Construction and Evaluation of an Ultra Low Latency Frameless Renderer for VR.

© 2016 IEEE.Latency-the delay between a users action and the response to this action-is known to be detrimental to virtual reality. Latency is typically considered to be a discrete value characterising a delay, constant in time and space-but this characterisation is incomplete. Latency changes across the display during scan-out, and how it does so is dependent on the rendering approach used. In this study, we present an ultra-low latency real-time ray-casting renderer for virtual reality, implemented on an FPGA. Our renderer has a latency of 1 ms from tracker to pixel. Its frameless nature means that the region of the display with the lowest latency immediately follows the scan-beam. This is in contrast to frame-based systems such as those using typical GPUs, for which the latency increases as scan-out proceeds. Using a series of high and low speed videos of our system in use, we confirm its latency of 1 ms. We examine how the renderer performs when driving a traditional sequential scan-out display on a readily available HMO, the Oculus Rift OK2. We contrast this with an equivalent apparatus built using a GPU. Using captured human head motion and a set of image quality measures, we assess the ability of these systems to faithfully recreate the stimuli of an ideal virtual reality system-one with a zero latency tracker, renderer and display running at 1 kHz. Finally, we examine the results of these quality measures, and how each rendering approach is affected by velocity of movement and display persistence. We find that our system, with a lower average latency, can more faithfully draw what the ideal virtual reality system would. Further, we find that with low display persistence, the sensitivity to velocity of both systems is lowered, but that it is much lower for ours

Low Latency Rendering with Dataflow Architectures

The research presented in this thesis concerns latency in VR and synthetic environments. Latency is the end-to-end delay experienced by the user of an interactive computer system, between their physical actions and the perceived response to these actions. Latency is a product of the various processing, transport and buffering delays present in any current computer system. For many computer mediated applications, latency can be distracting, but it is not critical to the utility of the application. Synthetic environments on the other hand attempt to facilitate direct interaction with a digitised world. Direct interaction here implies the formation of a sensorimotor loop between the user and the digitised world - that is, the user makes predictions about how their actions affect the world, and see these predictions realised. By facilitating the formation of the this loop, the synthetic environment allows users to directly sense the digitised world, rather than the interface, and induce perceptions, such as that of the digital world existing as a distinct physical place. This has many applications for knowledge transfer and efficient interaction through the use of enhanced communication cues. The complication is, the formation of the sensorimotor loop that underpins this is highly dependent on the fidelity of the virtual stimuli, including latency. The main research questions we ask are how can the characteristics of dataflow computing be leveraged to improve the temporal fidelity of the visual stimuli, and what implications does this have on other aspects of the fidelity. Secondarily, we ask what effects latency itself has on user interaction. We test the effects of latency on physical interaction at levels previously hypothesized but unexplored. We also test for a previously unconsidered effect of latency on higher level cognitive functions. To do this, we create prototype image generators for interactive systems and virtual reality, using dataflow computing platforms. We integrate these into real interactive systems to gain practical experience of how the real perceptible benefits of alternative rendering approaches, but also what implications are when they are subject to the constraints of real systems. We quantify the differences of our systems compared with traditional systems using latency and objective image fidelity measures. We use our novel systems to perform user studies into the effects of latency. Our high performance apparatuses allow experimentation at latencies lower than previously tested in comparable studies. The low latency apparatuses are designed to minimise what is currently the largest delay in traditional rendering pipelines and we find that the approach is successful in this respect. Our 3D low latency apparatus achieves lower latencies and higher fidelities than traditional systems. The conditions under which it can do this are highly constrained however. We do not foresee dataflow computing shouldering the bulk of the rendering workload in the future but rather facilitating the augmentation of the traditional pipeline with a very high speed local loop. This may be an image distortion stage or otherwise. Our latency experiments revealed that many predictions about the effects of low latency should be re-evaluated and experimenting in this range requires great care

Exploring virtual reality in construction, visualization and building performance analysis

