feuerwerk/tests/viewport/nine-slice.test.ts

import { describe, expect, it } from 'vitest';
import type { NineSlice } from '../../src/core/model/texture';
import { MAX_TILES, sliceGeometry, sliceKey, sliceSpans } from '../../src/viewport/nineSlice';

const slice = (border: Partial<NineSlice['border']>, fill: NineSlice['fill'] = 'stretch'): NineSlice => ({
  border: { left: 0, top: 0, right: 0, bottom: 0, ...border },
  fill,
  sourceW: 24,
  sourceH: 24,
});

describe('sliceSpans', () => {
  it('keeps the corners at their source size and gives the rest to the middle', () => {
    const spans = sliceSpans(200, 24, 8, 8, 'stretch');
    expect(spans.map((s) => [s.p0, s.p1])).toEqual([
      [0, 8],
      [8, 192],
      [192, 200],
    ]);
    // The UVs cut the frame at the same pixels, so the corner shows the corner.
    expect(spans.map((s) => [s.t0, s.t1])).toEqual([
      [0, 1 / 3],
      [1 / 3, 2 / 3],
      [2 / 3, 1],
    ]);
  });

  it('leaves out a part that has no room: a border of zero is no quad at all', () => {
    expect(sliceSpans(200, 24, 0, 8, 'stretch').map((s) => [s.p0, s.p1])).toEqual([
      [0, 192],
      [192, 200],
    ]);
    // Exactly as wide as its two borders: middle gone, the two corners meet.
    expect(sliceSpans(16, 24, 8, 8, 'stretch').map((s) => [s.p0, s.p1])).toEqual([
      [0, 8],
      [8, 16],
    ]);
  });

  it('scales both borders down together when the sprite is smaller than they are', () => {
    const spans = sliceSpans(8, 24, 8, 8, 'stretch');
    // Never overlapping corners: 4 + 4 rather than 8 + 8 on a box of 8.
    expect(spans.map((s) => [s.p0, s.p1])).toEqual([
      [0, 4],
      [4, 8],
    ]);
    // The UVs are untouched by the squeeze: each corner still shows its own eight pixels.
    expect(spans.map((s) => [s.t0, s.t1])).toEqual([
      [0, 1 / 3],
      [2 / 3, 1],
    ]);
  });

  it('repeats the middle in whole tiles of the frame and cuts the last one', () => {
    const spans = sliceSpans(50, 24, 8, 8, 'repeat');
    const middle = spans.slice(1, -1);
    expect(middle.map((s) => [s.p0, s.p1])).toEqual([
      [8, 16],
      [16, 24],
      [24, 32],
      [32, 40],
      [40, 42],
    ]);
    // The cut tile shows only as much of the picture as it covers – a quarter of the eight pixels.
    expect(middle.at(-1)?.t1).toBeCloseTo(1 / 3 + (2 / 8) * (1 / 3), 10);
    // Every tile starts at the middle's own first pixel; none samples past the frame.
    expect(middle.every((s) => s.t0 === 1 / 3 && s.t1 <= 2 / 3)).toBe(true);
  });

  it('stretches rather than building a tile for every pixel of a huge sprite', () => {
    // A middle of 14 source pixels: exactly `MAX_TILES` of them still tile, one more stretches.
    const many = sliceSpans(10 + MAX_TILES * 14, 24, 5, 5, 'repeat');
    expect(many.length).toBe(2 + MAX_TILES);
    const tooMany = sliceSpans(10 + (MAX_TILES + 1) * 14, 24, 5, 5, 'repeat');
    expect(tooMany.length).toBe(3);
  });

  it('answers nothing for a box or a picture of no size', () => {
    expect(sliceSpans(0, 24, 8, 8, 'stretch')).toEqual([]);
    expect(sliceSpans(200, 0, 8, 8, 'stretch')).toEqual([]);
  });
});

describe('sliceGeometry', () => {
  it('builds one quad per part, in the 0..1 box the unit quad covers', () => {
    const { positions, uvs, indices } = sliceGeometry(
      slice({ left: 8, top: 8, right: 8, bottom: 8 }),
      200,
      200,
    );
    expect(indices.length).toBe(9 * 6);
    expect(positions.length).toBe(9 * 8);
    expect(uvs.length).toBe(positions.length);
    // Fractions, not units: the sprite's size lives in the mesh's scale.
    expect(Math.min(...positions)).toBe(0);
    expect(Math.max(...positions)).toBe(1);
    // The first quad is the top-left corner: 8 of 200 units, showing 8 of 24 pixels.
    // Close, not equal: the buffers are Float32, where neither 0.04 nor a third is exact.
    expect(positions[2]).toBeCloseTo(0.04, 6);
    expect(uvs[2]).toBeCloseTo(1 / 3, 6);
    expect([positions[0], positions[1], positions[3]]).toEqual([0, 0, 0]);
  });

  it('drops the rows and columns that have no room, keeping the quads rectangular', () => {
    const { indices } = sliceGeometry(slice({ left: 8, right: 8 }), 200, 200);
    // Three columns, one row – nothing is cut horizontally.
    expect(indices.length).toBe(3 * 6);
  });
});

describe('sliceKey', () => {
  it('changes with anything the geometry is built from, and not with a sub-pixel of size', () => {
    const base = slice({ left: 8, right: 8 });
    expect(sliceKey(base, 200, 100)).toBe(sliceKey(base, 200.1, 100));
    expect(sliceKey(base, 200, 100)).not.toBe(sliceKey(base, 201, 100));
    expect(sliceKey(base, 200, 100)).not.toBe(sliceKey(slice({ left: 8, right: 7 }), 200, 100));
    expect(sliceKey(base, 200, 100)).not.toBe(sliceKey(slice({ left: 8, right: 8 }, 'repeat'), 200, 100));
  });
});