fix: footnotes rendering causing lines to shift, other footnote rendering issues

packages/layout-engine/contracts/src/index.ts

@@ -39,6 +39,16 @@ export {
   formatInsetClipPathTransform,
   type InsetClipPathScale,
 } from './clip-path-inset.js';
+export {
+  SUBSCRIPT_SUPERSCRIPT_SCALE,
+  normalizeBaselineShift,
+  hasExplicitBaselineShift,
+  isSuperscriptOrSubscript,
+  usesDefaultScriptLayout,
+  scaleFontSizeForVerticalText,
+  resolveBaseFontSizeForVerticalText,
+  type VerticalTextAlign,
+} from './vertical-text.js';
 
 export { computeFragmentPmRange, computeLinePmRange, type LinePmRange } from './pm-range.js';
 export { cloneColumnLayout, normalizeColumnLayout, widthsEqual } from './column-layout.js';
@@ -200,7 +210,10 @@ export type RunMarks = {
   textTransform?: 'uppercase' | 'lowercase' | 'capitalize' | 'none';
   /** Vertical alignment for superscript/subscript text. */
   vertAlign?: 'superscript' | 'subscript' | 'baseline';
-  /** Custom baseline shift in points (positive = raise, negative = lower). Takes precedence over vertAlign for positioning. */
+  /**
+   * Explicit baseline shift in points (positive = raise, negative = lower).
+   * Rendering normalizes a shift of zero to "no explicit shift".
+   */
   baselineShift?: number;
 };
 

