LineChart: Continuous Trends, Markers & Splines

The LineChart component (drawlib.charts.line) visualizes numerical trends over ordered categories or time intervals. It supports straight polygonal segments (smooth=False), smoothed spline curves (smooth=True), per-series vertex marker shapes ("circle", "square", "none"), configurable stroke patterns ("solid", "dashed", "dotted", "dashdot"), inline vertex value labels, and decoupled legend rendering.

1. Overview & Key Modes

line_1
LineChart Modes: Smooth Cubic Spline Interpolation (smooth=True) vs. Straight Polygonal Segments (smooth=False)
Source Code 
from drawlib.canvas import save, setup
from drawlib.charts.line import LineChart
from drawlib.styles import Styles

setup(width=132, height=52)

categories = ["M1", "M2", "M3", "M4", "M5"]
active_vals = [28.0, 64.0, 42.0, 86.0, 68.0]
baseline_vals = [35.0, 40.0, 45.0, 50.0, 55.0]

# Left: Smooth Spline Curve (smooth=True)
smooth_chart = LineChart(
    axis_line_style=Styles.MutedDashed,
    categories=categories,
    axis_text_style=Styles.Muted.patch(text_size=10.0),
    grid_style=Styles.MutedThin,
    width=56.0,
    height=36.0,
    smooth=True,
    show_points=True,
    point_size=0.65,
    title="1. Smooth Spline Curve (smooth=True)",
    title_style=Styles.BlackBold.patch(text_size=11.0),
)
smooth_chart.add_series("Active", active_vals, style=Styles.PrimaryFlat, line_width=2.2)
smooth_chart.add_series("Baseline", baseline_vals, style=Styles.SecondaryNeutral, line_style="dashed", point_shape="none")
smooth_chart.configure_y_axis(min_value=0.0, max_value=100.0, tick_step=25.0)
smooth_chart.draw(xy=(5.0, 6.0))
smooth_chart.draw_legend(xy=(14.0, 45.0), text_style=Styles.DarkBold.patch(text_size=10.0), orientation="horizontal")

# Right: Straight Segments & Value Labels (smooth=False)
straight_chart = LineChart(
    axis_line_style=Styles.MutedDashed,
    categories=categories,
    axis_text_style=Styles.Muted.patch(text_size=10.0),
    grid_style=Styles.MutedThin,
    value_text_style=Styles.DarkBold.patch(text_size=10.0),
    width=56.0,
    height=36.0,
    smooth=False,
    show_points=True,
    point_shape="square",
    point_size=0.65,
    title="2. Straight Segments & Labels (smooth=False)",
    title_style=Styles.BlackBold.patch(text_size=11.0),
)
straight_chart.add_series("Active", active_vals, style=Styles.PrimaryFlat, line_width=2.2)
straight_chart.add_series("Baseline", baseline_vals, style=Styles.SecondaryNeutral, line_style="dashed", point_shape="none")
straight_chart.configure_y_axis(min_value=0.0, max_value=100.0, tick_step=25.0)
straight_chart.draw(xy=(71.0, 6.0))
straight_chart.draw_legend(xy=(80.0, 45.0), text_style=Styles.DarkBold.patch(text_size=10.0), orientation="horizontal")

save()
  • Straight vs. Smooth Curves (smooth):
    • smooth=False (default): Connects category vertices with crisp, straight polygonal line segments.
    • smooth=True: Renders organic, rounded curves through data vertices (when 3 or more points are present).
  • Vertex Markers & Per-Series Overrides (show_points, point_shape, point_size):
    • Chart-level point_shape ("circle", "square", "none") and point_size (0.7 default) apply to all series unless overridden in add_series(..., point_shape=..., point_size=...).
    • Setting point_shape="none" on a specific series suppresses both its vertex markers and its value_text_style labels—ideal for flat target or threshold reference lines.
  • Stroke Patterns (line_style): Supports "solid", "dashed", "dotted", and "dashdot".
  • Vertex Value Annotations (value_text_style): When provided (not None), formats each vertex value using y_axis.format_value(v) and renders it directly above the marker.

2. Quick Example: Smooth Spline User Growth Trends

from drawlib.canvas import save, setup
from drawlib.charts.line import LineChart
from drawlib.styles import Styles

setup(width=100, height=68)

chart = LineChart(
    axis_line_style=Styles.MutedDashed,
    categories=["Jan", "Feb", "Mar", "Apr", "May", "Jun"],
    axis_text_style=Styles.Muted.patch(text_size=10.5),
    grid_style=Styles.MutedThin,
    width=82,
    height=45,
    title="Monthly Active Users (k)",
    title_style=Styles.BlackBold.patch(text_size=13.0),
    smooth=True,
    show_points=True,
)
chart.add_series("2025", [45, 52, 58, 65, 72, 80], style=Styles.DarkFlat, line_width=2.5, line_style="dashed")
chart.add_series("2026", [60, 75, 88, 110, 135, 160], style=Styles.PrimaryFlat, line_width=2.5)

chart.draw(xy=(9, 7))
chart.draw_legend(xy=(25, 57), text_style=Styles.Muted.patch(text_size=10.5), orientation="horizontal")
save()
line_2
User Growth Trends with LineChart

