Sketch out interface for combined image samplers.

main.cpp

@@ -554,6 +554,8 @@ int main(int argc, char *argv[])
 
 	unique_ptr<CompilerGLSL> compiler;
 
+	bool combined_image_samplers = false;
+
 	if (args.cpp)
 	{
 		compiler = unique_ptr<CompilerGLSL>(new CompilerCPP(read_spirv_file(args.input)));
@@ -563,7 +565,10 @@ int main(int argc, char *argv[])
 	else if (args.metal)
 		compiler = unique_ptr<CompilerMSL>(new CompilerMSL(read_spirv_file(args.input)));
 	else
+	{
+		combined_image_samplers = !args.vulkan_semantics;
 		compiler = unique_ptr<CompilerGLSL>(new CompilerGLSL(read_spirv_file(args.input)));
+	}
 
 	if (!args.entry.empty())
 		compiler->set_entry_point(args.entry);
@@ -622,6 +627,17 @@ int main(int argc, char *argv[])
 		print_push_constant_resources(*compiler, res.push_constant_buffers);
 	}
 
+	if (combined_image_samplers)
+	{
+		compiler->build_combined_image_samplers();
+		// Give the remapped combined samplers new names.
+		for (auto &remap : compiler->get_combined_image_samplers())
+		{
+			compiler->set_name(remap.combined_id, join("_Combined_", compiler->get_name(remap.image_id), "_",
+			                                           compiler->get_name(remap.sampler_id)));
+		}
+	}
+
 	string glsl;
 	for (uint32_t i = 0; i < args.iterations; i++)
 		glsl = compiler->compile();

spirv_cross.cpp

@@ -2290,3 +2290,7 @@ bool Compiler::interface_variable_exists_in_entry_point(uint32_t id) const
 	return find(begin(execution.interface_variables), end(execution.interface_variables), id) !=
 	       end(execution.interface_variables);
 }
+
+void Compiler::build_combined_image_samplers()
+{
+}

spirv_cross.hpp

@@ -80,6 +80,16 @@ struct ShaderResources
 	std::vector<Resource> separate_samplers;
 };
 
+struct CombinedImageSampler
+{
+	// The ID of the sampler2D variable.
+	uint32_t combined_id;
+	// The ID of the texture2D variable.
+	uint32_t image_id;
+	// The ID of the sampler variable.
+	uint32_t sampler_id;
+};
+
 struct BufferRange
 {
 	unsigned index;
@@ -239,6 +249,28 @@ public:
 	uint32_t get_execution_mode_argument(spv::ExecutionMode mode, uint32_t index = 0) const;
 	spv::ExecutionModel get_execution_model() const;
 
+	// Analyzes all separate image and samplers used from the currently selected entry point,
+	// and re-routes them all to a combined image sampler instead.
+	// This is required to "support" separate image samplers in targets which do not natively support
+	// this feature, like GLSL/ESSL.
+	//
+	// This must be called before compile() if such remapping is desired.
+	// This call will add new sampled images to the SPIR-V,
+	// so it will appear in reflection if get_shader_resources() is called after build_combined_image_samplers.
+	//
+	// If any image/sampler remapping was found, no separate image/samplers will appear in the decompiled output,
+	// but will still appear in reflection.
+	//
+	// The resulting samplers will be void of any decorations like name, descriptor sets and binding points,
+	// so this can be added before compile() if desired.
+	void build_combined_image_samplers();
+
+	// Gets a remapping for the combined image samplers.
+	const std::vector<CombinedImageSampler> &get_combined_image_samplers() const
+	{
+		return combined_image_samplers;
+	}
+
 protected:
 	const uint32_t *stream(const Instruction &instr) const
 	{
@@ -395,6 +427,8 @@ protected:
 	// variable is part of that entry points interface.
 	bool interface_variable_exists_in_entry_point(uint32_t id) const;
 
+	std::vector<CombinedImageSampler> combined_image_samplers;
+
 private:
 	void parse();
 	void parse(const Instruction &i);

spirv_glsl.cpp

@@ -1013,6 +1013,12 @@ void CompilerGLSL::emit_uniform(const SPIRVariable &var)
 			throw CompilerError("At least ESSL 3.10 required for shader image load store.");
 	}
 
+	// If we're remapping, only emit combined samplers.
+	bool separate_image = type.basetype == SPIRType::Image && type.image.sampled == 1;
+	bool separate_sampler = type.basetype == SPIRType::Sampler;
+	if (!combined_image_samplers.empty() && separate_image && separate_sampler)
+		return;
+
 	add_resource_name(var.self);
 	statement(layout_for_variable(var), "uniform ", variable_decl(var), ";");
 }