, uint32_t physical_type_id,
 	                                   bool is_packed, bool row_major) override;