8.2 Advanced lighting and global illumination techniques
4 min read•august 7, 2024
Advanced lighting and techniques take real-time rendering to the next level. They simulate complex light interactions, creating more realistic and immersive environments in AR and VR applications.
From to and global illumination, these methods enhance visual quality. They capture subtle lighting effects, accurate reflections, and atmospheric depth, bringing virtual worlds to life with unprecedented realism.
Physically-Based Rendering Techniques
Simulating Realistic Materials and Lighting
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- Physically-based rendering () aims to simulate the interaction of light with materials based on real-world physical properties
- PBR uses measured or derived material properties (albedo, roughness, metalness) to accurately represent how light interacts with surfaces
- PBR techniques produce more realistic and consistent results across different lighting conditions compared to traditional ad-hoc shading models
- PBR engines often use a (Bidirectional Reflectance Distribution Function) to model the reflection and scattering of light on a surface
Ray Tracing for Accurate Reflections and Refractions
- Ray tracing is a rendering technique that simulates the path of light rays as they interact with objects in a scene
- Rays are cast from the camera through each pixel and traced as they bounce off surfaces, generating accurate reflections, refractions, and shadows
- Ray tracing can produce highly realistic images with effects like glossy reflections, transparent materials (glass), and complex light interactions
- Real-time ray tracing is becoming more feasible with hardware acceleration (dedicated ray tracing cores) and optimized algorithms
Approximating Reflections and Ambient Occlusion
- () approximate reflections by using the information already rendered on the screen
- SSR traces rays in screen space to find the reflected point, allowing for real-time reflections without the need for expensive ray tracing
- () simulates the shadowing effect caused by objects blocking ambient light
- AO techniques (screen space ambient occlusion, horizon-based ambient occlusion) approximate the occlusion by analyzing the depth buffer or geometry in screen space
- AO adds contact shadows and enhances the visual depth and realism of a scene
Global Illumination Methods
Simulating Indirect Lighting
- Global illumination () simulates the bouncing and scattering of light in a scene, capturing the indirect lighting effects
- GI takes into account the light that reflects off surfaces and illuminates other objects, creating a more realistic and immersive lighting environment
- GI techniques aim to approximate the complex light transport equations to produce convincing indirect lighting in real-time
- Examples of GI methods include , , and
Light Probes and Irradiance Maps
- Light probes are captured snapshots of the lighting environment at specific points in a scene
- Light probes store the incoming light from all directions, allowing objects to receive indirect lighting from the environment
- Irradiance maps are precomputed textures that store the diffuse indirect lighting at different points in a scene
- Objects can sample the irradiance map to receive indirect lighting based on their position, providing a fast approximation of global illumination
- Light probes and irradiance maps are often used together to capture both the high-frequency specular and low-frequency diffuse indirect lighting
Volumetric Lighting Effects
- Volumetric lighting simulates the scattering of light through participating media (fog, dust, smoke)
- Volumetric lighting adds atmospheric depth and enhances the mood and atmosphere of a scene
- Techniques like and (visible light shafts) are used to create realistic volumetric lighting effects
- Volumetric lighting can be achieved through ray marching, where the volume is sampled along the view rays to accumulate the scattered light
- Optimizations like temporal reprojection and low-resolution rendering are often employed to achieve real-time performance for volumetric lighting
Advanced Shadowing Techniques
Shadow Mapping and Filtering
- is a technique used to generate real-time shadows by rendering the scene from the light's perspective
- The depth information from the light's view is stored in a shadow map, which is then used to determine if a pixel is in shadow or not
- Shadow mapping suffers from aliasing artifacts due to the limited resolution of the shadow map
- () is a technique used to soften shadow edges by sampling multiple points around the shadow map and averaging the results
- PCF helps to reduce the jagged appearance of shadow edges and improves the overall quality of shadows
Cascaded Shadow Maps and Variance Shadow Maps
- () divide the view frustum into multiple depth ranges (cascades) and use a separate shadow map for each cascade
- CSMs allow for higher shadow map resolution near the camera and lower resolution for distant objects, optimizing memory usage and quality
- Cascaded shadow maps improve shadow quality and reduce aliasing artifacts, especially for large outdoor scenes
- () store the mean and variance of the depth values in the shadow map instead of just the depth itself
- VSMs enable efficient filtering of shadow maps and can produce soft shadows with a single shadow map
- Variance shadow maps are less prone to aliasing and can handle complex occluders, but may suffer from light bleeding artifacts in some cases
Key Terms to Review (22)
Ambient occlusion: Ambient occlusion is a shading method used in 3D graphics that helps to calculate how exposed each point in a scene is to ambient lighting. It simulates soft shadows that occur in creases, holes, and corners where light has a harder time reaching, adding depth and realism to the rendered objects. This technique plays a crucial role in enhancing the visual quality of environments, making them feel more lifelike and immersive.
