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Peer-to-Peer Ordered Search Indexes
Dec 19, 2020 · original
“Can we do to web services what Linux did to the operating systems?” Imagine what the web with a P2P GitHub, a P2P YouTube, a P2P Twitter, a P2P Google search, and so on. But getting started with P2P services remains difficult, because: “There is no P2P PostGRES!” This is a very hard problem, so instead consider a more modest project: “Let’s build a dynamic P2P ordered search index” While pretty far from a full SQL database, a search index is a critical component for a modern RDBMS as it enables the following sorts of queries: Predecessor/successor Range search ORDER-BY Multi column joins …and much more In this post we’ll talk about a few standard solutions to this problem, explain why they don’t work so well in P2P systems and finally we’ll present an idea that both simplifies these data structures and solves these problems. Quick review: Merkle DAGs For the uninitiated, building robust
Geometry without geometric algebra
Nov 4, 2018 · original
When I was younger I invested a lot of time into studying geometric algebra . Geometric algebra is a system where you can add, subtract and multiply oriented linear subspaces like lines and hyperplanes (cf. Grassmanian ). These things are pretty important if you’re doing geometry, so it’s worth it to learn many ways to work with them. Geometric algebra emphasizes exterior products as a way to parameterize these primitives (cf. Plücker coordinates ). Proponents claim that it’s simpler and more efficient than using “linear algebra”, but is this really the case? In this blog post I want to dig into the much maligned linear algebra approach to geometry. Specifically we’ll see: Two ways to parameterize a linear subspace using matrices How to transform subspaces How to compute the intersection and span of any two subspaces Encoding flats A subspace of a vector space is a subset of vectors whic
A level of detail method for blocky voxels
Mar 3, 2018 · original
Large voxel terrains may contain millions of polygons. Rendering such terrains at a uniform scale is both inefficient and can lead to aliasing of distant objects. As a result, many game engines choose to implement some form of level of detail based rendering, so that distant terrain is rendered with less geometry. In this post, I’ll talk about a simple technique based on vertex clustering with some optimizations to improve seam handling. The specific ideas in this article are applied to Minecraft-like blocky terrain using the same clustering/sorting scheme as POP buffers. M. Limper, Y. Jung, J. Behr, M. Alexa: “ The POP Buffer: Rapid Progressive Clustering by Geometry Quantization “, Computer Graphics Forum (Proceedings of Pacific Graphics 2013) Review of POP buffers Progressively Ordered Primitive (POP) buffers are a special case of vertex clustering, where for each level of detail we r
Voxel lighting
Feb 21, 2018 · original
Been a long time since I’ve written anything here. Lately I’ve been working on a new multiplayer WebGL voxel engine for codemao (an educational platform to teach kids programming via games). It’s not live yet, but a bunch of neat ideas have come out of this project. In this post I want to talk about the lighting model and share some of the tricks which were used to speed up processing. Conceptually the basic lighting system is similar to the one used in Minecraft and Seed of Andromeda with a few small tweaks. For background information, I would recommend the following sources: Ambient occlusion for Minecraft-like worlds Lighting – Minecraft Wiki Fast flood fill lighting in a voxel game – Part 1 (dead link) Fast flood fill lighting in a voxel game – Part 2 (dead link) This post describes some extensions and optimizations to the basic flood fill lighting model proposed by Ben Arnold. In pa
Collision detection (part 3): Benchmarks
Jan 23, 2015 · original
Previously in this series we covered the basics of collision detection and discussed some different approaches to finding intersections in sets of boxes: Collision detection (part 1): Overview Collision detection (part 2): Box intersection Today, we’ll see how well this theory squares with reality and put as many algorithms as we can find to the test. For those who want to follow along with some code, here is a link to the accompanying GitHub repo for this article: The Great JavaScript Box Intersection Benchmark Finding modules To get a survey of the different ways people solve this problem in practice, I searched GitHub, Google and npm, and also took several polls via IRC and twitter. I hope that I managed to cover most of the popular libraries, but if there is anything here that I missed, please leave a comment and let me know. While it is not an objective measurement, I have also trie
Collision detection (part 2): Box intersection
