How does AltspaceVR render three Js in unit
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During natural viewing, the human visual system relies on multiple sources of information, or "cues," to interpret 3D shapes and the relative positions of objects. Some cues rely only on a single eye, or monocular cue, including:
Other cues require both eyes - they are binocular cues. These include: Other cues rely on both eyes, or binocular cues, and include:
- Convergence - essentially the relative rotations of the eyes required to look at an object
- Parallax: the pattern of differences between the projections of the scene on the back of the two eyes
To ensure maximum comfort on head-mounted displays, it's important to create and present content in a way that mimics cues in the natural world. From a physical perspective, it's also important to design content that doesn't require fatiguing motions of the neck or arms. In this article, we'll go over key considerations to keep in mind to achieve these goals.
To view objects clearly, humans must accommodate, or adjust their eyes' focus, to the distance of the object. At the same time, the rotation of both must At the same time, the rotation of both eyes must converge to the object's distance to avoid seeing double images. In natural viewing, convergence and accommodation are linked , vergence and accommodation are linked. When you view something near, for example, a house fly close to your nose, your eyes cross and accommodate to a near point ke starts at about 6 m or further), the lines of sight of your eyes parallel, and the lenses of your eyes accommodate to infinity. Conversely, if you view something at optical infinity (roughly starting at 6 m or farther for normal vision), your eyes' lines of sight become parallel and your eyes' lenses accommodate to infinity.
With most head-mounted displays, users always accommodate to the focal length of the display (to get a sharp image) but converge to the distance of the object of interest (to get a single image) will always accommodate to the focal distance of the display to get a sharp image, but converge to the distance of the object of interest to get a single image. As users accommodate and converge at different distances, the natural relationship between the two cues is broken When users accommodate and converge to different distances, the natural link between the two cues is broken, leading to visual discomfort or fatigue.
Guidance for holographic devices
HoloLens displays are fixed at an optical distance approximately 2.0 m away from the user. Users must always accommodate to approximately 2 m to maintain a sharp image in the device .Users must always accommodate near 2.0 m to maintain a clear image in the device. App developers can guide the convergence of users 'eyes by positioning content and holograms at different depths. App developers can guide where users' eyes converge by placing content and holograms at various depths. Discomfort resulting from the conflict of convergence and accommodation can be avoided or minimized by keeping content that users' eyes converge on as close as possible to 2.0 m. Discomfort from the vergence-accommodation conflict can be avoided or minimized by keeping content to which users converge as close to 2.0 m as possible. For example, in a scene with lots of depth, place the areas of interest near 2.0 m from the user when possible When content cannot be placed near 2.0 m, discomfort from the vergence-accommodation conflict is greatest when the user's gaze switches back and forth between different distances. In other words, it is much more pleasant to look at a standing hologram that remains 50 cm away than to look at a hologram 50 cm away that In other words, it's much more comfortable to look at a stationary hologram that stays 50 cm away than to look at a hologram 50 cm away that moves toward and away from you over time.
Optimal distance from the user for positioning hologramsOptimal distance for placing holograms from the user
Best practices for HoloLens (1st gen) and HoloLens 2
For maximum comfort the optimal range for the placement of holograms is between 1.25 m and 5 m.For maximum comfort, the optimal zone for hologram placement is between 1.25 m and 5 mAt all costs, designers should try to structure content scenes in a way that encourages users to interact 1 meter or more away from the content (e.g., by adjusting content size and default placement parameters). In every case, designers should attempt to structure content scenes to encourage users to interact 1 m or farther away from the content (for example, adjust content size and default placement parameters).
While it may occasionally be necessary to display content closer than 1 m away, we do not recommend displaying holograms closer than 40 cm away. Rather, we recommend Hide content at 40 cm and place a clipping plane for rendering at 30 cmAlthough content may occasionally need to be displayed closer than 1 m, we recommend against ever presenting holograms closer than 40 cm. Thus, we recommend starting to fade out content at 40 cm and placing a rendering clipping plane at 30 cm to avoid any nearer objects.
Objects that move in depth are more likely than stationary objects to produce discomfort because of the vergence-accommodation conflict Similarly, requiring users to rapidly switch between near-focus and far-focus (for example, because of a pop-up hologram requiring direct interaction) can cause visual discomfort and fatigue.Special care should be taken to minimize the frequency of these two points for users: viewing content with changing depths of space and quickly switching focus between near and far holograms.Extra care should be taken to minimize how often users are: viewing content that is moving in depth; or rapidly switching focus between near and far holograms.
