Graphics: Fix some comments

Former-commit-id: df6d080b1ce251b7fe5707ddbb4e31773ba9035d

src/Nazara/Graphics/ForwardRenderTechnique.cpp

@@ -27,10 +27,12 @@ namespace
 		NzColor color;
 		NzVector3f position;
 		NzVector2f size;
-		NzVector2f sinCos; // doit suivre size
+		NzVector2f sinCos; // must follow `size` (both will be sent as a Vector4f)
 		NzVector2f uv;
 	};
 
+	static_assert(NzOffsetOf(BillboardPoint, sinCos) - NzOffsetOf(BillboardPoint, size) == sizeof(NzVector2f), "size and sinCos members should be packed");
+
 	unsigned int s_maxQuads = std::numeric_limits<nzUInt16>::max()/6;
 	unsigned int s_vertexBufferSize = 4*1024*1024; // 4 MiB
 }