HLSL: Support depth comparison texture sampling in SM 2/3.

spirv_hlsl.cpp

@@ -373,8 +373,6 @@ string CompilerHLSL::image_type_hlsl_legacy(const SPIRType &type, uint32_t id)
 		res += "MS";
 	if (type.image.arrayed)
 		res += "Array";
-	if (image_is_comparison(type, id))
-		res += "Shadow";
 
 	return res;
 }
@@ -2926,14 +2924,15 @@ void CompilerHLSL::emit_texture_op(const Instruction &i, bool sparse)
 				SPIRV_CROSS_THROW("textureGather is not supported in HLSL shader model 2/3.");
 			if (offset || coffset)
 				SPIRV_CROSS_THROW("textureOffset is not supported in HLSL shader model 2/3.");
-			if (proj)
-				texop += "proj";
+
 			if (grad_x || grad_y)
 				texop += "grad";
-			if (lod)
+			else if (lod)
 				texop += "lod";
-			if (bias)
+			else if (bias)
 				texop += "bias";
+			else if (proj || dref)
+				texop += "proj";
 		}
 	}
 
@@ -2987,35 +2986,42 @@ void CompilerHLSL::emit_texture_op(const Instruction &i, bool sparse)
 
 	if (hlsl_options.shader_model < 40)
 	{
-		string coord_filler;
-		uint32_t modifier_count = 0;
-
-		if (lod)
+		if (dref)
 		{
+			if (imgtype.image.dim != spv::Dim1D || imgtype.image.dim != spv::Dim2D)
+				SPIRV_CROSS_THROW("Depth comparison is only supported for 1D and 2D textures in HLSL shader model 2/3.");
+
+			forward = forward && should_forward(dref);
 			for (uint32_t size = coord_components; size < 3; ++size)
-				coord_filler += ", 0.0";
-			coord_expr = "float4(" + coord_expr + coord_filler + ", " + to_expression(lod) + ")";
-			modifier_count++;
+				coord_expr += ", " + to_expression(dref);
 		}
-
-		if (bias)
+		else if (lod || bias || proj)
 		{
 			for (uint32_t size = coord_components; size < 3; ++size)
-				coord_filler += ", 0.0";
-			coord_expr = "float4(" + coord_expr + coord_filler + ", " + to_expression(bias) + ")";
-			modifier_count++;
+				coord_expr += ", 0.0";
 		}
 
-		if (proj)
+		if (lod)
 		{
-			for (uint32_t size = coord_components; size < 3; ++size)
-				coord_filler += ", 0.0";
-			coord_expr = "float4(" + coord_expr + coord_filler + ", " +
+			coord_expr = "float4(" + coord_expr + ", " + to_expression(lod) + ")";
+		}
+		else if (bias)
+		{
+			coord_expr = "float4(" + coord_expr + ", " + to_expression(bias) + ")";
+		}
+		else if (proj)
+		{
+			coord_expr = "float4(" + coord_expr + ", " +
 			             to_extract_component_expression(coord, coord_components) + ")";
-			modifier_count++;
+		}
+		else if (dref)
+		{
+			// A "normal" sample gets fed into tex2Dproj as well, because the
+			// regular tex2D accepts only two coordinates.
+			coord_expr = "float4(" + coord_expr + ", 1.0)";
 		}
 
-		if (modifier_count > 1)
+		if (!!lod + !!bias + !!proj > 1)
 			SPIRV_CROSS_THROW("Legacy HLSL can only use one of lod/bias/proj modifiers.");
 	}
 
@@ -3029,11 +3035,8 @@ void CompilerHLSL::emit_texture_op(const Instruction &i, bool sparse)
 		expr += ", ";
 	expr += coord_expr;
 
-	if (dref)
+	if (dref && hlsl_options.shader_model >= 40)
 	{
-		if (hlsl_options.shader_model < 40)
-			SPIRV_CROSS_THROW("Legacy HLSL does not support comparison sampling.");
-
 		forward = forward && should_forward(dref);
 		expr += ", ";