Model: Series.trendlines (Vec<Trendline>, serde default) with kind
(linear, exponential, logarithmic, polynomial 2..6, power, moving
average 2..255), name, forward/backward forecast, set intercept,
equation / R² display and line colour, width and dash.
XLSX: read and write <c:trendline> in CT_Trendline child order, placed
after dLbls and before the data references in line, bar, area, scatter,
bubble and stock series; unknown types are skipped.
Chart: least-squares fits (transformed for exp/log/power, skipping
non-positive values; polynomials via normal equations on centred,
scaled x with partial pivoting), moving averages, forecasts that widen
the category or x axis, clipping to the plot, equation and R² labels and
legend entries ("Linear (Sales)"). Degenerate data draws nothing.
Engine: chart.addElement element="trendline" adds (type, series, order,
period, forward, backward, displayEquation, displayRSquared) or removes
trendlines; document.inspect lists each chart's trendlines.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A chart linked to a PivotTable: series are built from the report
(innermost row items x column items/value fields, totals excluded) and
rebuilt on every refresh or layout change; c:pivotSource round trip;
chart series accept union references.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A combo chart whose series have no kind of their own (as insert.chart
makes them) was written as one column group, and a stock chart as
clustered columns, so both reopened as clustered columns. Combo series
are now written as drawn (the first as columns, the others as lines),
and stock charts as a stockChart group (as lines when they don't have
the 3 or 4 series a stock chart needs).
Add support for Excel's "smoothed line" chart style. The smooth flag flows
model -> resolve -> chart render, persists through XLSX (<c:smooth val="1"/>),
and is toggled via the chart.addElement "smooth" element.
Rendering interpolates each gap-free run with a uniform Catmull-Rom spline
(0.5 tangent scale, 100 sub-segments per data segment), so the curve passes
through every data point and rounds the vertices — matching Excel's observed
behaviour. Long runs are still decimated before smoothing.
- model: Series.smooth (#[serde(default)], so old workbooks load unchanged)
- chart: SeriesData.smooth; smooth_run + catmull in render; wired through
resolve and the sanitize() copy; draw_runs takes the flag (line + scatter)
- engine: chart.addElement element="smooth"
- xlsx: read/write <c:smooth val> instead of hard-coding val="0"
- tests: smooth_line_adds_interpolated_points_and_keeps_endpoints,
smooth_line_splits_at_gaps, smooth_line_setting_round_trips
- examples/smooth_demo.rs: generates a straight+smooth side-by-side workbook
cargo xtask ci: all 7 steps pass.