packages/layout-engine/contracts/src/vertical-text.test.ts

@@ -0,0 +1,179 @@
+import { describe, expect, it } from 'vitest';
+import {
+  SUBSCRIPT_SUPERSCRIPT_SCALE,
+  normalizeBaselineShift,
+  hasExplicitBaselineShift,
+  isSuperscriptOrSubscript,
+  usesDefaultScriptLayout,
+  scaleFontSizeForVerticalText,
+  resolveBaseFontSizeForVerticalText,
+} from './vertical-text.js';
+
+describe('normalizeBaselineShift', () => {
+  it('returns undefined for null', () => {
+    expect(normalizeBaselineShift(null)).toBeUndefined();
+  });
+
+  it('returns undefined for undefined', () => {
+    expect(normalizeBaselineShift(undefined)).toBeUndefined();
+  });
+
+  it('returns undefined for NaN', () => {
+    expect(normalizeBaselineShift(NaN)).toBeUndefined();
+  });
+
+  it('returns undefined for Infinity', () => {
+    expect(normalizeBaselineShift(Infinity)).toBeUndefined();
+  });
+
+  it('returns undefined for zero (identity value)', () => {
+    expect(normalizeBaselineShift(0)).toBeUndefined();
+  });
+
+  it('returns undefined for near-zero values within epsilon', () => {
+    expect(normalizeBaselineShift(1e-7)).toBeUndefined();
+    expect(normalizeBaselineShift(-1e-7)).toBeUndefined();
+  });
+
+  it('returns the value for positive shifts', () => {
+    expect(normalizeBaselineShift(3)).toBe(3);
+  });
+
+  it('returns the value for negative shifts', () => {
+    expect(normalizeBaselineShift(-1.5)).toBe(-1.5);
+  });
+
+  it('returns the value for small but non-zero shifts', () => {
+    expect(normalizeBaselineShift(0.01)).toBe(0.01);
+  });
+});
+
+describe('hasExplicitBaselineShift', () => {
+  it('returns false for null/undefined/zero', () => {
+    expect(hasExplicitBaselineShift(null)).toBe(false);
+    expect(hasExplicitBaselineShift(undefined)).toBe(false);
+    expect(hasExplicitBaselineShift(0)).toBe(false);
+  });
+
+  it('returns true for non-zero finite values', () => {
+    expect(hasExplicitBaselineShift(3)).toBe(true);
+    expect(hasExplicitBaselineShift(-1.5)).toBe(true);
+  });
+});
+
+describe('isSuperscriptOrSubscript', () => {
+  it('returns true for superscript', () => {
+    expect(isSuperscriptOrSubscript('superscript')).toBe(true);
+  });
+
+  it('returns true for subscript', () => {
+    expect(isSuperscriptOrSubscript('subscript')).toBe(true);
+  });
+
+  it('returns false for baseline', () => {
+    expect(isSuperscriptOrSubscript('baseline')).toBe(false);
+  });
+
+  it('returns false for null/undefined', () => {
+    expect(isSuperscriptOrSubscript(null)).toBe(false);
+    expect(isSuperscriptOrSubscript(undefined)).toBe(false);
+  });
+});
+
+describe('usesDefaultScriptLayout', () => {
+  it('returns true for superscript without explicit shift', () => {
+    expect(usesDefaultScriptLayout({ vertAlign: 'superscript' })).toBe(true);
+  });
+
+  it('returns true for subscript without explicit shift', () => {
+    expect(usesDefaultScriptLayout({ vertAlign: 'subscript' })).toBe(true);
+  });
+
+  it('returns false for superscript with explicit shift', () => {
+    expect(usesDefaultScriptLayout({ vertAlign: 'superscript', baselineShift: 3 })).toBe(false);
+  });
+
+  it('returns true for superscript with zero shift (identity)', () => {
+    expect(usesDefaultScriptLayout({ vertAlign: 'superscript', baselineShift: 0 })).toBe(true);
+  });
+
+  it('returns false for baseline', () => {
+    expect(usesDefaultScriptLayout({ vertAlign: 'baseline' })).toBe(false);
+  });
+
+  it('returns false when no vertAlign', () => {
+    expect(usesDefaultScriptLayout({})).toBe(false);
+    expect(usesDefaultScriptLayout({ baselineShift: 3 })).toBe(false);
+  });
+});
+
+describe('scaleFontSizeForVerticalText', () => {
+  it('scales font size for default superscript', () => {
+    expect(scaleFontSizeForVerticalText(16, { vertAlign: 'superscript' })).toBeCloseTo(
+      16 * SUBSCRIPT_SUPERSCRIPT_SCALE,
+    );
+  });
+
+  it('scales font size for default subscript', () => {
+    expect(scaleFontSizeForVerticalText(16, { vertAlign: 'subscript' })).toBeCloseTo(16 * SUBSCRIPT_SUPERSCRIPT_SCALE);
+  });
+
+  it('does not scale when explicit shift is present', () => {
+    expect(scaleFontSizeForVerticalText(16, { vertAlign: 'superscript', baselineShift: 3 })).toBe(16);
+  });
+
+  it('scales when shift is zero (identity)', () => {
+    expect(scaleFontSizeForVerticalText(16, { vertAlign: 'superscript', baselineShift: 0 })).toBeCloseTo(
+      16 * SUBSCRIPT_SUPERSCRIPT_SCALE,
+    );
+  });
+
+  it('does not scale for baseline', () => {
+    expect(scaleFontSizeForVerticalText(16, { vertAlign: 'baseline' })).toBe(16);
+  });
+
+  it('does not scale when no vertAlign', () => {
+    expect(scaleFontSizeForVerticalText(16, {})).toBe(16);
+  });
+
+  it('passes through non-finite values unchanged', () => {
+    expect(scaleFontSizeForVerticalText(NaN, { vertAlign: 'superscript' })).toBeNaN();
+    expect(scaleFontSizeForVerticalText(Infinity, { vertAlign: 'superscript' })).toBe(Infinity);
+  });
+});
+
+describe('resolveBaseFontSizeForVerticalText', () => {
+  it('un-scales default superscript font size', () => {
+    const scaled = 16 * SUBSCRIPT_SUPERSCRIPT_SCALE;
+    expect(resolveBaseFontSizeForVerticalText(scaled, { vertAlign: 'superscript' })).toBeCloseTo(16);
+  });
+
+  it('un-scales default subscript font size', () => {
+    const scaled = 16 * SUBSCRIPT_SUPERSCRIPT_SCALE;
+    expect(resolveBaseFontSizeForVerticalText(scaled, { vertAlign: 'subscript' })).toBeCloseTo(16);
+  });
+
+  it('returns font size unchanged when explicit shift is present', () => {
+    expect(resolveBaseFontSizeForVerticalText(16, { vertAlign: 'superscript', baselineShift: 3 })).toBe(16);
+  });
+
+  it('un-scales when shift is zero (identity)', () => {
+    const scaled = 16 * SUBSCRIPT_SUPERSCRIPT_SCALE;
+    expect(resolveBaseFontSizeForVerticalText(scaled, { vertAlign: 'superscript', baselineShift: 0 })).toBeCloseTo(16);
+  });
+
+  it('returns font size unchanged for baseline', () => {
+    expect(resolveBaseFontSizeForVerticalText(16, { vertAlign: 'baseline' })).toBe(16);
+  });
+
+  it('passes through non-finite values unchanged', () => {
+    expect(resolveBaseFontSizeForVerticalText(NaN, { vertAlign: 'superscript' })).toBeNaN();
+  });
+
+  it('roundtrips with scaleFontSizeForVerticalText', () => {
+    const formatting = { vertAlign: 'superscript' as const };
+    const original = 24;
+    const scaled = scaleFontSizeForVerticalText(original, formatting);
+    expect(resolveBaseFontSizeForVerticalText(scaled, formatting)).toBeCloseTo(original);
+  });
+});

