# Charting architecture

## Decision: one chart engine for all live metrics

**Engine:** `github.com/go-analyze/charts` (pure Go, no CGO, SVG output)
**Theme:** `grafana` (dark background, coloured lines)

All live metrics charts in the web UI are server-side SVG images served by Go
and polled by the browser every 2 seconds via `<img src="...?t=now">`.
There is no client-side canvas or JS chart library.

## Rule: live charts must be visually uniform

Live charts are a single UI family, not a set of one-off widgets. New charts and
changes to existing charts must keep the same rendering model and presentation
rules unless there is an explicit architectural decision to diverge.

Default expectations:

- same server-side SVG pipeline for all live metrics charts
- same refresh behaviour and failure handling in the browser
- same canvas size class and card layout
- same legend placement policy across charts
- same axis, title, and summary conventions
- no chart-specific visual exceptions added as a quick fix

Current default for live charts:

- legend below the plot area when a chart has 8 series or fewer
- legend hidden when a chart has more than 8 series
- 10 equal Y-axis steps across the chart height
- 1400 x 360 SVG canvas with legend
- 1400 x 288 SVG canvas without legend
- full-width card rendering in a single-column stack

If one chart needs a different layout or legend behaviour, treat that as a
design-level decision affecting the whole chart family, not as a local tweak to
just one endpoint.

### Why go-analyze/charts

- Pure Go, no CGO — builds cleanly inside the live-build container
- SVG output — crisp at any display resolution, full-width without pixelation
- Grafana theme matches the dark web UI colour scheme
- Active fork of the archived wcharczuk/go-chart

### SAT stress-test charts

The `drawGPUChartSVG` function in `platform/gpu_metrics.go` is a separate
self-contained SVG renderer used **only** for completed SAT run reports
(HTML export, burn-in summaries). It is not used for live metrics.

### Live metrics chart endpoints

| Path | Content |
|------|---------|
| `GET /api/metrics/chart/server.svg` | CPU temp, CPU load %, mem load %, power W, fan RPMs |
| `GET /api/metrics/chart/gpu/{idx}.svg` | GPU temp °C, load %, mem %, power W |

Charts are 1400 × 360 px SVG when the legend is shown, and 1400 × 288 px when
the legend is hidden. The page renders them at `width: 100%` in a
single-column layout so they always fill the viewport width.

### Ring buffers

Each metric is stored in a 120-sample ring buffer (2 minutes of history at 1 Hz).
Buffers are per-server or per-GPU and grow dynamically as new GPUs appear.
