July 12, 2026
Circles, chaos, and one crowned king
Circular Obstacle Pathfinding (2017)
The internet crowns this obstacle-dodging explainer a total gem
TLDR: The article shows how a computer can find the best route around round obstacles by mixing straight moves with curves around the edges. The community reaction was overwhelmingly adoring, with readers treating Red Blob Games less like a blog and more like a beloved internet institution.
A 2017 post about finding a way through a forest of round obstacles somehow turned into a mini love letter from the community. The core idea is simple enough for non-math people: instead of moving on little squares like a video game map, the path can slide in straight lines and curve around circles, with the system testing promising routes until it finds the best one. In other words, it’s about teaching a computer to weave through a crowded space without bumping into anything.
But let’s be honest: the loudest reaction wasn’t "wow, neat circles." It was straight-up admiration. The standout comment, from hexasquid, basically summed up the mood in five words: "red blob games is a treasure". And that vibe says everything. There wasn’t much of a bloodbath in the replies here; instead, the drama was the ultra-rare kind for the internet: people being almost suspiciously wholesome about a technical explainer. Imagine opening the comments expecting a nerd cage match and finding a fan club instead.
There’s also a little comedy baked into the article itself. The post turns route segments into cute labels like "surfing" between obstacles and "hugging" around them, which feels like geometry got a Pixar rewrite. That playful tone seems to be exactly why readers were so charmed. In a world where many explainers make people feel dumb, this one made at least one commenter want to hand out a crown. Honestly? Fair.
Key Points
- •The article explains that A* pathfinding is not limited to grids and can operate on any graph, including one built from circular obstacles.
- •A* evaluates partial paths using a priority queue ordered by actual path length plus a heuristic underestimate of remaining distance.
- •For circular obstacles, valid paths are modeled as alternating straight segments and obstacle-following arcs, represented as graph edges.
- •The article names straight segments between obstacles as surfing edges and boundary-following arcs as hugging edges.
- •It introduces a tangent visibility graph, where surfing edges are generated from bitangents between pairs of circles, including internal and external bitangents.