Other considerations for HoloLens 2 and near interaction distances
When designing content for direct (close) interaction in HoloLens 2 or In all applications where content has to be placed closer than 1 m away, special attention should be paid to the comfort of the userWhen designing content for direct (near) interaction in HoloLens 2, or In any applications where content must be placed closer than 1 m, extra care should be taken to ensure user comfortThe odds of discomfort due to the vergence-accommodation conflict increase exponentially with decreasing viewing distance possibly more blurring. As a result, testing content both within the range of optimal hologram placement and closer (less than 1.0 m down to the clipping plane) is a good practice to ensure that it is sharp and comfortable to view. Additionally, users may experience increased blurriness when viewing content at near interaction distances, so we recommend testing content rendered both within the zone of optimal hologram placement and closer (less than 1.0 m down to the clipping plane) to ensure it remains clear and comfortable to view.
We recommend setting up a "depth budget" for apps based on the length of time a user is expected to view content that is nearby (closer than 1.0 m) and that moves with varying depths of space.We recommend creating a “depth budget” for apps based on the amount of time a user is expected to view content that is near (less than 1.0 m) and moving in depthAn example is to avoid placing the user in those situations more than 25% of the time. If the budget is exceeded, we recommend careful user testing to make sure If the depth budget is exceeded, we recommend careful user testing to ensure it remains a comfortable experience.
In general, we also recommend careful testing to ensure any interaction requirements (for example , velocity of movement, reachability, etc.) at near interaction distances remain comfortable for users.
Guidance for immersive devices
For immersive devices, the guidance and best practices for HoloLens still applies, but the specific values for the Zone of Comfort are shifted depending on the focal distance to the display. In general, the focal distances to these displays are between 1.25m-2.5m. Avoid When in doubt, avoid rendering objects of interest too near to users and instead try to keep most content 1 m or farther away.
Interpupillary distance and vertical offset
When viewing digital content on head-mounted displays (HMD), the position of a viewer's eyes based On the display position of digital content is critical. Specifically, both interpupillary distance (IPD) and vertical offset (VO) are important for comfortable viewing of digital content in HMDs.
PD refers to the distance between the pupils, or centers, of an individual's eyes. VO refers to the potential vertical offset of digital content presented to each eye relative to the horizontal axis of the eyes VO refers to the potential vertical offset of digital content shown to each eye relative to the horizontal axis of the viewer's eyes (notably, this is NOT the same as horizontal offset, or binocular disparity). Mismatching one or both of these factors to the individual user can add to the discomfort caused by the conflict of convergence and accommodation, but it can also cause discomfort if the KA conflict has been minimized (e.g. for content that is displayed at a focal distance of 2.0 m from the HoloLens rden) .Mis-matching either or both of these factors to an individual user can worsen the effects of discomfort caused by vergence-accommodation conflict, but it can even cause discomfort when VA conflict is minimized (for example, for content displayed at the 2.0 -m focal distance of the HoloLens).
Guidance for holographic devices
HoloLens (1st generation) HoloLens (1st gen)
For HoloLens (1st gen), IPD is estimated and set during device calibration. For new users of a device that has already been set up, calibration must be performed, or the PD must be set manually.For new users to an already set up device, calibration must be run or IPD must be set manually.VO depends solely on the adaptation of the device.VO depends wholly on device fit.In particular, to minimize Specifically, to minimize VO, the device needs to be resting on a user's head such that the displays are level with the axis of his / her eyes.
HoloLens 2HoloLens 2
For HoloLens 2, IPD is estimated and set during eye / device calibration. For new users of a device that has already been set up, calibration must be performed to ensure that the For new users to an already set up device, calibration must be run to ensure IPD is set correctly. VO is accounted for automatically in HoloLens 2.
Guidance for immersive devices
Immersive HMDs for Windows Mixed Reality have no automatic calibration for PD or VO. Windows Mixed Reality immersive HMDs have no automatic calibration for IPD or VO. The PD can be set manually in software (under the settings in the Mixed Reality portal, see calibration) . Some HMDs also have a manual slider that allows the lens spacing to be adjusted to a comfortable position, a position roughly the same as the user's PD. IPD can be set manually in software (under Mixed Reality Portal settings, see calibration), or Some HMDs have a mechanical slider that allows the user to adjust the spacing of the lenses to a comfortable position that roughly matches their IPD.
