From 561dc036f25cfd9d9bad8996b11ccd185b4bef3f Mon Sep 17 00:00:00 2001
From: Bill Hollings <bill.hollings@brenwill.com>
Date: Tue, 25 Apr 2017 16:32:16 -0400
Subject: [PATCH] CompilerMSL round floating point tex coords for read() and
 tex array index.

---
 spirv_msl.cpp | 38 ++++++++++++++++++++++----------------
 spirv_msl.hpp |  1 +
 2 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/spirv_msl.cpp b/spirv_msl.cpp
index 74ef7abb..c0324103 100644
--- a/spirv_msl.cpp
+++ b/spirv_msl.cpp
@@ -1038,9 +1038,10 @@ string CompilerMSL::to_function_args(uint32_t img, const SPIRType &imgtype, bool
 	bool forward = should_forward(coord);
 	auto coord_expr = to_enclosed_expression(coord);
 	auto &coord_type = expression_type(coord);
+	bool coord_is_fp = (coord_type.basetype == SPIRType::Float) || (coord_type.basetype == SPIRType::Double);
+	bool is_cube_fetch = false;
 
 	string tex_coords = coord_expr;
-	string face_expr;
 	const char *alt_coord = "";
 
 	switch (imgtype.image.dim)
@@ -1048,25 +1049,23 @@ string CompilerMSL::to_function_args(uint32_t img, const SPIRType &imgtype, bool
 
 	case Dim1D:
 		if (coord_type.vecsize > 1)
-		{
 			tex_coords += ".x";
-			alt_coord = ".y";
-		}
 
 		if (is_fetch)
-			tex_coords = "uint(" + tex_coords + ")";
+			tex_coords = "uint(" + round_fp_tex_coords(tex_coords, coord_is_fp) + ")";
+
+		alt_coord = ".y";
 
 		break;
 
 	case DimBuffer:
 		if (coord_type.vecsize > 1)
-		{
 			tex_coords += ".x";
-			alt_coord = ".y";
-		}
 
 		if (is_fetch)
-			tex_coords = "uint2(" + tex_coords + ", 0)"; // Metal textures are 2D
+			tex_coords = "uint2(" + round_fp_tex_coords(tex_coords, coord_is_fp) + ", 0)"; // Metal textures are 2D
+
+		alt_coord = ".y";
 
 		break;
 
@@ -1075,7 +1074,7 @@ string CompilerMSL::to_function_args(uint32_t img, const SPIRType &imgtype, bool
 			tex_coords += ".xy";
 
 		if (is_fetch)
-			tex_coords = "uint2(" + tex_coords + ")";
+			tex_coords = "uint2(" + round_fp_tex_coords(tex_coords, coord_is_fp) + ")";
 
 		alt_coord = ".z";
 
@@ -1086,7 +1085,7 @@ string CompilerMSL::to_function_args(uint32_t img, const SPIRType &imgtype, bool
 			tex_coords += ".xyz";
 
 		if (is_fetch)
-			tex_coords = "uint3(" + tex_coords + ")";
+			tex_coords = "uint3(" + round_fp_tex_coords(tex_coords, coord_is_fp) + ")";
 
 		alt_coord = ".w";
 
@@ -1095,8 +1094,9 @@ string CompilerMSL::to_function_args(uint32_t img, const SPIRType &imgtype, bool
 	case DimCube:
 		if (is_fetch)
 		{
-			tex_coords = "uint2(" + tex_coords + ".xy)";
-			face_expr = coord_expr + ".z";
+			is_cube_fetch = true;
+			tex_coords += ".xy";
+			tex_coords = "uint2(" + round_fp_tex_coords(tex_coords, coord_is_fp) + ")";
 		}
 		else
 		{
@@ -1121,12 +1121,12 @@ string CompilerMSL::to_function_args(uint32_t img, const SPIRType &imgtype, bool
 	farg_str += tex_coords;
 
 	// If fetch from cube, add face explicitly
-	if (!face_expr.empty())
-		farg_str += ", uint(" + face_expr + ")";
+	if (is_cube_fetch)
+		farg_str += ", uint(" + round_fp_tex_coords(coord_expr + ".z", coord_is_fp) + ")";
 
 	// If array, use alt coord
 	if (imgtype.image.arrayed)
-		farg_str += ", uint(" + coord_expr + alt_coord + ")";
+		farg_str += ", uint(" + round_fp_tex_coords(coord_expr + alt_coord, coord_is_fp) + ")";
 
 	// Depth compare reference value
 	if (dref)
@@ -1232,6 +1232,12 @@ string CompilerMSL::to_function_args(uint32_t img, const SPIRType &imgtype, bool
 	return farg_str;
 }
 
+// If the texture coordinates are floating point, invokes MSL round() function to round them.
+string CompilerMSL::round_fp_tex_coords(string tex_coords, bool coord_is_fp)
+{
+	return coord_is_fp ? ("round(" + tex_coords + ")") : tex_coords;
+}
+
 // Returns a string to use in an image sampling function argument.
 // The ID must be a scalar constant.
 string CompilerMSL::to_component_argument(uint32_t id)
diff --git a/spirv_msl.hpp b/spirv_msl.hpp
index ecad29e6..a46ca0d9 100644
--- a/spirv_msl.hpp
+++ b/spirv_msl.hpp
@@ -181,6 +181,7 @@ protected:
 	std::string built_in_func_arg(spv::BuiltIn builtin, bool prefix_comma);
 	std::string member_attribute_qualifier(const SPIRType &type, uint32_t index);
 	std::string argument_decl(const SPIRFunction::Parameter &arg);
+	std::string round_fp_tex_coords(std::string tex_coords, bool coord_is_fp);
 	uint32_t get_metal_resource_index(SPIRVariable &var, SPIRType::BaseType basetype);
 	uint32_t get_ordered_member_location(uint32_t type_id, uint32_t index);
 	size_t get_declared_type_size(uint32_t type_id) const;