+ unsigned layout_hash = (info ? info->layout_hash : prog.get_uniform_layout_hash());
+
+ map<unsigned, Block>::iterator i = blocks.find(layout_hash);
+ if(i==blocks.end())
+ {
+ i = blocks.insert(BlockMap::value_type(layout_hash, Block())).first;
+ if(info)
+ {
+ find_uniforms_for_block(i->second, *info);
+
+ if(!i->second.uniforms.empty())
+ {
+ i->second.block = create_block(*info);
+ i->second.changes = VALUES_CHANGED;
+ }
+ }
+ else
+ {
+ i->second.block = new UniformBlock;
+ i->second.changes = VALUES_CHANGED;
+ }
+ }
+ else if(info && i->second.changes==KEYS_CHANGED)
+ {
+ find_uniforms_for_block(i->second, *info);
+ if(!i->second.uniforms.empty())
+ {
+ if(!i->second.block)
+ i->second.block = create_block(*info);
+ i->second.changes = VALUES_CHANGED;
+ }
+ else
+ i->second.changes = NO_CHANGES;
+ }
+
+ if(!i->second.block)
+ return 0;
+
+ UniformBlock &block = *i->second.block;
+ if(i->second.changes)
+ {
+ if(info)
+ {
+ vector<const Program::UniformInfo *>::const_iterator j = info->uniforms.begin();
+ map<unsigned, const Uniform *const *>::const_iterator k = i->second.uniforms.begin();
+ while(j!=info->uniforms.end() && k!=i->second.uniforms.end())
+ {
+ if(k->first==(*j)->location)
+ {
+ block.attach(**j, **k->second);
+ ++k;
+ }
+ ++j;
+ }
+ }
+ else
+ {
+ for(UniformMap::const_iterator j=uniforms.begin(); j!=uniforms.end(); ++j)
+ {
+ int loc = prog.get_uniform_location(j->first);
+ if(loc>=0)
+ block.attach(loc, *j->second);
+ }
+ }
+ i->second.changes = NO_CHANGES;
+ }
+
+ return █