The subject of DirectX 11.1 e.g. the DirectX powering the Windows 8 operating system has been a subject of quite a few controversies. First and foremost, Microsoft seemed to finally lost the plot by making announcements that 11.1 will only be available with Windows 8, then publishing 11.1 updates for Windows 7.
Nvidia GK104 die shot: the chip that powers GTX 660 OEM (& 660 Ti), 670, 680 and 690 is DirectX 11.1 compliant with a "but..."
The latest controversy comes from German website Heise.de, where it was reported that Nvidia Kepler GPUs don't feature full hardware support for DirectX 11.1. We contacted Nvidia over it, and received the following answer from Lars Weinand, Technical Marketing Manager at Nvidia EMEA:
"The GTX 680 supports DirectX 11.1 with hardware feature level 11_0, including all optional features. This includes a number of features useful for game developers such as:
- Partial constant buffer updates
- Logic operations in the Output Merger
- 16bpp rendering
- UAV-only rendering
- Partial clears
- Large constant buffers
We did not enable four non-gaming features in Hardware in Kepler (for 11_1):
- Target-Independent Rasterization (2D rendering only)
- 16xMSAA Rasterization (2D rendering only)
- Orthogonal Line Rendering Mode
- UAV in non-pixel-shader stages
So basically, we do support 11.1 features with 11_0 feature level through the DirectX 11.1 API. We do not support feature level 11_1. This is a bit confusing, due to Microsoft naming. So we do support 11.1 from a feature level for gaming related features."
Furthermore, we were directed towards MSDN library page, where the different features were listed. You can check the "Direct3D Feature Levels (Windows)" here.
Based on the Heise.de report and the answer from Nvidia, we asked our friends among AAA game developers to get clarification on how are they making that distinction. Lead engine developer for a AAA franchise that is published on PC, Xbox 360 and PlayStation 3, and is at work with next-gen engine that only works on DirectX 11-capable PC's, Xbox Next and PlayStation 4 told us the following:
"DirectX 11.1 support is so-called blanket support and we can expose almost all the functions utilizing dx11_0 and dx11_1 hardware. We do not make any distinction between the two, since there are differences in hardware capabilities"
Second AAA game developer pretty much repeated the same story as the previous email comment:
"DirectX 11.1 is an incremental upgrade, and we support all the capabilities we need, regardless of dx11_0 or dx11_1 hardware. Remember DirectX 10 and different versions? They were also covered via software features. 90% of differences between 11.0 and 11.1 are software anyways."
We asked AMD about the Southern Islands, but AMD was very clear on the hardware support from the launch of the product - Southern Islands, Radeon HD 7000 Series is DirectX 11.1 compliant with full hardware feature level 11_1 (as listed on AMD Radeon HD 7970 Product Page). However, be warned that some AMD hardware from the 7000 series come only with the hardware feature level 11_0, as they are rebranded products from 6000 series of products (Northern Islands GPU architecture). It is rumored that the upcoming Kepler refresh (rumored GK112, GK114 and 117) will feature full hardware feature level 11_1 as well.