Area chart

AreaChart (insightdock/area_chart.h) draws filled polygons from series values down to the baseline, with an optional stacked mode — the tool for cumulative/composition-over-category views that LineChart's single-series fill_area isn't meant to cover.

Minimal example

#include "insightdock/charts.h"

using namespace insightdock::charts;

AreaChart area;
area.set_categories({"Mon", "Tue", "Wed", "Thu", "Fri"});
area.add_series("Download", {120, 180, 150, 220, 190});
area.add_series("Upload", {40, 55, 48, 70, 62});
area.area_options().stacked = true;
ChartExporter::save(area, "area.png");

AreaChartOptions

Accessed via area.area_options():

Option	Default	Purpose
stacked	false	Stack series polygons instead of overlapping them.
stacked_percent	false	100%-stacked: every category is normalised to 100% and the axis runs 0–100%. Implies stacking; negative/missing values count as 0.
step	StepMode::None	Staircase edges (After, Before, Middle) instead of straight segments; takes precedence over spline.
show_line	true	Draw a stroke on top of each filled area.
line_width	2.0	Stroke width in pixels, when show_line is true.
spline	false	Catmull-Rom cubic interpolation for both the fill and the stroke edge.
dash	empty (solid)	Alternating on/off stroke lengths in pixels for the top edge. Chart-wide default; override per series with SeriesStyle (see Line → Per-series style).
gap_policy	GapPolicy::Gap	How NaN/Inf/missing values are drawn in non-stacked areas. In stacked mode a missing value counts as 0.
show_points	false	Point markers along the top edge — off by default, unlike LineChart.
point_radius	4.0	Marker radius when show_points is true.
point_shape	PointMarkerShape::Circle	Circle, Square, Triangle, or Cross.
data_labels	disabled	DataLabelOptions — draws each point's formatted value above the top edge.

With stacked = false (the default), each series' polygon is drawn independently down to the baseline and series will visually overlap where their fills' alpha lets the one below show through — appropriate for comparing a small number of overlapping trends. With stacked = true, each series is drawn on top of the running total of the ones before it, so the top edge of the topmost polygon represents the sum across all series at each category — appropriate for part-to-whole-over-time views (bandwidth by protocol, revenue by product line, etc.).

Shared axis options

AreaChart is a CartesianChart subclass, so cartesian_options() (tick format, axis labels, label density) works exactly as documented in Bar → Shared CartesianOptions, and reference_lines/reference_bands work as documented in Bar → Reference lines and bands.

Like LineChart, AreaChart also supports a logarithmic y-axis (Bar → Log y-axis) and a continuous DateTime x-axis positioned by real timestamp via set_x_values() (Bar → Continuous DateTime x-axis).