In the past two decades, the Architecture, Engineering and Construction (AEC) industry has investigated different approaches to improve communication among project parties, including Virtual reality (VR) however these approaches have not been widely adopted by the industry. Today, the tremendous advancements in technologies and computer hardware have potentially improved the current approaches and enabled a significant enhancement of user experience of Virtual reality (VR) devices. Based on that the researchers have conducted a review to investigate the global VR applications research in (AEC) community in 2015- 2017 to understand the status and the trend of immersive virtual reality (IVR) research in the world using these affordable devices. This paper also presents a result of an experiment to integrate three different types of AEC digital modeling data and proposed workflows for IVR applications in construction, visualization and building performance analysis. The experiment deals with construction simulation, rapid generation of the VR scene for existing building and airflow visualization. Several workflows investigated game engine and VR tools have been use

Low Latency Displays for Augmented Reality

The primary goal for Augmented Reality (AR) is bringing the real and virtual together into a common space. Maintaining this illusion, however, requires preserving spatially and temporally consistent registration despite changes in user or object pose. The greatest source of registration error is latency—the delay between when something moves and the display changes in response—which breaks temporal consistency. Furthermore, the real world varies greatly in brightness; ranging from bright sunlight to deep shadows. Thus, a compelling AR system must also support High-Dynamic Range (HDR) to maintain its virtual objects’ appearance both spatially and temporally consistent with the real world. This dissertation presents new methods, implementations, results (both visual and performance), and future steps for low latency displays, primarily in the context of Optical See-through Augmented Reality (OST-AR) Head-Mounted Displays, focusing on temporal consistency in registration, HDR color support, and spatial and temporal consistency in brightness: 1. For registration temporal consistency, the primary insight is breaking the conventional display paradigm: computers render imagery, frame by frame, and then transmit it to the display for emission. Instead, the display must also contribute towards rendering by performing a post-rendering, post-transmission warp of the computer-supplied imagery in the display hardware. By compensating in the display for system latency by using the latest tracking information, much of the latency can be short-circuited. Furthermore, the low latency display must support ultra-high frequency (multiple kHz) refreshing to minimize pose displacement between updates. 2. For HDR color support, the primary insight is developing new display modulation techniques. DMDs, a type of ultra-high frequency display, emit binary output, which require modulation to produce multiple brightness levels. Conventional modulation breaks low latency guarantees, and modulation of bright LEDs illuminators at frequencies to support kHz-order HDR exceeds their capabilities. Thus one must directly synthesize the necessary variation in brightness. 3. For spatial and temporal brightness consistency, the primary insight is integrating HDR light sensors into the display hardware: the same processes which both compensate for latency and generate HDR output can also modify it in response to the spatially sensed brightness of the real world.Doctor of Philosoph

TurboMouse: End-to-end Latency Compensation in Indirect Interaction

International audienceEnd-to-end latency corresponds to the temporal difference between a user input and the corresponding output from a system. It has been shown to degrade user performance in both direct and indirect interaction. If it can be reduced to some extend, latency can also be compensated through software compensation by trying to predict the future position of the cursor based on previous positions, velocities and accelerations. In this paper, we propose a hybrid hardware and software prediction technique specifically designed for partially compensating end-to-end latency in indirect pointing. We combine a computer mouse with a high frequency accelerometer to predict the future location of the pointer using Euler based equations

A Positional Timewarp Accelerator for Mobile Virtual Reality Devices

Mobile virtual reality devices are becoming more common, and yet their performance is still too low to be considered ideal. Frame rate and latency are two of the most important areas that should improve in order to provide a high-quality virtual reality experience. Meanwhile, positional tracking is improving the immersive experience of new mobile virtual reality devices by allowing users to physically move about in space and see their corresponding view matched in the virtual world. Timewarping is a technique that can improve the perceived latency and frame rate of virtual reality systems, but the positional variant of timewarping has proven to be difficult to implement on mobile devices due to the performance demands. A depth-informed positional time warp cannot be fully parallelized due to the depth test required for each pixel or group of pixels.This thesis proposes a positional timewarp hardware accelerator for mobile devices. The accelerator accepts a rendered frame and depth image and produces an updated frame corresponding to the user’s head position and orientation. The accelerator is compatible with existing deferred rendering engines for minimal modification of the software structure. Its execution time is directly proportional to the image resolution and is agnostic of the scene complexity. The accelerator’s size can be adjusted to meet the latency requirement for a given image resolution. It can be integrated into a system-on-chip or fabricated as a separate chip.Three examples are designed and simulated to show the performance potential of this accelerator architecture. The designs provide latencies of 15.43 ms, 11.58 ms and 9.27 ms for frame rates of 64.7, 86.4 and 107.9 frames per second, respectively. Although the visual side-effects may be insufficiently few to completely disregard the GPU’s frame rate, the accelerator can still improve the end-to-end positional latency and is also capable of substituting the GPU in the case of dropped frames

