From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 1 Oct 2022 20:05:45 +0000 (+0300)
Subject: Hack to work around an issue with the flat interpolation qualifier
X-Git-Url: http://git.tdb.fi/?a=commitdiff_plain;h=0fdc229b8b43f1897de4611672ac65b4db954be0;p=libs%2Fgl.git

Hack to work around an issue with the flat interpolation qualifier

It appears that at least on my current system (GeForce 980 Ti, driver
460.91.03) vertex attributes somehow block the flat qualifier from
working on the same location.  It feels like a driver bug but that
remains to be confirmed.
---

diff --git a/source/glsl/finalize.cpp b/source/glsl/finalize.cpp
index d840648b..469cb92d 100644
--- a/source/glsl/finalize.cpp
+++ b/source/glsl/finalize.cpp
@@ -91,6 +91,8 @@ void LocationAllocator::apply(Stage &stage)
 	stage.content.visit(*this);
 
 	allocate_locations("in");
+	if(stage.type==Stage::VERTEX)
+		swap(used_locations["in"], used_vertex_attribs);
 	allocate_locations("out");
 }
 
@@ -121,6 +123,8 @@ void LocationAllocator::allocate_locations(const string &iface)
 		if(!alloc_new)
 			continue;
 
+		bool flat = ((*i)->interpolation=="flat" || ((*i)->linked_declaration && (*i)->linked_declaration->interpolation=="flat"));
+
 		set<unsigned> &used = used_locations[(*i)->interface];
 
 		unsigned size = LocationCounter().apply(**i);
@@ -128,7 +132,7 @@ void LocationAllocator::allocate_locations(const string &iface)
 		{
 			int blocking = -1;
 			for(unsigned j=0; j<size; ++j)
-				if(used.count(next+j))
+				if(used.count(next+j) || (flat && used_vertex_attribs.count(next+j)))
 					blocking = next+j;
 			if(blocking<0)
 				break;
diff --git a/source/glsl/finalize.h b/source/glsl/finalize.h
index ec5f459a..4fc2e1b0 100644
--- a/source/glsl/finalize.h
+++ b/source/glsl/finalize.h
@@ -43,6 +43,10 @@ private:
 	std::vector<VariableDeclaration *> unbound_textures;
 	std::vector<VariableDeclaration *> unbound_blocks;
 
+	/* Dirty hack to work around an issue where vertex attributes prevent the
+	flat qualifier from working on the same location. */
+	std::set<unsigned> used_vertex_attribs;
+
 public:
 	void apply(Module &, const Features &, bool = true);
 private: