GLSL: Support emitting push constant block as a plain UBO.

CMakeLists.txt

@@ -195,7 +195,7 @@ endif()
 
 if (SPIRV_CROSS_SHARED)
 	set(spirv-cross-abi-major 0)
-	set(spirv-cross-abi-minor 2)
+	set(spirv-cross-abi-minor 3)
 	set(spirv-cross-abi-patch 0)
 	set(SPIRV_CROSS_VERSION ${spirv-cross-abi-major}.${spirv-cross-abi-minor}.${spirv-cross-abi-patch})
 	set(SPIRV_CROSS_INSTALL_LIB_DIR ${CMAKE_INSTALL_PREFIX}/lib)

main.cpp

@@ -496,6 +496,7 @@ struct CLIArguments
 	bool msl_pad_fragment_output = false;
 	bool msl_domain_lower_left = false;
 	bool msl_argument_buffers = false;
+	bool glsl_emit_push_constant_as_ubo = false;
 	vector<uint32_t> msl_discrete_descriptor_sets;
 	vector<PLSArg> pls_in;
 	vector<PLSArg> pls_out;
@@ -547,6 +548,7 @@ static void print_help()
 	                "\t[--iterations iter]\n"
 	                "\t[--cpp]\n"
 	                "\t[--cpp-interface-name <name>]\n"
+	                "\t[--glsl-emit-push-constant-as-ubo]\n"
 	                "\t[--msl]\n"
 	                "\t[--msl-version <MMmmpp>]\n"
 	                "\t[--msl-capture-output]\n"
@@ -714,6 +716,7 @@ static int main_inner(int argc, char *argv[])
 	cbs.add("--reflect", [&args](CLIParser &parser) { args.reflect = parser.next_value_string("json"); });
 	cbs.add("--cpp-interface-name", [&args](CLIParser &parser) { args.cpp_interface_name = parser.next_string(); });
 	cbs.add("--metal", [&args](CLIParser &) { args.msl = true; }); // Legacy compatibility
+	cbs.add("--glsl-emit-push-constant-as-ubo", [&args](CLIParser &) { args.glsl_emit_push_constant_as_ubo = true; });
 	cbs.add("--msl", [&args](CLIParser &) { args.msl = true; });
 	cbs.add("--hlsl", [&args](CLIParser &) { args.hlsl = true; });
 	cbs.add("--hlsl-enable-compat", [&args](CLIParser &) { args.hlsl_compat = true; });
@@ -986,6 +989,7 @@ static int main_inner(int argc, char *argv[])
 	opts.vertex.fixup_clipspace = args.fixup;
 	opts.vertex.flip_vert_y = args.yflip;
 	opts.vertex.support_nonzero_base_instance = args.support_nonzero_baseinstance;
+	opts.emit_push_constant_as_uniform_buffer = args.glsl_emit_push_constant_as_ubo;
 	compiler->set_common_options(opts);
 
 	// Set HLSL specific options.

reference/opt/shaders/vulkan/frag/push-constant-as-ubo.push-ubo.vk.frag

@@ -0,0 +1,14 @@
+#version 450
+
+layout(std140) uniform UBO
+{
+    float ubo[4];
+} _14;
+
+layout(location = 0) out float FragColor;
+
+void main()
+{
+    FragColor = _14.ubo[1];
+}
+

reference/opt/shaders/vulkan/frag/push-constant-as-ubo.push-ubo.vk.frag.vk

@@ -0,0 +1,14 @@
+#version 450
+
+layout(push_constant, std140) uniform UBO
+{
+    float ubo[4];
+} _14;
+
+layout(location = 0) out float FragColor;
+
+void main()
+{
+    FragColor = _14.ubo[1];
+}
+

reference/shaders/vulkan/frag/push-constant-as-ubo.push-ubo.vk.frag

@@ -0,0 +1,14 @@
+#version 450
+
+layout(std140) uniform UBO
+{
+    float ubo[4];
+} _14;
+
+layout(location = 0) out float FragColor;
+
+void main()
+{
+    FragColor = _14.ubo[1];
+}
+

reference/shaders/vulkan/frag/push-constant-as-ubo.push-ubo.vk.frag.vk

@@ -0,0 +1,14 @@
+#version 450
+
+layout(push_constant, std140) uniform UBO
+{
+    float ubo[4];
+} _14;
+
+layout(location = 0) out float FragColor;
+
+void main()
+{
+    FragColor = _14.ubo[1];
+}
+

