Fix precision rounding issues in LineWrapper (foliojs#1583)

Handle JS quirks with large decimal precision checks resulting from the calculations of next lines in the LineWrapper

Author: hollandjake

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## pdfkit changelog
 
+### Unreleased
+
+- Fix precision rounding issues in LineWrapper
+
 ### [v0.16.0] - 2024-12-29
 
 - Update fontkit to 2.0

lib/line_wrapper.js

@@ -1,5 +1,6 @@
 import { EventEmitter } from 'events';
 import LineBreaker from 'linebreak';
+import { PDFNumber } from './utils';
 
 const SOFT_HYPHEN = '\u00AD';
 const HYPHEN = '-';
@@ -26,9 +27,9 @@ class LineWrapper extends EventEmitter {
     // calculate the maximum Y position the text can appear at
     if (options.height != null) {
       this.height = options.height;
-      this.maxY = this.startY + options.height;
+      this.maxY = PDFNumber(this.startY + options.height);
     } else {
-      this.maxY = this.document.page.maxY();
+      this.maxY = PDFNumber(this.document.page.maxY());
     }
 
     // handle paragraph indents
@@ -230,7 +231,7 @@ class LineWrapper extends EventEmitter {
         if (
           this.height != null &&
           this.ellipsis &&
-          this.document.y + lh * 2 > this.maxY &&
+          PDFNumber(this.document.y + lh * 2) > this.maxY &&
           this.column >= this.columns
         ) {
           if (this.ellipsis === true) {
@@ -274,7 +275,7 @@ class LineWrapper extends EventEmitter {
 
         // if we've reached the edge of the page,
         // continue on a new page or column
-        if (this.document.y + lh > this.maxY) {
+        if (PDFNumber(this.document.y + lh) > this.maxY) {
           const shouldContinue = this.nextSection();
 
           // stop if we reached the maximum height

lib/utils.js

@@ -0,0 +1,6 @@
+export function PDFNumber(n) {
+  // PDF numbers are strictly 32bit
+  // so convert this number to the nearest 32bit number
+  // @see ISO 32000-1 Annex C.2 (real numbers)
+  return Math.fround(n);
+}

tests/unit/line_wrapper.spec.js

@@ -0,0 +1,62 @@
+import PDFDocument from "../../lib/document";
+import LineWrapper from '../../lib/line_wrapper';
+
+describe("LineWrapper", () => {
+  let document;
+
+  beforeEach(() => {
+    document = new PDFDocument({
+      compress: false,
+      margin: 0,
+    });
+  });
+
+  test("ellipsis is present only on last line of multiline text", () => {
+    // There is a weird edge case where ellipsis occurs on lines
+    // in the middle of text due to number rounding errors
+    //
+    // There is probably a simpler combination of values but this is one I found in the wild
+    document.y = 402.1999999999999;
+    document.fontSize(7.26643598615917)
+    const wrapper = new LineWrapper(document, {width: 300, height: 50.399999999999864, ellipsis: true})
+    let wrapperOutput = "";
+    wrapper.on("line", (buffer) => {
+      wrapperOutput += buffer;
+      document.y += document.currentLineHeight(true)
+    })
+    wrapper.wrap("- A\n- B\n- C\n- D\n- E\n- F", {})
+    expect(wrapperOutput).toBe("- A\n- B\n- C\n- D\n- E\n- F");
+  })
+
+  test("line break is handled correctly when at weird heights", () => {
+    // There is probably a simpler combination of values but this is one I found in the wild
+    document.y = 1/3;
+    document.fontSize(Math.fround(42.3/3));
+    let lineHeight = document.currentLineHeight(true);
+    const wrapper = new LineWrapper(document, {width: 300, height:lineHeight*3})
+    let wrapperOutput = "";
+    wrapper.on("line", (buffer) => {
+      wrapperOutput += buffer;
+      document.y += lineHeight
+    })
+    // Limit to 3/4 lines
+    wrapper.wrap("A\nB\nC\nD", {})
+    expect(wrapperOutput).toBe("A\nB\nC\n");
+  });
+
+  test("line break is handled correctly with ellipsis", () => {
+    // There is probably a simpler combination of values but this is one I found in the wild
+    document.y = 1/3;
+    document.fontSize(Math.fround(42.3/3));
+    let lineHeight = document.currentLineHeight(true);
+    const wrapper = new LineWrapper(document, {width: 300, height:lineHeight*3, ellipsis: true})
+    let wrapperOutput = "";
+    wrapper.on("line", (buffer) => {
+      wrapperOutput += buffer;
+      document.y += lineHeight
+    })
+    // Limit to 3/4 lines
+    wrapper.wrap("A\nB\nC\nD", {})
+    expect(wrapperOutput).toBe("A\nB\nC…");
+  });
+});