Mixed reality apps are unique because users can move freely in the world and interact with virtual content like as though they were real objects. To maintain this impression, it's critical to render holograms so they appear stable in the world and animate smoothly. Achieving this goal is supported by rendering at a minimum of 60 frames per second (FPS). Rendering at a minimum of 60 frames per second (FPS) helps achieve this goal. Some mixed reality devices support this Render at frame rates higher than 60 FPS, and higher frame rate rendering is recommended for these devices for the best user experience There are some Mixed Reality devices that support rendering at framerates higher than 60 FPS and for these devices it's recommended to render at the higher framerates to provide an optimal user experience.
Deeper insightsDiving deeper
To draw holograms to look, like they're stable in the real or virtual world, apps need to render images from the user's position. Since images take time to render, HoloLens and other Windows Mixed Reality devices predict where a user's head will be when the images appear in the displays other Windows Mixed Reality devices predict where a user's head will be when the images are shown in the displays. This prediction algorithm is an approximation. Windows Mixed Reality algorithms and hardware adjust the rendered image so that that the deviation between the predicted head position and the actual head position is taken into account. Windows Mixed Reality algorithms and hardwa re adjust the rendered image to account for the discrepancy between the predicted head position and the actual head position. This process makes the image seen by the user as being rendered from the correct location and holograms to feel stable by the user appear as if it were rendered from the correct location, and holograms feel stable. Updates work best for small changes in head position and may not fully account for some differences in the rendered image, such as those caused by motion parallax updates work best for small changes in head position, and they can't completely account for some rendered image differences, like those caused by motion-parallax.
By using at least a frame rate of 60 FPS for rendering, you are promoting two effects that favor stable holograms:By rendering at a minimum frame rate of 60 FPS, you're doing two things to help make stable holograms:
- Reducing the appearance of judder, which is characterized by uneven motion and double images. Faster movement of holograms and lower rendering rates go hand in hand with increased vibration. Faster hologram motion and lower render rates are associated with more pronounced judder.Therefore, striving to always maintain 60 FPS (or your device's maximum render rate) will help avoid judder for moving holograms.
- Minimizing the overall latency.In an engine with a game thread and a render thread running at 30 FPS can result in an additional 33.3 ms of latency running in lockstep, running at 30FPS can add 33.3 ms of extra latency. By reducing latency, this decreases prediction error, and increases hologram stability.
Performance analysisPerformance analysis
There are different tools that can be used to benchmark your application frame rate such as: There are different tools that can be used to benchmark your application frame rate such as:
- Visual Studio Graphics Debugger
- Integrated profilers of 3D engines, e.g. B. der Frame Debugger in UnityProfilers built into 3D engines such as the Frame Debugger in Unity
Self-motion and user locomotion
The only limitation is the size of your physical space - if you want to allow users to move farther in the virtual environment than they can in their real space, some form of purely virtual movement must be implemented your physical space; if you want to allow users to move farther in the virtual environment than they can in their real rooms, then a form of purely virtual motion must be implemented However, sustained virtual motion that doesn't match the user's real, physical motion can often induce motion sickness. This result is due to the contrast between the visual cues for the proper movement from the virtual world and the vestibular indications for proper motion resulting from the real world This outcome is because the visual cues for self-motion from the virtual world conflicting with the vestibular cues for self-motion coming from the real world.
Fortunately, there are tips for implementing user locomotion that can help avoid the issue:
- Always give the user control over their movements; unexpected proper movement is problematicAlways put the user in control of their movements; unexpected self-motion is problematic
- Humans are sensitive to the direction of gravity. Therefore, non-user-initiated vertical motions especially should be avoided.
Guidance for holographic devices
One method to allow the user to move to another location in a large virtual environment is to give the impression they're moving a small object in the scene. This effect can be achieved as follows:
- Provide an interface where the user can select a spot in the virtual environment where they want to move.
- Upon selection, shrink the scene rendering down to a disk around the desired spot.
- While keeping the spot selected, allow the user to move it as though it were a small object. Then the user can make the selection The user can then move the selection close to their feet.
- Upon deselection, resume rendering the entire scene.
Guidance for immersive devices
The aforementioned holographic device approach doesn't work as well with immersive devices because it requires the app to render a large black space or some other standard environment while the "slice" is being moved. The preceding holographic device approach doesn't work as well in an immersive device because it requires the app to render a large black void or another default environment while moving the “disk.” This procedure destroys the illusion of immersion. This treatment disrupts one's sense of immersion. A trick for changing the user's location with immersive headsets is the “blinking” method. One trick for user locomotion in an immersive headset is the “blinking” approach. This implementation gives the user control over his movement and gives a brief impression of movement, which is so short that the user can is less likely to feel disoriented by the purely virtual proper movement: This implemen tation provides the user with control over their motion and gives a brief impression of movement, but makes it so brief that the user is less likely to feel disoriented by the purely virtual self-motion:
- Provide an interface where the user can select a spot in the virtual environment where they want to move.
