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NVIDIA GTX 980 Review

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NVIDIA GTX 980 Closer Look:

Let's take a look at some of the specific technology implemented with the GTX 980. I'll let NVIDIA do the talking here, so enjoy!

DirectX 12: "Spanning devices ranging from PCs to consoles, tablets, and smartphones, Microsoft’s upcoming DirectX 12 API has been designed to have CPU efficiency significantly greater than earlier DirectX versions. One of the keys to accomplishing this is providing more explicit control over hardware—giving game developers more control of GPU and CPU functions. While the NVIDIA driver very efficiently manages resource allocation and synchronization under DX11, under DX12 it is the game developer’s responsibility to manage the GPU and GPU. Because the developer has an intimate understanding of their application’s behavior and needs, DX12 has the potential to be much more efficient than DX11 at the cost of some effort on the part of the developer. DX12 contains a number of improvements that can be used to improve the API’s CPU efficiency; we’ve announced that all Fermi, Kepler, and Maxwell GPUs will fully support the DX12 API."

"In addition, the DX12 release of DirectX will introduce a number of new features for graphics rendering. Microsoft has disclosed some of these features, at GDC and during NVIDIA’s Editor’s conference. Conservative Raster, discussed earlier in the GI section of this paper, is one such DX graphics feature. Another is Raster Ordered Views (ROVs,) which gives developers control over the ordering pixel shader operations. GM2xx supports both Conservative Raster and ROVs. The new graphics features included in DX12 will be accessible from either DX11 or DX12 so developers will be free to use these new features with either the DX11 or DX12 APIs on GPUs that implement the features in hardware."

 

Multi Frame Sampled AA or MFAA: "Game developers and GPU vendors are increasingly implementing more advanced forms of anti-aliasing (AA) to enhance image quality. GM2xx GPUs have a number of new features for much more flexible sampling, enabling further advancements in AA quality and efficiency. Today’s GPUs ship with fixed sample patterns for AA that are stored in ROM. When gamers select 2x or 4xMSAA for example, the pre-stored sample patterns are used. While many current games implement deferred, post-processed AA techniques such as FXAA or SMAA, there are still many others that continue to use traditional hardware-based multi-sample AA (MSAA). GM2xx GPUs support multi-pixel programmable sampling for rasterization, providing opportunities for more flexible and novel AA techniques to be implemented in the context of both deferred and conventional forward rendering."

"With programmable sample positions, the ROMs that were used to store the standard sample positions are replaced with RAMs. The RAMs may be programmed with the standard patterns, but the driver or application may also load the RAMs with custom positions which are free to vary from frame to frame or even within a frame. In a 16x16 grid per pixel, we have 256 different locations to choose from for each sample. We’ve also extended this programmable sample location support to span multiple pixels, so for example in 4x MSAA rendering, all 16 samples within a 2x2 pixel footprint can be located arbitrarily. This sample randomization can greatly reduce the quantization artifacts (like stair-stepping) that occur with more traditional forms of AA. These freely specified sampling positions may be used in the development of effective new algorithms."

"NVIDIA engineers have recently developed new AA algorithms that vary, in interleaved fashion, the sample patterns used per pixel either spatially in a single frame (where, for example, each successive pixel uses one of four different 4xAA sample patterns) or interleaved across multiple frames in time. Multi-Frame Sampled AA (MFAA) is a new AA technique that alternates AA sample patterns both temporally and spatially to produce the best image quality while still offering a performance advantage compared to traditional MSAA. The final result can deliver image quality approaching that of 8xAA at roughly the cost of 4xAA, or 4xAA quality at roughly the cost of 2xAA. Below we have a few images that show 4XMSAA implemented in BF4 and on the right the same scene with MFAA enabled."

 

 

DSR or Dynamic Super Resolution: "Thanks to rapidly falling LCD prices, the popularity of 4K displays has surged this year. But not all gamers want to spend the money on a new monitor. For the eye candy purists who don’t want to splurge but want to approximate the crisper visuals of a 4K panel, many have turned to the process of “downsampling.” This is where the GPU renders the game at a resolution higher than the screen can display, and then scales the image down to the native resolution on output to the user’s display. Downsampling require users to set up custom displays with the graphics driver control panel, and adjust various low-level display parameters to appear properly. So it’s not necessarily the friendliest way to improve image quality. Also, while downsampling can provide a significant improvement in image quality, artifacts are sometimes observed on textures and when certain post-processing effects are applied."