packages/layout-engine/contracts/src/vertical-text.ts

@@ -0,0 +1,78 @@
+/**
+ * Shared vertical-text helpers for superscript, subscript, and explicit baseline shifts.
+ *
+ * OOXML allows both semantic vertical alignment (`vertAlign`) and an explicit
+ * position offset (`position`). During rendering, a zero offset is an identity
+ * value and should behave the same as an absent offset.
+ */
+
+export type VerticalTextAlign = 'superscript' | 'subscript' | 'baseline';
+
+type VerticalTextFormatting = {
+  vertAlign?: VerticalTextAlign | null;
+  baselineShift?: number | null;
+};
+
+/**
+ * Font size scaling factor for default superscript/subscript rendering.
+ * Matches Microsoft Word's default visual behavior closely enough for layout.
+ */
+export const SUBSCRIPT_SUPERSCRIPT_SCALE = 0.65;
+
+const BASELINE_SHIFT_EPSILON = 1e-6;
+
+/**
+ * Normalizes explicit baseline shifts for rendering.
+ *
+ * A numeric shift of zero is a no-op and should not override semantic
+ * superscript/subscript styling. This preserves the raw OOXML value for
+ * round-tripping while giving the renderer a clean intent model.
+ */
+export function normalizeBaselineShift(baselineShift: number | null | undefined): number | undefined {
+  if (!Number.isFinite(baselineShift)) {
+    return undefined;
+  }
+
+  const normalizedShift = baselineShift as number;
+  return Math.abs(normalizedShift) <= BASELINE_SHIFT_EPSILON ? undefined : normalizedShift;
+}
+
+export function hasExplicitBaselineShift(baselineShift: number | null | undefined): boolean {
+  return normalizeBaselineShift(baselineShift) != null;
+}
+
+export function isSuperscriptOrSubscript(vertAlign: VerticalTextAlign | null | undefined): boolean {
+  return vertAlign === 'superscript' || vertAlign === 'subscript';
+}
+
+/**
+ * Returns true when the run should use the default superscript/subscript
+ * presentation path: scaled font size plus the renderer's default raise/lower.
+ */
+export function usesDefaultScriptLayout(formatting: VerticalTextFormatting): boolean {
+  return isSuperscriptOrSubscript(formatting.vertAlign) && !hasExplicitBaselineShift(formatting.baselineShift);
+}
+
+/**
+ * Applies default superscript/subscript font scaling when the run uses the
+ * default semantic layout path.
+ */
+export function scaleFontSizeForVerticalText(fontSize: number, formatting: VerticalTextFormatting): number {
+  if (!Number.isFinite(fontSize)) {
+    return fontSize;
+  }
+
+  return usesDefaultScriptLayout(formatting) ? fontSize * SUBSCRIPT_SUPERSCRIPT_SCALE : fontSize;
+}
+
+/**
+ * Returns the original base font size for runs that already carry scaled
+ * superscript/subscript text metrics.
+ */
+export function resolveBaseFontSizeForVerticalText(fontSize: number, formatting: VerticalTextFormatting): number {
+  if (!Number.isFinite(fontSize)) {
+    return fontSize;
+  }
+
+  return usesDefaultScriptLayout(formatting) ? fontSize / SUBSCRIPT_SUPERSCRIPT_SCALE : fontSize;
+}