shaders/vulkan/frag/push-constant-as-ubo.push-ubo.vk.frag

@@ -0,0 +1,13 @@
+#version 450
+
+layout(push_constant, std140) uniform UBO
+{
+   float ubo[4];
+};
+
+layout(location = 0) out float FragColor;
+
+void main()
+{
+   FragColor = ubo[1];
+}

spirv_cross_c.cpp

@@ -316,14 +316,19 @@ spvc_result spvc_compiler_create_compiler_options(spvc_compiler compiler, spvc_c
 		{
 		case SPVC_BACKEND_MSL:
 			opt->backend_flags |= SPVC_COMPILER_OPTION_MSL_BIT | SPVC_COMPILER_OPTION_COMMON_BIT;
+			opt->glsl = static_cast<CompilerMSL *>(compiler->compiler.get())->get_common_options();
+			opt->msl = static_cast<CompilerMSL *>(compiler->compiler.get())->get_msl_options();
 			break;
 
 		case SPVC_BACKEND_HLSL:
 			opt->backend_flags |= SPVC_COMPILER_OPTION_HLSL_BIT | SPVC_COMPILER_OPTION_COMMON_BIT;
+			opt->glsl = static_cast<CompilerHLSL *>(compiler->compiler.get())->get_common_options();
+			opt->hlsl = static_cast<CompilerHLSL *>(compiler->compiler.get())->get_hlsl_options();
 			break;
 
 		case SPVC_BACKEND_GLSL:
 			opt->backend_flags |= SPVC_COMPILER_OPTION_GLSL_BIT | SPVC_COMPILER_OPTION_COMMON_BIT;
+			opt->glsl = static_cast<CompilerGLSL *>(compiler->compiler.get())->get_common_options();
 			break;
 
 		default:
@@ -474,6 +479,10 @@ spvc_result spvc_compiler_options_set_uint(spvc_compiler_options options, spvc_c
 		options->msl.argument_buffers = value != 0;
 		break;
 
+	case SPVC_COMPILER_OPTION_GLSL_EMIT_PUSH_CONSTANT_AS_UNIFORM_BUFFER:
+		options->glsl.emit_push_constant_as_uniform_buffer = value != 0;
+		break;
+
 	default:
 		options->context->report_error("Unknown option.");
 		return SPVC_ERROR_INVALID_ARGUMENT;

spirv_cross_c.h

@@ -33,7 +33,7 @@ extern "C" {
 /* Bumped if ABI or API breaks backwards compatibility. */
 #define SPVC_C_API_VERSION_MAJOR 0
 /* Bumped if APIs or enumerations are added in a backwards compatible way. */
-#define SPVC_C_API_VERSION_MINOR 2
+#define SPVC_C_API_VERSION_MINOR 3
 /* Bumped if internal implementation details change. */
 #define SPVC_C_API_VERSION_PATCH 0
 
@@ -420,6 +420,8 @@ typedef enum spvc_compiler_option
 	SPVC_COMPILER_OPTION_MSL_PLATFORM = 31 | SPVC_COMPILER_OPTION_MSL_BIT,
 	SPVC_COMPILER_OPTION_MSL_ARGUMENT_BUFFERS = 32 | SPVC_COMPILER_OPTION_MSL_BIT,
 
+	SPVC_COMPILER_OPTION_GLSL_EMIT_PUSH_CONSTANT_AS_UNIFORM_BUFFER = 33 | SPVC_COMPILER_OPTION_GLSL_BIT,
+
 	SPVC_COMPILER_OPTION_INT_MAX = 0x7fffffff
 } spvc_compiler_option;
 

spirv_glsl.cpp

@@ -1365,10 +1365,12 @@ string CompilerGLSL::layout_for_variable(const SPIRVariable &var)
 	bool push_constant_block = options.vulkan_semantics && var.storage == StorageClassPushConstant;
 	bool ssbo_block = var.storage == StorageClassStorageBuffer ||
 	                  (var.storage == StorageClassUniform && typeflags.get(DecorationBufferBlock));
+	bool emulated_ubo = var.storage == StorageClassPushConstant && options.emit_push_constant_as_uniform_buffer;
+	bool ubo_block = var.storage == StorageClassUniform && typeflags.get(DecorationBlock);
 
