Until now a startbox was a rectangle, and any map whose starting area wasn't designed to be rectangular had to settle for a startbox that was merely an approximation of what was desired - boxes that spilled into water, over cliffs, or across a chokepoint they were never meant to include. Maps can now define a startbox as a polygon of three or more points, with optional per-vertex curvature so an area can follow a coastline or a ridge rather than step around it.

The shape is real, not decorative. The game reads the polygon and uses it for the normal pre-game choose-your-start experience, so where you're allowed to place your commander matches what you saw in lobby, on the minimap. The lobby draws the same curves the game does, using the same spline math, so the two can't drift apart. Custom startbox configurations travel as the mapmetadata_startbox_override modoption only; one !bSet per edit (one vote), no !loadboxes/!addbox/!split/!clearbox. This opens up possibilities for improved UX in the future for non-boss'd rooms that want to modify the startboxes without incurring a dozen separate votes.

Map makers define boxes in Rowy; existing rectangle startboxes specified there keep working but can be changed at any time to use polygons if desired. The implementation in Rowy has similarly been updated to provide a UX that allows for polygon startboxes, and if you want to build a set by hand (such as to create an override), there's a standalone editor at https://bar-custom-startboxes.pages.dev/ that produces the encoded value directly and provides a convenient way to paste it in in-lobby by using a modoption to control the override. The polygon implementation uses catmull-rom splines with in-game using Note: the length of the override is capped at 1Kb.

The previous commands used to set startboxes (!loadboxes, !split, !addbox, etc.) are no longer the intended drivers for controlling startboxes in-game. Tool-makers are encouraged to reference the updated implementation in game, chobby, or the standalone startbox creator and update their tools to match the output used now. Notably:

!bSet mapmetadata_startbox_override < base64 encode of zlib.deflate of polygon startbox json data >