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DirectX 10
Windows Vista ships with DirectX 10 and is the only version of Windows which it is offered for, and it has a large number of changes: DirectInput will be deprecated in favor of XInput, from the Xbox team. Likewise, DirectSound will also be deprecated in favor of XACT. DirectX 10 has also dropped support for hardware accelerated audio, opting instead to render sound in software on the CPU. DirectPlay is deprecated in favor of Xbox Live whereas DirectShow will be deprecated in favor of Media Foundation, a different set of APIs debuting with Windows Vista to handle audio and video playback. DirectMusic will probably remain the only component intact.
Direct3D
A major new feature of DirectX 10 is Direct3D 10 (originally called Windows Graphics Foundation). By using the new Windows Display Driver Model, Shader Model 4 and new, more strict requirements for GPU manufacturers to claim Direct3D 10 compatibility, version 10 of Direct3D represents a departure from the practices of previous versions. In order to achieve backwards compatibility with previous versions of Direct3D, DirectX 10 actually contains three versions of Direct3D:
Direct3D 9: this API emulates all Direct3D 9 on Windows XP behavior (and it's quirks) in order to achieve full compatibility with older applications. All the details and advantages of Vista's Windows Display Driver Model are hidden from the application if WDDM drivers are installed. This is the only API available if there are only XP graphic drivers (XPDM) installed, after an upgrade to Vista for example.
Direct3D 9Ex (previously known as 9.0L): allows full access to the new capabilities of WDDM while maintaining compatibility for existing Direct3D applications by putting it in a seperate API. The transparency ("Glass") effects in Windows Aero rely on the D3D 9Ex code path. When 9Ex was still codenamed 9.0L, there were rumors that this would be Direct3D 10 for Windows XP. It was quickly pointed out that this was not the case, mainly due to lack of support for WDDM in Windows XP.
Direct3D 10
Currently, the only graphics hardware compatible with Direct3D 10 is the NVIDIA GeForce 8 Series which has thus far limited the advent of Direct3D 10-capable applications. Contrary to rumors surrounding the issue, Direct3D 10 will not be released on the Xbox 360 via a firmware update due to incompatibilities with its graphics hardware.
Prema tome, nije baš da je DX10 vs DX9 isto što i DX9 vs DX8.
Dalje, ne pričam o problemima vezanim za brzinu, normalno je da pri ovakvoj "emulaciji" dolazi do usporenja, nego pričam o sledećem problemu: primera radi, upalim spomenuti Quake 2 u soft modu, računajući da tu ne bi smelo da bude nikakvih problema jer igra ne traži nikakvu akceleraciju već gotovu sliku šalje direktno u frejmbafer preko DirectDrawa. Ne lezi vraže, sve transparentne površine (prozori itd) u igri trepere i izgledaju kao da memorija na grafičkoj crkava, a da zabava bude veća, miš se zakuca ili samo na gore ili samo na dole, tako da nema reči od igranja pomoću istog. Ponavljam, radi se o igri koja koristi DirectDraw i DirectInput iz DirectX-a 5, što nikako ne bi smelo da pravi probleme ako se već radi o tako naprednoj emulaciji. Ne znam na čemu su testirali tokom razvoja, možda na Pinballu koji dolazi uz Windows? :)