Towards Predictive Rendering in Virtual Reality

The strive for generating predictive images, i.e., images representing radiometrically correct renditions of reality, has been a longstanding problem in computer graphics. The exactness of such images is extremely important for Virtual Reality applications like Virtual Prototyping, where users need to make decisions impacting large investments based on the simulated images. Unfortunately, generation of predictive imagery is still an unsolved problem due to manifold reasons, especially if real-time restrictions apply. First, existing scenes used for rendering are not modeled accurately enough to create predictive images. Second, even with huge computational efforts existing rendering algorithms are not able to produce radiometrically correct images. Third, current display devices need to convert rendered images into some low-dimensional color space, which prohibits display of radiometrically correct images. Overcoming these limitations is the focus of current state-of-the-art research. This thesis also contributes to this task. First, it briefly introduces the necessary background and identifies the steps required for real-time predictive image generation. Then, existing techniques targeting these steps are presented and their limitations are pointed out. To solve some of the remaining problems, novel techniques are proposed. They cover various steps in the predictive image generation process, ranging from accurate scene modeling over efficient data representation to high-quality, real-time rendering. A special focus of this thesis lays on real-time generation of predictive images using bidirectional texture functions (BTFs), i.e., very accurate representations for spatially varying surface materials. The techniques proposed by this thesis enable efficient handling of BTFs by compressing the huge amount of data contained in this material representation, applying them to geometric surfaces using texture and BTF synthesis techniques, and rendering BTF covered objects in real-time. Further approaches proposed in this thesis target inclusion of real-time global illumination effects or more efficient rendering using novel level-of-detail representations for geometric objects. Finally, this thesis assesses the rendering quality achievable with BTF materials, indicating a significant increase in realism but also confirming the remainder of problems to be solved to achieve truly predictive image generation

Improving low latency applications for reconfigurable devices

This thesis seeks to improve low latency application performance via architectural improvements in reconfigurable devices. This is achieved by improving resource utilisation and access, and by exploiting the different environments within which reconfigurable devices are deployed. Our first contribution leverages devices deployed at the network level to enable the low latency processing of financial market data feeds. Financial exchanges transmit messages via two identical data feeds to reduce the chance of message loss. We present an approach to arbitrate these redundant feeds at the network level using a Field-Programmable Gate Array (FPGA). With support for any messaging protocol, we evaluate our design using the NASDAQ TotalView-ITCH, OPRA, and ARCA data feed protocols, and provide two simultaneous outputs: one prioritising low latency, and one prioritising high reliability with three dynamically configurable windowing methods. Our second contribution is a new ring-based architecture for low latency, parallel access to FPGA memory. Traditional FPGA memory is formed by grouping block memories (BRAMs) together and accessing them as a single device. Our architecture accesses these BRAMs independently and in parallel. Targeting memory-based computing, which stores pre-computed function results in memory, we benefit low latency applications that rely on: highly-complex functions; iterative computation; or many parallel accesses to a shared resource. We assess square root, power, trigonometric, and hyperbolic functions within the FPGA, and provide a tool to convert Python functions to our new architecture. Our third contribution extends the ring-based architecture to support any FPGA processing element. We unify E heterogeneous processing elements within compute pools, with each element implementing the same function, and the pool serving D parallel function calls. Our implementation-agnostic approach supports processing elements with different latencies, implementations, and pipeline lengths, as well as non-deterministic latencies. Compute pools evenly balance access to processing elements across the entire application, and are evaluated by implementing eight different neural network activation functions within an FPGA.Open Acces