feuerwerk/tests/ui/math.test.ts

import { describe, expect, it } from 'vitest';
import {
  clamp,
  centreY,
  formatNumber,
  NUMBER_DECIMALS,
  roundTo,
  snapToStep,
  zoomFactor,
} from '../../src/ui/math';

describe('clamp', () => {
  it('keeps a value inside the range', () => {
    expect(clamp(5, 0, 10)).toBe(5);
    expect(clamp(-1, 0, 10)).toBe(0);
    expect(clamp(11, 0, 10)).toBe(10);
  });

  it('lets the lower bound win when the range is inverted', () => {
    // A popup wider than the screen: pinning it to the left edge beats pinning it to the right.
    expect(clamp(5, 10, 0)).toBe(10);
  });
});

describe('centreY', () => {
  it('centres on whole pixels', () => {
    expect(centreY(30, 20)).toBe(5);
    expect(centreY(31, 20)).toBe(6);
  });
});

describe('formatNumber', () => {
  it('shows three decimals by default', () => {
    expect(NUMBER_DECIMALS).toBe(3);
    expect(formatNumber(100)).toBe('100.000');
    expect(formatNumber(0.5)).toBe('0.500');
    expect(formatNumber(-12)).toBe('-12.000');
  });

  it('never hides a fractional value behind a whole number', () => {
    // The bug this replaces: a field with step 1 showed a stored 100.234 as "100", and
    // committing that text wrote the rounded value back into the project.
    expect(formatNumber(100.234)).toBe('100.234');
    expect(formatNumber(0.001)).toBe('0.001');
  });

  it('rounds to the last shown place', () => {
    expect(formatNumber(1.2345)).toBe('1.234');
    expect(formatNumber(1.2356)).toBe('1.236');
  });

  it('drops the minus sign from a value that displays as zero', () => {
    expect(formatNumber(-0)).toBe('0.000');
    expect(formatNumber(-0.0001)).toBe('0.000');
  });

  it('honours an explicit precision', () => {
    expect(formatNumber(1.25, 1)).toBe('1.3');
    expect(formatNumber(1.25, 0)).toBe('1');
  });

  it('shows a field of integral values without a decimal point at all', () => {
    // What `NumberFieldOptions.decimals: 0` buys: a pixel index reads "33", not "33.000".
    expect(formatNumber(33, 0)).toBe('33');
    expect(formatNumber(-4, 0)).toBe('-4');
    // The minus-zero rule holds at every precision, not just the default one.
    expect(formatNumber(-0.4, 0)).toBe('0');
  });
});

describe('roundTo', () => {
  it('keeps a value at the precision its field shows', () => {
    // Why the field rounds instead of only formatting: a `decimals: 0` field used to display
    // "641" while the project still held 640.5.
    expect(roundTo(640.5, 0)).toBe(641);
    expect(roundTo(32.4, 0)).toBe(32);
    expect(roundTo(1.2345)).toBe(1.234);
  });

  it('removes binary-float noise', () => {
    expect(roundTo(0.30000000000000004)).toBe(0.3);
  });

  it('passes non-finite values through', () => {
    expect(roundTo(NaN)).toBeNaN();
    expect(roundTo(Infinity)).toBe(Infinity);
  });
});

describe('snapToStep', () => {
  it('lands on whole numbers for a step-1 field', () => {
    // The bug: a scrub added fractional device pixels to an already fractional value, so
    // dragging X produced values like 100.667 instead of 101.
    expect(snapToStep(100.667, 1)).toBe(101);
    expect(snapToStep(100.333, 1)).toBe(100);
    expect(snapToStep(-3.5, 1)).toBe(-3);
  });

  it('uses the increment as the grid, so a fine drag keeps its precision', () => {
    // Alt halves the step to 0.1: snapping must not swallow the fine adjustment.
    expect(snapToStep(1.24, 0.1)).toBe(1.2);
    expect(snapToStep(1.26, 0.1)).toBe(1.3);
    expect(snapToStep(3.0000000000000004, 0.1)).toBe(3);
  });

  it('passes values through when there is no grid', () => {
    expect(snapToStep(1.234, 0)).toBe(1.234);
    expect(snapToStep(1.234, -1)).toBe(1.234);
    expect(snapToStep(NaN, 1)).toBeNaN();
  });
});

describe('zoomFactor', () => {
  it('zooms in for a negative delta and out for a positive one', () => {
    expect(zoomFactor(-100)).toBeGreaterThan(1);
    expect(zoomFactor(100)).toBeLessThan(1);
    expect(zoomFactor(0)).toBe(1);
  });

  it('returns exactly to the starting zoom after scrolling back', () => {
    // Why exponential: the scene view and the graph editor both rely on this cancelling out.
    expect(1 * zoomFactor(-120) * zoomFactor(120)).toBeCloseTo(1, 12);
  });
});