From 6997ed1c07c382c0f66c57c080934ad53e1d3713 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 8 Nov 2021 18:17:51 +0200
Subject: [PATCH] Allow a push constant block to be specified, but flatten it
 for now

It's needed for Vulkan, but OpenGL does not have push constants.
---
 source/glsl/finalize.cpp | 29 ++++++++++++++++++++++-------
 source/glsl/validate.cpp | 13 +++++++++++++
 2 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/source/glsl/finalize.cpp b/source/glsl/finalize.cpp
index f005d87d..2fff7549 100644
--- a/source/glsl/finalize.cpp
+++ b/source/glsl/finalize.cpp
@@ -221,15 +221,25 @@ void LocationAllocator::visit(InterfaceBlock &iface)
 
 	if(iface.interface=="uniform")
 	{
-		int bind_point = (iface.layout ? get_layout_value(*iface.layout, "binding") : -1);
+		bool push_constant = false;
+		if(iface.layout)
+		{
+			auto i = find_member(iface.layout->qualifiers, string("push_constant"), &Layout::Qualifier::name);
+			push_constant = (i!=iface.layout->qualifiers.end());
+		}
 
-		if(bind_point>=0)
+		if(!push_constant)
 		{
-			used_bindings[0].insert(bind_point);
-			uniforms[iface.block_name].bind_point = bind_point;
+			int bind_point = (iface.layout ? get_layout_value(*iface.layout, "binding") : -1);
+
+			if(bind_point>=0)
+			{
+				used_bindings[0].insert(bind_point);
+				uniforms[iface.block_name].bind_point = bind_point;
+			}
+			else
+				unbound_blocks.push_back(&iface);
 		}
-		else
-			unbound_blocks.push_back(&iface);
 	}
 }
 
@@ -636,6 +646,7 @@ bool LegacyConverter::supports_interface_block_location() const
 
 void LegacyConverter::visit(InterfaceBlock &iface)
 {
+	bool push_constant = false;
 	if(iface.layout)
 	{
 		for(auto i=iface.layout->qualifiers.begin(); i!=iface.layout->qualifiers.end(); )
@@ -648,14 +659,18 @@ void LegacyConverter::visit(InterfaceBlock &iface)
 				i = iface.layout->qualifiers.erase(i);
 			}
 			else
+			{
+				if(i->name=="push_constant")
+					push_constant = true;
 				++i;
+			}
 		}
 
 		if(iface.layout->qualifiers.empty())
 			iface.layout = 0;
 	}
 
-	if(!supports_interface_blocks(iface.interface) && iface.type_declaration)
+	if((!supports_interface_blocks(iface.interface) || push_constant) && iface.type_declaration)
 	{
 		if(!iface.instance_name.empty())
 			unsupported("ARB_uniform_buffer_object required for interface block instances");
diff --git a/source/glsl/validate.cpp b/source/glsl/validate.cpp
index f12177db..2da8345d 100644
--- a/source/glsl/validate.cpp
+++ b/source/glsl/validate.cpp
@@ -49,6 +49,8 @@ const char *DeclarationValidator::describe_variable(ScopeType scope)
 
 void DeclarationValidator::visit(Layout &layout)
 {
+	bool push_constant = false;
+	bool binding = false;
 	for(const Layout::Qualifier &q: layout.qualifiers)
 	{
 		bool allowed = false;
@@ -58,6 +60,8 @@ void DeclarationValidator::visit(Layout &layout)
 			allowed = (variable && scope==GLOBAL);
 		else if(q.name=="binding" || q.name=="set")
 		{
+			binding = true;
+
 			if(q.name=="set")
 			{
 				error(layout, "Layout qualifier 'set' not allowed when targeting OpenGL");
@@ -141,6 +145,12 @@ void DeclarationValidator::visit(Layout &layout)
 				err_descr = "non-matrix variable";
 			}
 		}
+		else if(q.name=="push_constant")
+		{
+			push_constant = true;
+			allowed = (iface_block && !variable && iface_block->interface=="uniform");
+			value = false;
+		}
 
 		if(!allowed)
 		{
@@ -162,6 +172,9 @@ void DeclarationValidator::visit(Layout &layout)
 		else if(!value && q.has_value)
 			error(layout, format("Layout qualifier '%s' does not allow a value", q.name));
 	}
+
+	if(push_constant && binding)
+		error(layout, "Layout qualifier 'push_constant' not allowed together with 'binding' or 'set'");
 }
 
 void DeclarationValidator::visit(InterfaceLayout &layout)
-- 
2.43.0