 	// Instead of adding explicit offsets for every element here, just assume we're using std140 or std430.
 	// If SPIR-V does not comply with either layout, we cannot really work around it.
-	if (can_use_buffer_blocks && var.storage == StorageClassUniform && typeflags.get(DecorationBlock))
+	if (can_use_buffer_blocks && (ubo_block || emulated_ubo))
 	{
 		if (buffer_is_packing_standard(type, BufferPackingStd140))
 			attr.push_back("std140");
@@ -1379,7 +1381,7 @@ string CompilerGLSL::layout_for_variable(const SPIRVariable &var)
 			// however, we can only use layout(offset) on the block itself, not any substructs, so the substructs better be the appropriate layout.
 			// Enhanced layouts seem to always work in Vulkan GLSL, so no need for extensions there.
 			if (options.es && !options.vulkan_semantics)
-				SPIRV_CROSS_THROW("Push constant block cannot be expressed as neither std430 nor std140. ES-targets do "
+				SPIRV_CROSS_THROW("Uniform buffer block cannot be expressed as std140. ES-targets do "
 				                  "not support GL_ARB_enhanced_layouts.");
 			if (!options.es && !options.vulkan_semantics && options.version < 440)
 				require_extension_internal("GL_ARB_enhanced_layouts");
@@ -1461,6 +1463,8 @@ void CompilerGLSL::emit_push_constant_block(const SPIRVariable &var)
 		emit_buffer_block_flattened(var);
 	else if (options.vulkan_semantics)
 		emit_push_constant_block_vulkan(var);
+	else if (options.emit_push_constant_as_uniform_buffer)
+		emit_buffer_block_native(var);
 	else
 		emit_push_constant_block_glsl(var);
 }

spirv_glsl.hpp

@@ -96,6 +96,9 @@ public:
 		// If disabled on older targets, binding decorations will be stripped.
 		bool enable_420pack_extension = true;
 
+		// In non-Vulkan GLSL, emit push constant blocks as UBOs rather than plain uniforms.
+		bool emit_push_constant_as_uniform_buffer = false;
+
 		enum Precision
 		{
 			DontCare,

test_shaders.py

@@ -302,7 +302,7 @@ def validate_shader(shader, vulkan, paths):
     else:
         subprocess.check_call([paths.glslang, shader])
 
-def cross_compile(shader, vulkan, spirv, invalid_spirv, eliminate, is_legacy, flatten_ubo, sso, flatten_dim, opt, paths):
+def cross_compile(shader, vulkan, spirv, invalid_spirv, eliminate, is_legacy, flatten_ubo, sso, flatten_dim, opt, push_ubo, paths):
     spirv_path = create_temporary()
     glsl_path = create_temporary(os.path.basename(shader))
 
@@ -335,6 +335,8 @@ def cross_compile(shader, vulkan, spirv, invalid_spirv, eliminate, is_legacy, fl
         extra_args += ['--separate-shader-objects']
     if flatten_dim:
         extra_args += ['--flatten-multidimensional-arrays']
+    if push_ubo:
+        extra_args += ['--glsl-emit-push-constant-as-ubo']
 
     spirv_cross_path = './spirv-cross'
 
@@ -496,6 +498,9 @@ def shader_is_flatten_dimensions(shader):
 def shader_is_noopt(shader):
     return '.noopt.' in shader
 
+def shader_is_push_ubo(shader):
+    return '.push-ubo.' in shader
+
 def test_shader(stats, shader, update, keep, opt, paths):
     joined_path = os.path.join(shader[0], shader[1])
     vulkan = shader_is_vulkan(shader[1])
@@ -508,9 +513,10 @@ def test_shader(stats, shader, update, keep, opt, paths):
     sso = shader_is_sso(shader[1])
     flatten_dim = shader_is_flatten_dimensions(shader[1])
     noopt = shader_is_noopt(shader[1])
+    push_ubo = shader_is_push_ubo(shader[1])
 
     print('Testing shader:', joined_path)
-    spirv, glsl, vulkan_glsl = cross_compile(joined_path, vulkan, is_spirv, invalid_spirv, eliminate, is_legacy, flatten_ubo, sso, flatten_dim, opt and (not noopt), paths)
+    spirv, glsl, vulkan_glsl = cross_compile(joined_path, vulkan, is_spirv, invalid_spirv, eliminate, is_legacy, flatten_ubo, sso, flatten_dim, opt and (not noopt), push_ubo, paths)
 
     # Only test GLSL stats if we have a shader following GL semantics.
     if stats and (not vulkan) and (not is_spirv) and (not desktop):