Chapter 5 - Performance Estimation and System Tuning in Virtual Reality Systems PDF

DESIGNING AND BUILDING VIRTUAL ENVIRONMENTS Chapter five : Performance Estimation and System Tuning in Virtual Reality Systems Ala Shakhatreh Introduction to Performance Estimation and Tuning  performance estimatio...

DESIGNING AND BUILDING VIRTUAL ENVIRONMENTS Chapter five : Performance Estimation and System Tuning in Virtual Reality Systems Ala Shakhatreh Introduction to Performance Estimation and Tuning  performance estimation is the process of assessing and predicting a system’s capacity to handle the demands of immersive experiences.  The goal of performance estimation is to identify potential limitations or bottlenecks early, allowing developers to make necessary adjustments to ensure an optimal balance between visual fidelity and real- time responsiveness. It’s essential for maintaining immersion without overloading the system, which could lead to issues like lag or motion sickness. Ala Shakhatreh Introduction to Performance Estimation and Tuning  Tuning is the process of optimizing these system parameters to maintain high performance without sacrificing visual quality or user immersion. This includes adjusting elements like graphics quality, object detail levels, and special effects to achieve a balance between realism (presence) and smooth functionality. Ala Shakhatreh The Presence and Performance Trade-off ❑ Presence in virtual reality (VR) refers to the user's sensation of "being there" inside the virtual environment. ❑ Presence is influenced by factors such as:  Realism of Graphics: High-quality, lifelike visuals help convince the brain that the environment is authentic.  Responsiveness: Low latency and smooth interactions make movements feel natural, which reinforces immersion.  Sensory Feedback: Elements like 3D audio, haptic feedback, and spatial tracking contribute to a multi-sensory experience that supports the illusion of presence. ❑ When VR systems achieve strong presence, users feel more connected to the virtual environment, which leads to more engaging and effective experiences. Ala Shakhatreh The Presence and Performance Trade-off ❑ VR systems face significant challenges with processing power and frame rates because they must render complex 3D environments and respond to user actions in real time to maintain immersion.  Challenges: 1. High Frame Rate Requirements: VR requires frame rates of at least 90 frames per second (fps) per eye to avoid motion sickness and ensure smooth visuals. 2. Real-Time Rendering: VR systems need to process and render high-quality, realistic 3D graphics instantly as the user moves. Ala Shakhatreh The Presence and Performance Trade-off 3. High-Resolution Displays: VR displays often have high resolutions to create detailed visuals and reduce the "screen door" effect (visible gaps between pixels). 4. Latency and Responsiveness: VR systems must have extremely low latency (time delay between user action and system response) to maintain immersion. 5. Resource Demands of Special Effects: Elements like realistic lighting, shadows, reflections, and physics-based effects enhance immersion but require considerable processing power. Balancing these features with performance is crucial, as too many effects can reduce frame rates and affect responsiveness. Ala Shakhatreh The Presence and Performance Trade-off ❑ Solution : To address these challenges, VR systems often use optimization techniques like Level of Detail (LOD) models, efficient rendering practices, and specialized VR hardware to ensure a balance between visual quality and performance. Ala Shakhatreh Tuning with Level of Detail (LOD) Models ❑ Level of Detail (LOD) models are optimization techniques used in 3D graphics, including VR, to manage the complexity of objects based on their distance from the viewer. ❑ With LOD, objects close to the viewer are rendered in high detail, while objects farther away are shown with simplified, lower-detail versions. ❑ This approach reduces the number of polygons or texture details needed for distant objects that the user isn't focused on, saving computational resources without significantly affecting perceived quality. Ala Shakhatreh Tuning with Level of Detail (LOD) Models Ala Shakhatreh Tuning with Level of Detail (LOD) Models Table 5.1 shows performance test results in terms of the average frame rates for each chosen LOD. Although results show the expected trivial fact that more complex models produce lower frame rates, we observe that the variances in the frame rates are not linear. For instance, if we were to select a 2-LOD-mix for the case of 50 ships, we might choose L2 and L3, because they have higher details at a similar cost versus L1 and L4, This table illustrates how using simpler LODs can help respectively. maintain smoother performance, especially when managing a large number of objects in a VR environment. Ala Shakhatreh Presence and Special Effects in Spiral Development  special effects are added to the VR environment. These effects—such as lighting, shadows, reflections, and environmental elements like fog or particle effects— significantly enhance presence by making the virtual world more immersive and realistic.  