سؤال حول التحويل بين dx و gl

السلام عليكم

1-In directX, not all the rendering is done in software, just the transform and lightinging operations can be done in software or hardware. All other operations are done in hardware only.

For OpenGL, the VGA driver decides whether to use software or hardware TnL, based on the specifications of the video card. If the video card and the driver support hardware TnL, then hardware TnL will be used automatically.If not, then software TnL will be used automatically.

2-You are right, games that can support both OpenGL and directX engines write code for both OpenGL and directX.

In My opinion, this is not a good Idea, because both open GL and DirectX have different architecture and performance characteristics.

For example, For directX it is preferred to draw many triangles with one DrawPrimitive() call, to decrease the calls to DrawPrimitive() as much as possible to decrease the number of CPU cycles consumed.In OpenGL the opposite is true, where it is prefered to draw one triangle each function call.

Many other performance and architecuture difference between OpenGL and directX exist, which makes it difficult to write a game engine that has a high perfromance both on directX and OpenGL. you have to focus on one only. Most high performance game engines such as DOOM, FEAR, Half Life focuses only on one of them.

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