Jan 18, 2015 · original
Last time , we discussed collision detection in general and surveyed some techniques for narrow phase collision detection. In this article we will go into more detail on broad phase collision detection for closed axis-aligned boxes . This was a big problem in the 1970’s and early 1980’s in VLSI design , which resulted in many efficient algorithms and data structures being developed around that period. Here we survey some approaches to this problem and review a few theoretical results. Boxes A box is a cartesian product of intervals , so if we want to represent a d-dimensional box, it is enough to represent a tuple of d 1-dimensional intervals. There are at least two ways to do this: As a point with a length As a pair of upper and lower bounds For example, in 2D the first form is equivalent to representing a box as a corner point together with its width and height (e.g. left, top, width,
Collision detection (part 1): Overview
Jan 7, 2015 · original
Collision, or intersection, detection is an important geometric operation with a large number of applications in graphics, CAD and virtual reality including: map overlay operations , constructive solid geometry , physics simulation , and label placement . It is common to make a distinction between two types of collision detection: Narrow phase : Test if 2 objects intersect Broad phase : Find all pairs of intersections in a set of n objects In this series, I want to focus on the latter (broad phase), though first I want to spend a bit of time surveying the bigger picture and explaining the significance of the problem and some various approaches. Narrow phase The approach to narrow phase collision detection that one adopts depends on the types of shapes involved: Constant complexity shapes While it is true that for simple shapes (like triangles, boxes or spheres) pairwise intersection dete
Replication in network games: Bandwidth (Part 4)
Mar 9, 2014 · original
Last time , I finished up talking about latency issues for networked video games. Today I want to move onto the other major network resource, which is bandwidth . Compared to latency, bandwidth is much easier to discuss. This has been observed many times, perhaps most colorfully by Stuart Cheshire: S. Cheshire. (1996) “ It’s the latency stupid! “ Though that article is pretty old, many of its points still ring true today. To paraphrase a bit, bandwidth is not as big a deal as latency because: Analyzing bandwidth requirements is easy, while latency requirements are closely related to human perception and the nature of the game itself. Bandwidth scales cheaply, while physical constraints impose limitations on latency. Optimizing for low bandwidth usage is a purely technical problem, while managing high latency requires application specific design tradeoffs. Costs of bandwidth But while it
Replication in networked games: Space/time consistency (Part 3)
Feb 26, 2014 · original
Last time in this series, I talked about latency and consistency models. I wanted to say more about the last of these, local perception filtering , but ended up running way past the word count I was shooting for. So I decided to split the post and turn that discussion into today’s topic. Causality Sharkey and Ryan justified local perception filters based on the limitations of human perception. In this post I will take a more physical approach derived from the causal theory of special relativity . For the sake of simplicity, we will restrict ourselves to games which meet the following criteria: The game exists within a flat space-time . All objects in the game are point-particles . All interactions are local . There is an upper bound on the speed of objects . Many games meet these requirements. For example, in Realm of the Mad God , gameplay takes place in a flat 2D space. Objects like pl
Replication in networked games: Latency (Part 2)
Feb 17, 2014 · original
The last post in this series surveyed replication in network games at a high level. In this article and the next, I want to go deeper into the issues surrounding replication. One of the most annoying aspects of online gaming is latency . Latency , or lag, is the amount of time between when a user pushes a button and when the state of the game updates. To quantify the effects of lag, we refer to the following experiment by Pantel and Wolf: L. Pantel, L. Wolf. (2002) “ On the impact of delay in real-time multiplayer games ” NOSSDAV 2002 In that experiment, they measured the performance of players in a racing game with varying input delays. Amongst other things they conclude that, Latency is negatively correlated with performance and subjective immersion Input latency above 500ms is not acceptable Below 50ms the effects of latency are imperceptible And these conclusions are validated by oth

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