Ao: Ambient occlusion (ao) is a shading method used in 3D computer graphics to calculate how exposed each point in a scene is to ambient lighting. It helps to create a sense of depth and realism by simulating the way light behaves in the real world, where certain areas receive less light due to obstruction by other objects. By adding ao to rendering techniques, artists can achieve more natural-looking scenes with soft shadows and enhanced detail.
Cascaded Shadow Maps: Cascaded shadow maps are a rendering technique used to create high-quality shadows in 3D graphics, particularly for scenes with varying depth. This method divides the view frustum into multiple sections or 'cascades', each with its own shadow map, allowing for greater detail in shadows close to the camera while maintaining performance in distant areas. The use of multiple maps enhances shadow quality and reduces artifacts, making it essential for advanced lighting and global illumination techniques.
Csms: CSMS, or Contextualized Spatial Mapping System, refers to a technique used in augmented and virtual reality to create a spatial map that is aware of and responsive to the environment around it. This allows virtual objects to be integrated seamlessly into real-world settings, enhancing the immersive experience for users. The effectiveness of CSMS relies on advanced lighting and global illumination techniques to ensure that these virtual elements interact naturally with real-world lighting conditions and shadows.
Gi: Global illumination (gi) refers to a set of advanced lighting techniques used in computer graphics to simulate how light interacts with surfaces and materials in a scene, providing a more realistic representation of light behavior. It encompasses both direct lighting, which comes from light sources, and indirect lighting, which results from light bouncing off surfaces, illuminating other areas in a way that mimics real-world physics. By incorporating gi, artists and engineers can create scenes that appear more lifelike through improved color bleeding, soft shadows, and overall depth.
Global Illumination: Global illumination refers to a group of techniques used in 3D computer graphics to simulate how light interacts with surfaces, accounting for both direct and indirect lighting effects. This approach enhances realism in rendered images by considering how light bounces off surfaces and illuminates other areas, resulting in more accurate shading and color representation. Global illumination is crucial for achieving lifelike visuals, especially in complex environments where light behavior is intricate.
God rays: God rays, also known as light shafts or crepuscular rays, refer to the visible beams of light that appear to radiate from a single light source, often seen streaming through gaps in clouds or between objects. This phenomenon can enhance the realism and atmosphere in digital environments, making it a key feature in advanced lighting and global illumination techniques where natural light behavior is simulated to create immersive experiences.
Irradiance Maps: Irradiance maps are graphical representations that show the distribution of light energy across a surface in a virtual environment. These maps help simulate how light interacts with surfaces, allowing for more realistic rendering in computer graphics by capturing both direct and indirect lighting effects. They are essential for advanced lighting techniques and play a crucial role in global illumination, enabling artists and engineers to create visually accurate and immersive experiences.
Light Probes: Light probes are specialized tools used in computer graphics and rendering to capture and represent the lighting information in a 3D environment. They allow for accurate simulation of how light interacts with surfaces, contributing to realistic global illumination by sampling light data from various angles and positions. This technique enhances the visual quality of scenes, enabling dynamic lighting and reflections that adapt to changes in the environment.
Microfacet-based brdf: Microfacet-based BRDF (Bidirectional Reflectance Distribution Function) is a mathematical model used in computer graphics to describe how light interacts with surfaces at a micro-scale level. This model assumes that surfaces are made up of many tiny, flat facets, each reflecting light according to its orientation, allowing for more realistic rendering of materials like metals and plastics. By incorporating the microgeometry of a surface, this approach helps simulate complex lighting interactions, enhancing the overall realism in rendering scenes.
