Alto \ Scale

A strict, mathematical engine for Modular Scales. It handles the arithmetic of progressions, designed for generative design, typography engines, and rhythmic computation.

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Installation

composer require alto/scale

Core Concepts

1. The Scale Facade

Use the Scale facade for fluent instantiation of any scale type.

use Alto\Scale\Scale;
use Alto\Scale\Ratio;

// Modular (Geometric): Base 16px, Ratio 1.25 (Major Third)
$type = Scale::majorThird(16.0);

// Linear (Arithmetic): Base 0, Increment 8
$grid = Scale::linear(0, 8);

// Fibonacci: Using Binet's formula
$fib = Scale::fibonacci();

// Multi-Strand: Interleaved scales (e.g., 16px and 12px strands)
$strands = Scale::strands([16, 12], Ratio::PerfectFifth);

2. Computing Values

All scales implement the ScaleInterface and are IteratorAggregate.

echo $type->get(0);  // 16.0
echo $type->get(1);  // 20.0
echo $type->get(-1); // 12.8

// ModularScale is callable
echo $type(2); // 25.0

Snapping (Normalization)

Find the nearest mathematical step for any arbitrary value.

// Returns 20.0 (The nearest step on a Major Third scale starting at 16)
$value = $type->snap(19.8);

Iteration & Ranges

// Scales are iterable (defaults to steps 0-10)
foreach ($type as $step => $value) {
    // ...
}

// Custom ranges
$values = $type->range(-2, 2);
// Returns: [-2 => 10.24, -1 => 12.8, 0 => 16.0, 1 => 20.0, 2 => 25.0]

3. The Guesser (Reverse Engineering)

Analyze messy datasets to find their underlying mathematical scale.

use Alto\Scale\Scale;
use Alto\Scale\ScaleGuesser;

$messyValues = [15.9, 20.1, 24.8, 31.5];

// Via the facade
$scale = Scale::guess($messyValues);

// Or directly with custom tolerance
$guesser = new ScaleGuesser(tolerance: 0.05);
$scale = $guesser->guess($messyValues);

// Align values to the guessed (or provided) scale
$aligned = $guesser->align($messyValues);

4. The Linter (Audit & Fix)

Audit datasets for scale compliance and automatically harmonize them.

use Alto\Scale\ScaleLinter;
use Alto\Scale\Scale;

$linter = new ScaleLinter(Scale::linear(0, 8));

// Get a detailed compliance report
$report = $linter->lint([8, 15, 24]);
// Each entry: ['original', 'suggested', 'step', 'deviation', 'isValid']

// Returns [8.0, 16.0, 24.0]
$fixed = $linter->fix([8, 15, 24]);

API Reference

Alto\Scale\Scale (Facade)

Method	Returns
modular(float $base, float|Ratio $ratio)	ModularScale
linear(float $base, float $increment)	LinearScale
fibonacci(float $multiplier)	FibonacciScale
strands(array $bases, float|Ratio $ratio)	MultiStrandScale
guess(array $values)	ModularScale
majorThird(float $base)	ModularScale
perfectFifth(float $base)	ModularScale
golden(float $base)	ModularScale

Alto\Scale\ScaleInterface

All scale classes (ModularScale, LinearScale, FibonacciScale, MultiStrandScale) implement:

Method	Description
get(int $step): float	Get the value at a specific step
stepOf(float $value): int	Find the closest step index for a value
snap(float $value): float	Snap a value to the nearest step
range(int $min, int $max): array	Generate values between steps

Alto\Scale\ModularScale

Geometric progression: value = base * (ratio ^ step)

Method	Description
areHarmonic(float $a, float $b, float $epsilon): bool	Check if two values are harmonically related
withBase(float $base): self	Create a new scale with a different base
withRatio(float|Ratio $ratio): self	Create a new scale with a different ratio
shift(int $steps): self	Create a new scale shifted by N steps

Alto\Scale\LinearScale

Arithmetic progression: value = base + (step * increment)

Alto\Scale\FibonacciScale

Fibonacci sequence using Binet's formula, with optional multiplier.

Alto\Scale\MultiStrandScale

Interleaved modular scales sharing a common ratio, useful for multi-strand typographic scales.

Alto\Scale\ScaleGuesser

Method	Description
guess(array $values): ModularScale	Infer a modular scale from values
align(array $values, ?ScaleInterface $scale): array	Snap all values to a scale

Alto\Scale\ScaleLinter

Method	Description
lint(array $values): array	Audit values against a scale
fix(array $values): array	Harmonize values to the scale

Alto\Scale\Ratio (Enum)

Standard musical/typographic ratios:

Ratio	Value
MinorSecond	1.067
MajorSecond	1.125
MinorThird	1.200
MajorThird	1.250
PerfectFourth	1.333
AugmentedFourth	1.414
PerfectFifth	1.500
MinorSixth	1.600
GoldenRatio	1.618
MajorSixth	1.667
MinorSeventh	1.778
MajorSeventh	1.875
Octave	2.000

License

This project is licensed under the MIT License.