#Metrics Internals

#Live Metrics

Live metrics are computed in the WebGPU worker. They are planned by section and device-safe counter limits, then encoded as compute passes against the current packed grid.

Population and diversity depend on the histogram pass:

• The histogram shader uses $256$ atomic counters in workgroup memory and global storage.
• Counts are by numeric tribe index.
• Alive cells are total cells minus the dead tribe count.
• Occupancy is alive cells divided by total cells.
• Shannon entropy and Simpson index are computed from alive tribe probabilities.

Interfaces use a boundary pass:

• Each cell checks only right and bottom neighbors.
• Toroidal grids wrap those checks and have $\texttt{cols}\cdot\texttt{rows}\cdot2$ total contact edges.
• Bounded grids skip checks beyond the right and bottom edges and have $\texttt{rows}\cdot(\texttt{cols}-1)+\texttt{cols}\cdot(\texttt{rows}-1)$ total contact edges.
• Cross-state edges are counted directly.
• Same-state edges are total contact edges minus cross-state edges.

#Offline Metrics

Download metrics scan recorded frames in the download worker. They decode packed rows, update population histograms, count frontier/contact edges using the recorded grid topology, and compare with the previous frame when generations are consecutive. Toroidal exports wrap edge contacts; bounded exports count only contacts between stored cells and do not include virtual boundary cells.

Offline transition metrics include:

• Changed cells.
• Births.
• Deaths.
• Tribe switches.

#Limits

Live metrics rely on $32$-bit unsigned GPU counters:

• Population and diversity are available when $\texttt{cols}\cdot\texttt{rows}\leq\texttt{0xffffffff}$.
• Interfaces are available when $\texttt{cols}\cdot\texttt{rows}\cdot2\leq\texttt{0xffffffff}$.

If a section is enabled but not safe for counters, the UI marks it unavailable. If disabled globally or per section, it is marked disabled.

Download metric estimates use these constants:

• Metric entry base: $512\text{ bytes}$.
• Metric entry per tribe: $160\text{ bytes}$.
• Metrics CSV row base: $384\text{ bytes}$.
• Metrics CSV row per tribe: $48\text{ bytes}$.
• Streaming metric-entry threshold: $512\text{ MiB}$.
• Large metrics CSV warning threshold: $512\text{ MiB}$.