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NVIDIA GeForce GTX 980 Ti Review

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NVIDIA GeForce GTX 980 Ti Closer Look:

When the GTX 980 launched, NVIDIA improved the feature set on its Maxwell-based video cards with added technologies implemented on the new releases, as well as with the cards it was putting out going forward with DX12 support, MFAA, DSR, VXGI, and now Virtual Reality support. I'll let NVIDIA do the talking here so the details do not get lost in translation - 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."

"DirectX 12 supports more than just these API enhancements. In addition, DirectX 12 also includes support for new graphics rendering features that will enable developers to produce games with richer graphics effects. Two DX12 feature levels are supported: Feature Level 12.0 and Feature Level 12.1. Feature Level 12.0 supports tiled resources, bindless textures, and typed UAV access. Feature Level 12.1 is a more advanced implementation that includes support for all 12.0 features as well as conservative raster and raster ordered views. Additionally, GM2xx GPUs support an additional graphics feature: volume tiled resources. If you recall, with tiled resources only the portions of the textures that are required for rendering are stored in the GPU’s memory. Tiled Resources works by breaking textures down into tiles, and the application determines which tiles might be needed and loads them into video memory. This feature can allow game developers to produce higher fidelity graphics with less memory. Previously, tiled resources were limited to 2D objects only. With volume tiled resources, this capability is extended to volume (3D) textures also."



"Conservative Raster is one of the key requirements needed for DirectX 12 Feature Level 12.1. Conservative Raster provides a more accurate method for determining whether or not a pixel is covered, at the cost of being more expensive in terms of performance. In traditional rasterization, a triangle is considered covered if a pixel covers a specific sample point within that pixel, for example, the center of the pixel in the example below. With conservative rasterization rules on the other hand, a pixel is considered covered if any part of the pixel is covered by any part of the triangle. By providing hardware acceleration for conservative raster, the GPU can perform these calculations more efficiently. This in turn enables game developers to employ novel new approaches to enhance image quality. For example, conservative raster can be used to produce ray-traced shadows. In the example below, the ray-traced shadows are free of the aliasing found in the other examples:"



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."


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."


Virtual Reality:

"Virtual reality (VR) is one of the hottest topics in the gaming industry today. Oculus has announced plans to release a commercial version of their Oculus Rift VR headset to consumers by the end of the year, and similarly Valve has just announced plans to partner with HTC to bring their VR headset to the market by the end of 2015 as well. NVIDIA is working with hardware and software vendors in the VR space to ensure that gamers can seamlessly enjoy VR on the GeForce platform."

"In order to provide an immersive VR experience, VR must overcome a number of challenges. One of these is latency: any perceived delays between the user moving their head and the display responding accordingly can throw off the VR experience, potentially causing the user to get motion sickness. To reduce this latency, NVIDIA’s VR Direct software supports a feature called asynchronous time warp. With asynchronous time warp, the last scene rendered by the GPU is shifted based on the latest head position info taken from the VR sensor. This saves time, as the GPU doesn’t have to re-render the entire scene from scratch. NVIDIA provides driver level support for setting context priority, allowing developers to implement asynchronous time warp in their games and apps."

"Besides latency, another major obstacle that must be overcome to provide an immersive VR experience is performance; not only is a high frame rate needed, it’s also important that the frames are delivered to the user’s eye in a smooth fashion. Therefore many gamers who want to play the most demanding games with maximum eye candy will want to combine two GeForce cards for SLI. To ensure the best experience possible we’ve developed VR SLI. VR SLI allows game developers to assign a specific GPU to each eye to scale performance and reduce latency: the display responsible for the left eye will behandled by one GPU, while the second GPU will be responsible for the display on the right eye. This solution provides lower latency and ultimately better performance for the user. An alpha driver that combines VR SLI and asynchronous time warp is now in the hands of select partners including Epic, Crytek, Valve, and Oculus. A public driver will also be released in the coming months."




Source: NVIDIA GTX 980 and GTX 980 Ti documentation

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