Metro 2033 vs. STALKER - Has 4A Games stolen the X-Ray-Engine?

4A Games, developer of Metro 2033, admits they have built the 4A engine from ground up. But it looks like the X-Ray-Engine from STALKER and Sergey Grigorovich from GSC Gameworld states that he believes 4A Games have stolen their engine. Check the link for comparison shots.

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