From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 26 Sep 2014 10:06:52 +0000 (+0300)
Subject: Deal with hash collisions in assigning uniform block bind points
X-Git-Url: http://git.tdb.fi/?p=libs%2Fgl.git;a=commitdiff_plain;h=69eff0e5febbb008f812d8e83e2332d11c42fbfd

Deal with hash collisions in assigning uniform block bind points
---

diff --git a/source/program.cpp b/source/program.cpp
index 66ca36b1..e16776f8 100644
--- a/source/program.cpp
+++ b/source/program.cpp
@@ -1,5 +1,6 @@
 #include <algorithm>
 #include <cstring>
+#include <set>
 #include <msp/core/hash.h>
 #include <msp/core/maputils.h>
 #include <msp/gl/extensions/arb_shader_objects.h>
@@ -156,6 +157,7 @@ void Program::link()
 
 	if(ARB_uniform_buffer_object)
 	{
+		std::set<unsigned> used_bind_points;
 		count = get_program_i(id, GL_ACTIVE_UNIFORM_BLOCKS);
 		for(unsigned i=0; i<count; ++i)
 		{
@@ -215,8 +217,12 @@ void Program::link()
 
 			sort(info.uniforms.begin(), info.uniforms.end(), uniform_location_compare);
 			info.layout_hash = compute_layout_hash(info.uniforms);
-			info.bind_point = info.layout_hash%BufferRange::get_n_uniform_buffer_bindings();
+			unsigned n_bindings = BufferRange::get_n_uniform_buffer_bindings();
+			info.bind_point = info.layout_hash%n_bindings;
+			while(used_bind_points.count(info.bind_point))
+				info.bind_point = (info.bind_point+1)%n_bindings;
 			glUniformBlockBinding(id, i, info.bind_point);
+			used_bind_points.insert(info.bind_point);
 		}
 	}