Graphics cards, or GPUs (Graphics Processing Units), and specialized VR hardware play a critical role in enhancing the performance of VR systems , implementing a simple effect is very simple because of the built-in capabilities of today’s graphics hardware. And because it is hardware- supported, there is not much performance drop Ala Shakhatreh Fog Effect for Depth Perception ❑ The Fog Effect is a visual technique used in VR to enhance depth perception and scene immersion by creating a natural sense of distance. By adding a gradient or haze that becomes denser with distance. ❑ Fog helps users gauge distances by gradually obscuring objects as they get farther away. This creates a layering effect, where objects in the foreground are clearer than those in the background, allowing users to perceive depth more naturally. Ala Shakhatreh Fog Effect for Depth Perception Example of global fog, demonstrating both distance and height-based fog Ala Shakhatreh Using Images and Textures for Efficient Modeling: ❑ Textures are a rectangular pieces of images applied to the surface of 3D models to simulate fine details like color, patterns, and materials. Instead of adding more geometry (such as extra vertices and polygons), textures "paint" visual details onto an object, creating the illusion of complexity. ❑ For example: A brick wall texture can show every individual brick, including cracks and weathering, without modeling each brick as a separate 3D object. A wood grain texture on a table can replicate natural wood patterns and imperfections without increasing the table’s polygon count. Ala Shakhatreh Using Images and Textures for Efficient Modeling: Textures enable VR developers to achieve visually rich environments with minimal impact on system performance. By adding visual complexity through textures rather than geometry, VR applications can maintain smooth, high-frame-rate experiences that are essential for geometric model texture mapped immersion. Ala Shakhatreh Using Images and Textures for Efficient Modeling: There are many ways a texture can be pasted upon the object surface. In the simplest case, a texture is applied to a planar surface. The process is depicted in Figure 5.1. Ala Shakhatreh Using Images and Textures for Efficient Modeling: First, the user must specify the corresponding texture pixels (texel) for the three vertices. The three vertices would be projected to the display screen, and during the scan conversion process to render the interior of the projected triangle on the screen, the right color must be brought from the corresponding place in the texture. The final rendered color at that pixel is a function of this texel color and other parameters related to lighting and shading (e.g., viewpoint, triangle/surface normal, shading model, etc.). In order to map the pixels in the screen space to the texture space, each space is parameterized using unified coordinates as shown in Figure 5.2. Ala Shakhatreh Using Images and Textures for Efficient Modeling: ❑ Types of Texture Mapping: Planar Mapping: Applies textures to flat surfaces. Cylindrical and Spherical Mapping: Wraps textures around curved surfaces, like cylinders or spheres. Environment Mapping: Adds reflections, ideal for shiny objects. Bump Mapping: Simulates surface protrusions for added depth. Ala Shakhatreh Using Images and Textures for Efficient Modeling: In addition to modeling the complex surface properties of objects, textures can be used to represent the object itself , Billboards and Moving Textures (Sprites) are texture-based techniques which These techniques often leverage multiple textures or animated sequences to add dynamic effects or represent objects and entire scenes more efficiently. ❖ Billboards are often used for (rotationally symmetric) objects : ❖ Case (a) uses multiple textures arranged around an axis to simulate 3D appearance from different angles. ❖ Case (b) uses a single texture that rotates to always face the viewer, maintaining the illusion of depth without multiple textures. Ala Shakhatreh Using Images and Textures for Efficient Modeling: Ala Shakhatreh Using Images and Textures for Efficient Modeling: ❖ Sprites (Moving Textures) ▪ involve displaying a series of images (textures) one after another in quick succession to create the illusion of motion (e.g., fire, explosion). ▪ Common in VR and gaming for character animation and special effects. Ala Shakhatreh Using Images and Textures for Efficient Modeling: ❑ Advanced Texture Applications in Scene Modeling: Background Texturing : Textures can represent large scene elements like the sky or mountains. For instance, in the QuickTime VR approach by Chen [Che95], a panoramic image is captured and stored as a cylindrical environment map, and depending on the viewer location and viewing direction, the appropriate part of the environment map is retrieved and rendered to the user (see Figure 5.5). Ala Shakhatreh Using Images and Textures for Efficient Modeling: In the approach called ‘‘Tour into the Picture’’ by Horry et al. [Hor97], a static image is split up into regions according to the location of the vanishing point, and each of the pieces is pasted upon the interior of large rectangular box (see Figure 5.6). Note : Object and scene modeling (and even behavior modeling) can be made easier by employing these texture techniques in a creative way. Ala Shakhatreh Adding the Wave Effect in VR ❑ The wave effect creates the illusion of a surface that moves or ripples, often applied to water, glass, or liquid surfaces in VR environments. Adds realism and depth to scenes, making them more immersive by adding visual dynamics. ❑ Traditional vs. Animated Sea Surface Static Approach: A single, large, static textured polygon representing the sea. Dynamic Approach: Using rotating of a sequence textures (four in this example) to create the illusion of waves. Mimics natural sea movement by regularly switching through the texture images. Ala Shakhatreh Adding the Wave Effect in VR ❑ Implementation of the Wave Effect Simple Rotation Logic: Four texture images cycle in sequence, creating a "wave" appearance. This simple animation trick enhances realism without heavy computation.  Wind Velocity and Wave Height: Adjusts the rate of texture cycling to match wind and wave conditions. Ala Shakhatreh Adding the Wave Effect in VR ❑ simple other wave patterns: ❖ Sine Wave Patterns: By applying a sine wave function to the vertices of a surface, you can make the surface appear to ripple. ❖ Texture Animation: it is animating a wave texture on the surface. This can be done by using animated shader effects in Unity, which only requires a texture to be scrolled or distorted over time. ❖ Vertex Displacement: Adjusting the position of vertices over time based on wave algorithms (e.g., sine or cosine functions) can create more dynamic wave motions. This method is commonly used for water surfaces in VR because it’s visually effective without requiring complex computations. Ala Shakhatreh Adding the Wave Effect in VR Ala Shakhatreh