akselharting library

aksel is a charting library that provides coordinate transformations and scale mappings for data visualization. It focuses on the mathematical foundations of charting: mapping data values to screen coordinates and generating axis tick marks.

Core Concepts

Scales

Scales map data values (domain) to a normalized [0, 1] range. They support:

• Linear and logarithmic mappings
• Pan and zoom operations
• Automatic tick generation for axis labels
• Bidirectional mapping (normalize and denormalize)

Available scale types:

• [scale::Linear] - Affine mapping for linear data
• [scale::Logarithmic] - Logarithmic mapping for exponential data

Transforms

Transforms connect scales to screen coordinates, converting between:

• [PlotPoint] - Data values in chart space
• [ScreenPoint] - Pixel coordinates in screen space

The [Transform] type handles y-axis inversion (screen coordinates typically increase downward, while chart coordinates increase upward).

Examples

Basic Linear Scale

use aksel::{Scale, scale::Linear};

// Create a scale mapping [0.0, 100.0] to [0.0, 1.0]
let scale = Linear::<f64, f64>::new(0.0, 100.0);

// Normalize values to [0.0, 1.0]
assert_eq!(scale.normalize(&0.0), 0.0);
assert_eq!(scale.normalize(&50.0), 0.5);
assert_eq!(scale.normalize(&100.0), 1.0);

// Denormalize back to domain
assert_eq!(scale.denormalize(0.5), 50.0);

Pan and Zoom

use aksel::{Scale, scale::Linear};

let mut scale = Linear::<f64, f64>::new(0.0, 100.0);

// Pan by 10% (shifts by 10 units)
scale.pan(0.1);
assert_eq!(scale.domain(), (&10.0, &110.0));

// Zoom in by 2x at center
let mut scale = Linear::<f64, f64>::new(0.0, 100.0);
scale.zoom(2.0, Some(0.5));
assert_eq!(scale.domain(), (&25.0, &75.0));

Coordinate Transformation

use aksel::{Transform, scale::Linear, ScreenRect, PlotPoint};

let x_scale = Linear::<f64, f32>::new(0.0, 100.0);
let y_scale = Linear::<f64, f32>::new(0.0, 50.0);
let screen = ScreenRect { x: 0.0, y: 0.0, width: 800.0, height: 400.0 };

let transform = Transform::new(&screen, &x_scale, &y_scale);

// Convert plot coordinates to screen pixels
let plot_point = PlotPoint::new(50.0, 25.0);
let screen_point = transform.chart_to_screen(&plot_point);
// screen_point is at (400.0, 200.0) - center of screen

Generating Ticks

use aksel::{Scale, scale::Linear};

let scale = Linear::<f64, f64>::new(0.0, 100.0);
let ticks = scale.ticks();

// Ticks include both major (level 0) and minor (level 1) marks
for tick in ticks {
    if tick.level == 0 {
        println!("Major tick at: {}", tick.value);
    }
}