Scatter & bubble chart

ScatterChart (insightdock/scatter_chart.h) plots continuous numeric x/y points — unlike every other chart type in the library, its x-axis is not a category list, so points need not be evenly spaced or sorted. Setting a point's radius turns it into a bubble marker, sized relative to the other bubble points in the chart.

Scatter	Bubble

Minimal example (plain scatter)

#include "insightdock/charts.h"

using namespace insightdock::charts;

ScatterChart chart;
chart.scatter_options().x_axis_label = "Throughput (Mbps)";
chart.scatter_options().y_axis_label = "Latency (ms)";
chart.add_series("Device A", {{12, 40}, {25, 35}, {40, 28}, {55, 30}, {70, 18}, {90, 15}});
ChartExporter::save(chart, "scatter.png");

{x, y} braces construct a ScatterPoint{x, y, radius} with radius defaulting to 0 — a plain, uniformly-sized marker.

Bubble variant

Set a positive third value (radius) on any point to enable bubble sizing for it — the marker scales between min_bubble_radius and max_bubble_radius based on that value relative to other bubble points in the chart. Points left at radius 0 always draw at the fixed ScatterOptions::point_radius:

ScatterChart bubble;
bubble.scatter_options().x_axis_label = "Avg session (min)";
bubble.scatter_options().y_axis_label = "Bounce rate (%)";
bubble.add_series("Sites", {
    {3.2, 42, 120},  // {x, y, radius} — radius drives bubble size
    {5.1, 35, 480},
    {2.0, 58, 90},
    {7.4, 22, 950},
});
ChartExporter::save(bubble, "bubble.png");

ScatterOptions

Accessed via chart.scatter_options():

Option	Default	Purpose
x_axis_label	empty	Label below the x-axis.
y_axis_label	empty	Label beside the y-axis.
begin_at_zero_x	false	Force the x-axis minimum to 0.
begin_at_zero_y	false	Force the y-axis minimum to 0.
point_radius	5.0	Marker radius (pixels) for points with radius == 0.
min_bubble_radius	4.0	Smallest rendered bubble radius, pixels.
max_bubble_radius	40.0	Largest rendered bubble radius, pixels.
fill_opacity	0.65	Marker fill alpha, 0–1.
point_shape	PointMarkerShape::Circle	Circle, Square, Triangle, or Cross. Applies to every point — no per-point override.
data_labels	disabled	DataLabelOptions — labels each point with its formatted Y value (no per-point custom label in v1).

ScatterChart has no draw_overlay() hook, so it doesn't support ReferenceLine/ReferenceBand — those are CartesianChart-only (see Bar → Reference lines and bands).

Why not CartesianChart?

ScatterChart derives directly from Chart, not CartesianChart — both axes are continuous numeric Scales over the data domain rather than a fixed category list, so the category-axis machinery CartesianChart provides (and that BarChart/LineChart/AreaChart/ComboChart share) doesn't apply here. See Concepts → Class hierarchy for the full reasoning if you're deciding which base to use for a new chart type.