- Upon selection, begin a rapid simulated (100 m / s) motion towards that location while quickly fading out the rendering.
- Fade the rendering back in after finishing the translation.
In first-person-shooter video games, head-up displays (HUDs) permanently show information such as the health of the player, map details and inventories directly on the screen. persistently present information such as player health, mini-maps, and inventories directly on the screen. HUD's work well to keep the player informed In mixed reality experiences, HUDs have the potential to cause significant discomfort and must be adapted to the more immersive context. In particular, HUDs that are rigidly tied to the player's head posture are more likely to cause discomfort. HUDs that are rigidly locked to the user’s head orientation are likely to produce discomfort. If an app requires a HUD, we recommend binding to the body If an app requires a HUD, we recommend body locking rather than head locking. This behavior can be implemented as a set of displays that immediately move with the user, but do not rotate the user's head until a threshold for rotation is reached. This treatment can be implemented as a set of displays that immediately translate with the user, but don't rotate with the user's head until a threshold of rotation is reached. As soon as this degree of rotation is reached, the HUD can realign itself to show the user the information in his field of view Once that rotation is achieved, the HUD may reorient to present the information within the user's field of view. Avoid implementing 1: 1 HUDs relative to the user's head movements rotation and translation based on the user's head motions.
Optimal text legibility can help reduce eye strain and maintain user comfort, especially in applications or scenarios that require users to read while using an HMD. Text legibility depends on various factors including:
- Display properties such as pixel density, brightness, and contrast.
- Lens properties like chromatic aberration
- Text / font properties such as weight, spacing, serifs, and font / background color.
In general, we recommend testing specific applications for legibility and making font sizes as large as possible for a comfortable experience . You can find more detailed guidance for holographic and immersive devices in our Typography and Text in Unity pages.
Holographic frame considerations
For mixed reality experiences with large objects or many objects, it's crucial to consider how much head and neck movement is necessary to interact with content. The user interfaces can be divided into three categories in terms of head movement: Experiences can be divided into three categories in terms of head movement:
- Horizontal (from side to side)Horizontal (side to side)
- Vertical (up and down)Vertical (up and down)
- Immersive (both horizontally and vertically)Immersive (both horizontal and vertical)
Whenever possible, limit most interactions to either the horizontal or vertical category. When possible, limit most interactions to either horizontal or vertical categories, ideally with most experiences taking place in the center of the holographic frame while the user's head is in a neutral position. Avoid interactions that require the user to constantly shift their view to an unnatural head position (such as looking up frequently to access an important menu) that cause the user to constantly move their view to an unnatural head position (for example, always looking up to access a key menu interaction).
The optimal range for content is between 0 degrees and 35 degrees below the horizonOptimal region for content is 0 degrees to 35 degrees below horizon
Horizontal head movement is more for frequent interactions, while vertical movements should be reserved for uncommon events. For example, a user interface that has a long horizontal timeline For example, an experience involving a long horizontal timeline should limit vertical head movement for interactions (like looking down at a menu).
Consider encouraging full-body movement, rather than just head movement, by placing objects around the user's space. For interfaces with moving or large objects, should Experiences with moving objects or large objects should pay special attention to head movement, especially where they require frequent movement along both the horizontal and vertical axes.
To avoid eye and neck strain, content should be designed so that excessive eye and neck movements are avoided.
- Avoid You view angles beyond 10 degrees above the horizon (vertical movement)Avoid Gaze angles more than 10 degrees above the horizon (vertical movement)
- Avoid You viewing angles beyond 60 degrees below the horizon (vertical movement)Avoid Gaze angles more than 60 degrees below the horizon (vertical movement)
- Avoid You rotate the neck more than 45 degrees from the central position (horizontal movement)Avoid neck rotations more than 45-degrees off-center (horizontal movement)
The optimal (resting) gaze angle is considered between 10-20 degrees below horizontal as the optimal (resting) gaze angle is considered between 10-20 degrees below horizontal As the head tends to tilt downward slightly, especially during activities.
Muscle fatigue can accumulate when users are expected to keep a hand raised throughout the duration of an experience It can also be fatiguing to require the user to repeatedly make air tap gestures over long durations. We therefore recommend avoiding experiences requiring constant, repeated gesture input. These goals can be achieved by incorporating short breaks or offering a mixture of gesture and speech input to interact with the app.
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