This post proposes a taxonomy for classifying rendering engines based on two key dimensions: the scene representation (explicit vs. implicit) and the rendering technique (rasterization vs. ray tracing). Explicit representations, like triangle meshes, directly define the scene geometry, while implicit representations, like signed distance fields, define the scene mathematically. Rasterization projects scene primitives onto the screen, while ray tracing simulates light paths to determine pixel colors. The taxonomy creates four categories: explicit/rasterization (traditional real-time graphics), explicit/ray tracing (becoming increasingly common), implicit/rasterization (used for specific effects and visualizations), and implicit/ray tracing (offering unique capabilities but computationally expensive). The author argues this framework provides a clearer understanding of rendering engine design choices and future development trends.
The blog post "A Taxonomy for Rendering Engines" proposes a classification system for organizing the diverse landscape of 3D rendering engines. It argues that traditional categorizations, such as "rasterization" vs. "ray tracing," are insufficient to capture the nuanced differences between modern rendering approaches, especially with the emergence of hybrid techniques. The author introduces a two-dimensional taxonomy based on two key aspects of a rendering engine: its primitive representation and its shading algorithm.
The primitive representation axis describes how the scene's geometry is represented for rendering purposes. The author identifies three primary categories: surface, volume, and point. Surface representations, the most common type, define objects using surfaces like triangles and meshes. Volume representations, often used for effects like smoke and fire, represent objects as density fields within a 3D volume. Point representations define objects as collections of points, often derived from point clouds or other sampled data.
The shading algorithm axis describes how the appearance of each primitive is determined. The author identifies four primary categories: rasterization, ray tracing, point tracing, and splatting. Rasterization projects primitives onto the screen and calculates shading for each pixel covered by the projected primitive. Ray tracing casts rays from the camera into the scene, calculating shading based on the intersections of these rays with scene geometry. Point tracing is similar to ray tracing but operates on point primitives, casting rays from the camera to illuminate individual points. Splatting projects each primitive onto the screen and applies a pre-computed "splat" or kernel function to distribute its contribution across neighboring pixels.
The author emphasizes that this taxonomy isn't meant to be rigid or exhaustive. Some rendering engines may utilize multiple primitive representations or shading algorithms, placing them in multiple categories within the taxonomy. Furthermore, the taxonomy doesn't account for every detail of a rendering engine's architecture, such as acceleration structures or specific shading models. However, the author argues that this classification scheme provides a valuable framework for understanding the core functionalities of different rendering engines and comparing their strengths and weaknesses. The author concludes by positioning various existing rendering engines within this taxonomy, illustrating its practical application. For instance, a typical game engine using triangle meshes and rasterization would fall into the "surface/rasterization" category, while a renderer for scientific visualization using point clouds and splatting would be classified as "point/splatting". The post suggests that this taxonomy can help developers choose the right rendering engine for a specific task and inspire the development of new hybrid rendering approaches.
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https://news.ycombinator.com/item?id=43908220
Hacker News users discuss the proposed taxonomy for rendering engines, mostly agreeing that it's a useful starting point but needs further refinement. Several commenters point out the difficulty of cleanly categorizing existing engines due to their hybrid approaches and evolving architectures. Specific suggestions include clarifying the distinction between "tiled" and "immediate" rendering, addressing the role of compute shaders, and incorporating newer deferred rendering techniques. The author of the taxonomy participates in the discussion, acknowledging the feedback and indicating a willingness to revise and expand upon the initial classification. One compelling comment highlights the need to consider the entire rendering pipeline, rather than just individual stages, to accurately classify an engine. Another insightful comment points out that focusing on data structures, like the use of a G-Buffer, might be more informative than abstracting to rendering paradigms.
The Hacker News post "A Taxonomy for Rendering Engines" sparked a modest discussion with a handful of comments, primarily focusing on clarifying terms and offering alternative perspectives on categorizing rendering engines.
One commenter pointed out the frequent misuse of the term "rasterization" within the 3D graphics community. They argue that the term should specifically refer to the process of converting primitives into fragments, not the broader pipeline that includes fragment shading and other operations. They suggest "scan conversion" as a more appropriate term for the full process of creating a 2D image from 3D geometry. This comment sparked a brief exchange where another user agreed with the distinction, highlighting how the term "rasterization" can conflate different stages of the rendering pipeline.
Another commenter questioned the placement of signed distance field rendering within the taxonomy. They suggested it's more of an acceleration structure rather than a fundamental rendering technique, comparing it to techniques like bounding volume hierarchies. This comment prompted the author of the original article to respond and clarify their reasoning. They explained that signed distance fields can be considered a rendering technique due to its ability to represent geometry implicitly and because the rendering process inherently involves sampling and evaluating the distance field. They acknowledge that SDFs can also be used as acceleration structures but emphasize their distinct use as a rendering technique in certain contexts.
Furthermore, there was a discussion around ray tracing versus path tracing, with one commenter seeking clarification on their relationship. The author of the article explained that path tracing is a specific type of ray tracing algorithm that simulates global illumination by recursively tracing light paths. They also clarified that ray tracing isn't solely for photorealistic rendering, highlighting its use in non-photorealistic rendering techniques as well.
A different commenter proposed an alternative way of categorizing rendering engines based on their shading model, specifically highlighting physically-based rendering and the distinction between local and global illumination models. This suggests a different axis for classifying renderers beyond the core techniques discussed in the original article.
Finally, a commenter touched on the complexity of classifying modern rendering engines, noting that many combine multiple techniques, such as using rasterization for primary visibility and ray tracing for select effects. This comment underlines the limitations of strict categorization and the evolving nature of rendering technologies.