Even though it generally requires a team of experienced engineers, it's often cheaper to build an engine than to license one. However, several factors make licensing diserable, even it can cost more. Because they have been used in one r more shipping products, licensed engines are often more stable. You're buying not only the engine's technology, but the time and testing that went into it. These engines also have a lower opportunity cost. If you have a team of experienced engineers, you can have them build your game instead of the engine, or build solutions or techniocal constraints of the engine. There are also marketing and hiring advantages to livensed engines. People who have purchased products using your engine have positive expectations about your game, and you even be able to hire team mebers who are already familiar with the technology. Not to be overlooked is the ability to prototype game concepts immediately because you're working with a fully finished piece of technology.
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Medal of Honor Performance Tweaking Guide