PBR: PBR, or Physically Based Rendering, is a rendering approach that aims to simulate the way light interacts with surfaces in the real world to create more realistic images. This technique relies on physical properties of materials and lighting to produce images that accurately represent how objects appear under various lighting conditions. By utilizing PBR, artists and developers can achieve consistency and realism in their visualizations across different environments and platforms.
PCF: PCF, or Point Cloud Filtering, refers to the process of refining and optimizing point clouds obtained from 3D scanning technologies. This technique is crucial in managing the complexity and quality of point cloud data, as it removes noise and irrelevant points while preserving essential features. Effective PCF is vital for improving the accuracy and visual quality of 3D models in augmented and virtual reality applications.
Percentage-closer filtering: Percentage-closer filtering is a technique used in computer graphics to improve the quality of shadow mapping by blending the results of multiple depth comparisons. It enhances the smoothness of shadows by calculating the percentage of light that reaches a point based on its distance from shadow casters, which reduces artifacts and creates softer shadow edges. This method is particularly important in advanced lighting and global illumination techniques, as it contributes to more realistic scene representation.
Physically-Based Rendering: Physically-based rendering (PBR) is a rendering technique that aims to simulate the interaction of light with surfaces in a way that closely mimics real-world physics. This approach ensures that materials respond accurately to lighting conditions, which enhances realism in computer graphics, especially in complex lighting environments. By using properties like albedo, roughness, and metallicity, PBR allows for more consistent results across different lighting scenarios, making it essential for advanced lighting techniques and global illumination.
Ray Tracing: Ray tracing is a rendering technique used to simulate the way light interacts with objects to produce realistic images by tracing rays of light as they travel through a scene. This method allows for detailed reflections, refractions, and shadows, making it a critical component in achieving high-quality visual effects in computer graphics. Its connection to advanced rendering techniques enhances lighting accuracy and contributes to the overall realism of virtual environments.
Screen Space Reflections: Screen space reflections (SSR) is a rendering technique used in computer graphics to create realistic reflections by utilizing information from the current frame rendered on the screen. This method enhances visual fidelity by reflecting the environment and other objects dynamically, which helps in achieving a more immersive experience in virtual environments. SSR is particularly relevant in advanced lighting and global illumination techniques, as it contributes to more believable interactions between light and surfaces.
Shadow mapping: Shadow mapping is a computer graphics technique used to create shadows in a scene by determining the areas that are blocked from a light source. This method involves rendering the scene from the perspective of the light source to create a depth map, which is then used to calculate shadows during the final rendering pass. It enhances the realism of lighting effects, making it a crucial aspect of various lighting models and advanced global illumination techniques.
SSR: SSR, or Screen Space Reflections, is a rendering technique used in computer graphics that simulates reflective surfaces by utilizing information from the screen space. This method enhances the realism of scenes by providing dynamic reflections based on the visible geometry and textures within the frame, thus contributing to advanced lighting and global illumination techniques.
Variance Shadow Maps: Variance Shadow Maps (VSM) are a technique used in computer graphics to improve the quality of shadow rendering by storing variance information in addition to depth values. This method allows for smoother, more realistic shadows and helps to reduce artifacts commonly associated with shadow mapping techniques. By utilizing statistical data, VSM can handle soft shadows, which are important for creating a more believable lighting environment.
Volumetric Fog: Volumetric fog is a rendering technique used in computer graphics to simulate the appearance of fog and other atmospheric effects, enhancing depth and realism in a scene. This technique allows light to interact with particles suspended in the air, creating soft shadows and diffused light that contribute to the overall mood and atmosphere. By accurately modeling how light scatters through fog, it provides a more immersive experience in virtual environments.
Volumetric Lighting: Volumetric lighting refers to the technique of simulating light interacting with particles in the air, creating beams or shafts of light that enhance the visual depth and atmosphere of a scene. This technique is crucial for adding realism, as it allows light to scatter and create effects like fog or mist, highlighting the presence of volumetric elements. By incorporating volumetric lighting, artists can convey a sense of space and dimension, ultimately enriching the viewer's experience.
VSMS: VSMS, or Virtual Scene Management System, is a framework designed to optimize the rendering of complex virtual environments by efficiently managing scene data. This system helps in organizing and culling 3D objects, ensuring that only relevant elements are processed and rendered at any given time, which is crucial for achieving high-performance graphics in augmented and virtual reality applications.