"To address the usability and quality issues, NVIDIA has developed a method called Dynamic Super Resolution. In principal, Dynamic Super Resolution works like traditional downsampling, but it has a simple on/off user control, and it uses a 13-tap Gaussian filter during the conversion to display resolution. The high-quality filter reduces or eliminates the aliasing artifacts experienced with the simple downsampling, which relies on a simpler box filter.Note that people often confuse downsampling (and now Dynamic Super Resolution) with the traditional Supersampling method of anti-aliasing. All three techniques render at higher resolutions internally, and then filter down to lower resolution for output. The difference is that downsampling and Dynamic Super Resolution actually have the game render at the higher resolution, so the game believes it’s running on a higher resolution display, and the GPU then filters and samples down. The process should work with most games well, aside from some issues with visibility of onscreen game controls being displayed on lower resolution monitors."

"With supersampling, the game still renders at a particular resolution—say 1920x1080—and the GPU upsamples that resolution without the game’s knowledge, and then filters back down. This can cause issues with newer games that use post-processing effects, or are expecting the full rendering process to be at a given resolution set by the game itself. Dynamic Super Resolution can be found in the control panel of our Release 343 driver, as well as GeForce Experience, where we provide Optimal Playable Settings (OPS) for Dynamic Super Resolution for today’s hottest games. While it’s compatible with all GeForce GPUs, the best performance can be seen when using a GeForce GTX 980."

"Going forward we could potentially use Maxwell’s more advanced sampling control features, like programmable sample positions and interleaved sampling, to further improve Dynamic Super Resolution for owners of GM2xx GPUs." In the image below you can get a feel for what this technology can do for image quality when you compare the grass on the right and left sides of the image."

 

Last but not least is Voxel Global Illumination or VXGI: "Correct modelling of lighting is the most computationally difficult problem in graphics, and with Maxwell, our objective was to make an enormous leap forward in the capability of the GPU to perform near-photo-real lighting calculations in real time. In the real world, all objects are lit by a combination of direct light (photons that travel directly from a light source to illuminate an object) and indirect light (photons that travel from the light source, hit one object and bounce off of it and then hit a second object, thus indirectly illuminating that object). “Global illumination” (GI) is a term for lighting systems that model this effect. Without indirect lighting, scenes can look harsh and artificial. However, while light received directly is fairly simple to compute, indirect lighting computations are highly complex and computationally heavy. Because it’s a computationally expensive lighting technique (particularly in highly detailed scenes), GI has been primarily used to render complex CG scenes in movies using offline GPU rendering farms."

"While some forms of GI have been used in many of today’s most popular games, their implementations have relied on pre-computed lighting. These “prebaked” techniques are used for performance reasons; however, they require additional artwork, as the desired lighting effects must be computed beforehand. Because prebaked lighting is not dynamic, it’s often difficult or impossible to update the indirect light sources when in-game changes occur; say for instance an additional light source is added or something in the scene moves or is destroyed. Prebaked indirect lighting models the static objects of the scene, but doesn’t properly apply to the animated characters or moving objects.In 2011, NVIDIA engineers developed and demonstrated an innovative new approach to computing a fast, approximate form of global illumination dynamically in real time on the GPU. This new GI technology uses a voxel grid to store scene and lighting information, and a novel voxel cone tracing process to gather indirect lighting from the voxel grid. NVIDIA’s Cyril Crassin describes the technique in his paper on the topic and a video from GTC 2012 is available here. Epic’s ‘Elemental’ Unreal Engine 4 tech demo from 2012 used a similar technique."

 

"Since that time, NVIDIA has been working on the next generation of this technology—VXGI—that combines new software algorithms and special hardware acceleration in the Maxwell architecture. To understand how voxel global illumination works, it is helpful to first understand voxels. The term “voxel” is related to “pixel.” Whereas a pixel represents a 2D point in space, a voxel represents a small cube (a volume) of 3D space. To perform global illumination, we need to understand the light emitting from all of the objects in the scene, not just the direct lights. To accomplish this, we dice the entire 3D space of the scene in all three dimensions, into small cubes called voxels. “Voxelization” is the process of determining the content of the scene at every voxel, analogous to “rasterization” which is the process of determining the value of a scene at a given 2D coordinate."

 

Now let's move on to determine how the GTX 980 performs in a head to head competition.

Source: NVIDIA GTX 980 whitepaper




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