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Increase test coverage #91

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May 3, 2024
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Increase test coverage #91

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190 changes: 190 additions & 0 deletions test/layout-test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,138 @@ function itemsFromString(s: string, charWidth: number, glueStretch: number): Tex
return items;
}

function charWidth(char: string): number {
// Traditional Monotype character widths in machine units (1/18th of an em)
// from p. 75 of Digital Typography
if (char.length !== 1) {
throw new Error(`Input is not a single character: ${char}`);
}
switch (char) {
case 'i':
case 'l':
case ',':
case '.':
case ';':
case '’':
return 5;
case 'f':
case 'j':
case 'I':
case '-':
case '\u00ad':
return 6;
case 'r':
case 's':
case 't':
return 7;
case 'c':
case 'e':
case 'z':
return 8;
case 'a':
case 'g':
case 'o':
case 'v':
return 9;
case 'b':
case 'd':
case 'h':
case 'k':
case 'n':
case 'p':
case 'q':
case 'u':
case 'x':
case 'y':
return 10;
case 'w':
case 'C':
return 13;
case 'm':
return 15;
default:
throw new Error(`Unsupported character: ${char.charCodeAt(0)}`);
}
}

function frogPrinceItemsImpl(
text: string,
prologue: TextInputItem[],
betweenWords: (c: string) => TextInputItem[],
epilogue: TextInputItem[],
): TextInputItem[] {
const result: TextInputItem[] = [];
let buf = '';
let width = 0;
let lastC = '*';

result.push(...prologue);

for (const c of text) {
if (['-', '\u00AD', ' '].includes(c)) {
if (buf !== '') {
result.push({ type: 'box', width, text: buf } as TextBox);
buf = '';
width = 0;
}
}

switch (c) {
case ' ':
result.push(...betweenWords(lastC));
break;
case '-':
result.push({ type: 'box', width: charWidth(c), text: '-' } as TextBox);
result.push({ type: 'penalty', width: 0, cost: 50, flagged: true });
break;
case '\u00AD':
// Soft hyphen
result.push({ type: 'penalty', width: charWidth(c), cost: 50, flagged: true });
break;
default:
buf += c;
width += charWidth(c);
break;
}

lastC = c;
}

if (buf !== '') {
result.push({ type: 'box', width, text: buf });
}

result.push(...epilogue);

return result;
}

const frogPrinceText =
'In olden times when wish\u00ading still helped one, there lived a king whose daugh\u00adters were all beau\u00adti\u00adful; and the young\u00adest was so beau\u00adti\u00adful that the sun it\u00adself, which has seen so much, was aston\u00adished when\u00adever it shone in her face. Close by the king’s castle lay a great dark for\u00adest, and un\u00adder an old lime-tree in the for\u00adest was a well, and when the day was very warm, the king’s child went out into the for\u00adest and sat down by the side of the cool foun\u00adtain; and when she was bored she took a golden ball, and threw it up on high and caught it; and this ball was her favor\u00adite play\u00adthing.';

function frogPrinceItems(): TextInputItem[] {
// Built as described on p. 75 of Digital Typography
const prologue: TextInputItem[] = [];
const betweenWords = (c: string): TextInputItem[] => {
switch (c) {
case ',':
return [{ type: 'glue', width: 6, stretch: 4, shrink: 2, text: ' ' } as TextGlue];
case ';':
return [{ type: 'glue', width: 6, stretch: 4, shrink: 1, text: ' ' } as TextGlue];
case '.':
return [{ type: 'glue', width: 8, stretch: 6, shrink: 1, text: ' ' } as TextGlue];
default:
return [{ type: 'glue', width: 6, stretch: 3, shrink: 2, text: ' ' } as TextGlue];
}
};
const epilogue: TextInputItem[] = [
{ type: 'penalty', width: 0, cost: 1000, flagged: false },
{ type: 'glue', width: 0, stretch: 1000, shrink: 0, text: '' } as TextGlue,
{ type: 'penalty', width: 0, cost: -1000, flagged: true },
];
return frogPrinceItemsImpl(frogPrinceText, prologue, betweenWords, epilogue);
}

describe('layout', () => {
describe('breakLines', () => {
it('returns an empty list if the input is empty', () => {
Expand All @@ -119,6 +251,64 @@ describe('layout', () => {
assert.deepEqual(breakpoints, [0]);
});