3. Straight Segments, Custom Markers, Stroke Styles & Vertex Labels

By combining smooth=False (straight segments) with value_text_style, per-series point_shape ("square", "circle", "none"), and distinct line_style patterns ("solid", "dotted", "dashdot"), you can plot telemetry metrics alongside SLA thresholds:

from drawlib.canvas import save, setup
from drawlib.charts.line import LineChart
from drawlib.styles import Styles

setup(width=110, height=70)

chart = LineChart(
    axis_line_style=Styles.MutedDashed,
    categories=["00:00", "04:00", "08:00", "12:00", "16:00", "20:00"],
    width=88.0,
    height=48.0,
    title="API Gateway p95 Latency & Alert Thresholds",
    title_style=Styles.BlackBold.patch(text_size=13.0),
    smooth=False,
    show_points=True,
    axis_text_style=Styles.Muted.patch(text_size=10.5),
    grid_style=Styles.MutedThin,
    value_text_style=Styles.DarkBold.patch(text_size=10.0),
)
chart.add_series(
    "Primary Region (p95)",
    [24.0, 20.0, 46.0, 68.0, 54.0, 32.0],
    style=Styles.PrimaryFlat,
    line_width=2.2,
    point_shape="square",
    point_size=0.8,
)
chart.add_series(
    "Failover Replica",
    [18.0, 15.0, 30.0, 42.0, 35.0, 22.0],
    style=Styles.SecondaryFlat,
    line_width=2.0,
    line_style="dotted",
    point_shape="none",
)
chart.add_series(
    "SLO Ceiling (80 ms)",
    [80.0, 80.0, 80.0, 80.0, 80.0, 80.0],
    style=Styles.DarkFlat,
    line_width=1.8,
    line_style="dashdot",
    point_shape="none",
)

chart.configure_y_axis(min_value=0.0, max_value=100.0, tick_step=20.0, format="{:.0f}", unit="ms")
chart.draw(xy=(11.0, 8.0))
chart.draw_legend(
    xy=(13.0, 60.5),
    text_style=Styles.Muted.patch(text_size=10.0),
    orientation="horizontal",
    swatch_width=2.6,
    swatch_height=1.2,
    item_gap=4.0,
)
save()
line_3
Straight Line Segments with Square Vertex Markers, Value Labels, and Dashdot/Dotted Thresholds

4. API Reference

Constructor (LineChart)

All constructor arguments are keyword-only (*):

from drawlib.charts.line import Axis, DrawDirection, FormatterType, LineChart, LineStyle, PointShape, Series

chart = LineChart(
    *,
    axis_line_style: Style,
    categories: list[str],
    width: float = 80.0,
    height: float = 50.0,
    show_points: bool = True,
    point_shape: PointShape = "circle",
    point_size: float = 0.7,
    smooth: bool = False,
    axis_text_style: Style | None = None,
    grid_style: Style | None = None,
    value_text_style: Style | None = None,
    background_style: Style | None = None,
    title: str = "",
    title_style: Style | None = None,
)
Parameter Type Default Description
axis_line_style Style Required Mandatory style anchor for the coordinate baseline stroke.
categories list[str] Required Ordered category labels along the horizontal X-axis.
width / height float 80.0 / 50.0 Total bounding box dimensions of the chart in canvas units.
show_points bool True Whether to render markers at vertex coordinates.
point_shape "circle" | "square" | "none" "circle" Default vertex marker shape (PointShape).
point_size float 0.7 Default marker radius (or half-width for squares) in canvas units.
smooth bool False When True, interpolates smooth curved segments through vertices.
axis_text_style Style | None None Style for Y-axis tick labels and X-axis category names. If None, labels are omitted.
grid_style Style | None None Style for horizontal Y-axis gridlines. If None, gridlines are omitted.
value_text_style Style | None None Style for numeric labels drawn above vertex markers. If None, value labels are omitted.
background_style Style | None None Style for the outer chart background card. If None, card is omitted.
title str "" Chart title text rendered at the top of the container.
title_style Style | None None Typography style for title. Required for the title to render.

Methods & Properties

  • add_series(name: str, values: list[float], style: Style, line_width: float = 2.0, line_style: LineStyle = "solid", point_shape: PointShape | None = None, point_size: float | None = None, legend_text_style: Style | None = None, *, show: bool = True, draw_ratio: float = 1.0, draw_direction: DrawDirection = "left_to_right") -> Series: Registers a line series and returns the mutable Series instance. line_style accepts "solid", "dashed", "dotted", or "dashdot". point_shape and point_size override chart-level defaults for that series.
  • configure_y_axis(...) -> Axis / configure_x_axis(...) -> Axis: Configures the vertical value axis (scale, min_value, max_value, ticks, tick_step, format, unit, label) or horizontal category axis (show_axis_line, line_style, tick_label_style). See Axes, Scales & Legends.
  • get_size() -> tuple[float, float]: Returns (width, height) of the chart container.
  • draw(xy: tuple[float, float] = (0.0, 0.0), *, width: float | None = None, height: float | None = None, scale: float = 1.0) -> None: Renders the chart anchored at bottom-left xy, with optional temporary size overrides and proportional scale.
  • draw_legend(xy: tuple[float, float], text_style: Style, orientation: Literal["vertical", "horizontal"] = "vertical", swatch_width: float = 2.4, swatch_height: float = 1.2, item_gap: float = 4.0, *, scale: float = 1.0) -> None: Renders the decoupled series legend at xy.
  • Properties:
    • chart.series -> list[Series]: Returns a copy of registered Series objects.
    • chart.x_axis -> Axis / chart.y_axis -> Axis: Direct access to the horizontal and vertical Axis instances.