Added occlusion query handle debug code.

src/bgfx.cpp

@@ -1328,6 +1328,11 @@ namespace bgfx
 	{
 		BX_CHECK(0 == m_instBufferCount, "Instance buffer allocated, but not used. This is incorrect, and causes memory leak.");
 
+		if (BX_ENABLED(BGFX_CONFIG_DEBUG_OCCLUSION) )
+		{
+			m_occlusionQuerySet.clear();
+		}
+
 		// wait for render thread to finish
 		renderSemWait();
 		frameNoRenderWait();

src/bgfx_p.h

@@ -3605,6 +3605,17 @@ namespace bgfx
 			{
 				m_uniformSet.clear();
 			}
+
+			if (BX_ENABLED(BGFX_CONFIG_DEBUG_OCCLUSION)
+			&&  isValid(_occlusionQuery) )
+			{
+				BX_CHECK(m_occlusionQuerySet.end() == m_occlusionQuerySet.find(_occlusionQuery.idx)
+					, "OcclusionQuery %d was already used for this frame."
+					, _occlusionQuery.idx
+					);
+				m_occlusionQuerySet.insert(_occlusionQuery.idx);
+			}
+
 			return m_submit->submit(_id, _program, _occlusionQuery, _depth);
 		}
 
@@ -3873,10 +3884,12 @@ namespace bgfx
 			bool m_window;
 		};
 
+		typedef stl::unordered_set<uint16_t> HandleSet;
+		HandleSet m_uniformSet;
+		HandleSet m_occlusionQuerySet;
+
 		typedef stl::unordered_map<stl::string, UniformHandle> UniformHashMap;
 		UniformHashMap m_uniformHashMap;
-		typedef stl::unordered_set<uint16_t> UniformSet;
-		UniformSet m_uniformSet;
 		UniformRef m_uniformRef[BGFX_CONFIG_MAX_UNIFORMS];
 
 		ShaderRef m_shaderRef[BGFX_CONFIG_MAX_SHADERS];

src/config.h

@@ -164,11 +164,16 @@
 #	define BGFX_CONFIG_DEBUG_MTL BGFX_CONFIG_DEBUG
 #endif // BGFX_CONFIG_DEBUG_MTL
 
-///
+/// Enable uniform debug checks.
 #ifndef BGFX_CONFIG_DEBUG_UNIFORM
 #	define BGFX_CONFIG_DEBUG_UNIFORM BGFX_CONFIG_DEBUG
 #endif // BGFX_CONFIG_DEBUG_UNIFORM
 
+/// Enable occlusion debug checks.
+#ifndef BGFX_CONFIG_DEBUG_OCCLUSION
+#	define BGFX_CONFIG_DEBUG_OCCLUSION BGFX_CONFIG_DEBUG
+#endif // BGFX_CONFIG_DEBUG_OCCLUSION
+
 #ifndef BGFX_CONFIG_MULTITHREADED
 #	define BGFX_CONFIG_MULTITHREADED ( (!BGFX_CONFIG_RENDERER_NULL)&&(0 \
 						|| BX_PLATFORM_ANDROID \