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 d840648bbc3ec0135bbb02b4dc47350cf753f03f..469cb92daba088493168f82f55e47a4b5938dccd 100644 (file)
--- 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 ec5f459ae53b59f1db6371dedcc2928e6d75cd36..4fc2e1b00c42806768e0aca28b9166eb2284939b 100644 (file)
--- 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: