Avoid needless second pass on non-glow particles.

indra/newview/lldrawpoolalpha.cpp

@@ -598,6 +598,7 @@ void LLDrawPoolAlpha::renderAlpha(U32 mask, S32 pass)
 				// If this alpha mesh has glow, then draw it a second time to add the destination-alpha (=glow).  Interleaving these state-changing calls could be expensive, but glow must be drawn Z-sorted with alpha.
 				if (current_shader && 
 					draw_glow_for_this_partition &&
+					params.mHasGlow &&	//only do this second pass for batches that actually have glow
 					params.mVertexBuffer->hasDataType(LLVertexBuffer::TYPE_EMISSIVE))
 				{
 					// install glow-accumulating blend mode

indra/newview/llvopartgroup.cpp

@@ -716,7 +716,8 @@ void LLVOPartGroup::getGeometry(S32 idx,
 	*colorsp++ = color;
 	*colorsp++ = color;
 
-	//if (pglow.mV[3] || part.mGlow.mV[3])
+	//Only add emissive attributes if glowing (doing it for all particles is INCREDIBLY inefficient as it leads to a second, slower, render pass.)
+	if (pglow.mV[3] > F_ALMOST_ZERO || part.mGlow.mV[3] > F_ALMOST_ZERO)
 	{ //only write glow if it is not zero
 		*emissivep++ = pglow;
 		*emissivep++ = pglow;