it('generates narrow frog prince layout from p. 81 of Digital Typography', () => {
const items = frogPrinceItems();
// width given on p. 78 of Digital Typography
// subtract 1em (18 machine units) from the first line
const lineLengths = [372, ...Array(items.length - 1).fill(390)];
const breakpoints = breakLines(items, lineLengths);
const lines = lineStrings(items, breakpoints);
assert.deepEqual(lines, [
'In olden times when wishing still helped one,',
'there lived a king whose daughters were all beau-',
'tiful; and the youngest was so beautiful that the',
'sun itself, which has seen so much, was aston-',
'ished whenever it shone in her face. Close by the',
'king’s castle lay a great dark forest, and under an',
'old limetree in the forest was a well, and when',
'the day was very warm, the king’s child went out',
'into the forest and sat down by the side of the',
'cool fountain; and when she was bored she took a',
'golden ball, and threw it up on high and caught',
'it; and this ball was her favorite plaything. -',
]);
const adjRatios = adjustmentRatios(items, lineLengths, breakpoints).map((num) =>
Number(num.toFixed(3)),
);
assert.deepEqual(
adjRatios,
[0.857, 0.0, 0.28, 1.0, 0.067, -0.278, 0.536, -0.167, 0.7, -0.176, 0.357, 0.049],
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I'm not certain it is guaranteed that these float literals will be converted to the exact same float values as the result of parsing the truncated number, in all environments. If a problem is encountered, assert.closeTo could be used.

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I thought about using closeTo, but there wasn't a deepCloseTo like there is a deepEqual so I would have had to iterate over the list. Happy to switch to that approach if you think it is preferable.

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I'm happy to leave this as-is. My concern is only theoretical at the moment.

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I notice the book image shows 0.000 as the final adjustment ratio rather than 0.049. Do you know the reason for that? Does it matter at all?

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This is because you define MAX_COST to be 1000, but Knuth & Plass's calculations are based on a MAX_COST of 100,000. I chose to be consistent with the rest of the code in this repository, but if you want to be truly faithful to the book I can submit this PR with passing tests:

diff --git a/test/layout-test.ts b/test/layout-test.ts
index 2a0f21d..1e0d274 100644
--- a/test/layout-test.ts
+++ b/test/layout-test.ts
@@ -232,9 +232,9 @@ function frogPrinceItems(): TextInputItem[] {
     }
   };
   const epilogue: TextInputItem[] = [
-    { type: 'penalty', width: 0, cost: 1000, flagged: false },
-    { type: 'glue', width: 0, stretch: 1000, shrink: 0, text: '' } as TextGlue,
-    { type: 'penalty', width: 0, cost: -1000, flagged: true },
+    { type: 'penalty', width: 0, cost: 100000, flagged: false },
+    { type: 'glue', width: 0, stretch: 100000, shrink: 0, text: '' } as TextGlue,
+    { type: 'penalty', width: 0, cost: -100000, flagged: true },
   ];
   return frogPrinceItemsImpl(frogPrinceText, prologue, betweenWords, epilogue);
 }
@@ -277,7 +277,7 @@ describe('layout', () => {
       );
       assert.deepEqual(
         adjRatios,
-        [0.857, 0.0, 0.28, 1.0, 0.067, -0.278, 0.536, -0.167, 0.7, -0.176, 0.357, 0.049],
+        [0.857, 0.0, 0.28, 1.0, 0.067, -0.278, 0.536, -0.167, 0.7, -0.176, 0.357, 0.0],
       );
     });
 
@@ -305,7 +305,7 @@ describe('layout', () => {
       );
       assert.deepEqual(
         adjRatios,
-        [0.774, 0.179, 0.629, 0.545, 0.0, 0.079, 0.282, 0.294, 0.575, 0.353],
+        [0.774, 0.179, 0.629, 0.545, 0.0, 0.079, 0.282, 0.294, 0.575, 0.004],
       );
     });

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This is because you define MAX_COST to be 1000, but Knuth & Plass's calculations are based on a MAX_COST of 100,000.

Ah, thanks for the clarification. That's fine to leave as-is for the moment then.

);
});

it('generates wide frog prince layout from p. 82 of Digital Typography', () => {
const items = frogPrinceItems();
// width given on p. 81 of Digital Typography
// subtract 1em (18 machine units) from the first line
const lineLengths = [482, ...Array(items.length - 1).fill(500)];
const breakpoints = breakLines(items, lineLengths);
const lines = lineStrings(items, breakpoints);
assert.deepEqual(lines, [
'In olden times when wishing still helped one, there lived a',
'king whose daughters were all beautiful; and the youngest was',
'so beautiful that the sun itself, which has seen so much, was',
'astonished whenever it shone in her face. Close by the king’s',
'castle lay a great dark forest, and under an old limetree in the',
'forest was a well, and when the day was very warm, the king’s',
'child went out into the forest and sat down by the side of the',
'cool fountain; and when she was bored she took a golden ball,',
'and threw it up on high and caught it; and this ball was her',
'favorite plaything. -',
]);
const adjRatios = adjustmentRatios(items, lineLengths, breakpoints).map((num) =>
Number(num.toFixed(3)),
);
assert.deepEqual(
adjRatios,
[0.774, 0.179, 0.629, 0.545, 0.0, 0.079, 0.282, 0.294, 0.575, 0.353],
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The last adjustment ratio value also differs from the book here.

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Ditto

);
});

it('generates expected layout', () => {
const f = readLayoutFixture(fixture);
f.outputs.forEach(({ lines, layoutOptions }) => {
Expand Down
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