Add sizeOfFontAtHeight() methods (#103)

src/core/pdf-structures/factories/PDFEmbeddedFontFactory.ts

@@ -153,7 +153,7 @@ class PDFEmbeddedFontFactory {
    * Measures the height of this font at a particular size. Note that the height
    * of the font is independent of the particular glyphs being displayed, so
    * this method does not accept a `text` param, like
-   * [[PDFStandardFontFactory.widthOfTextAtSize]] does.
+   * [[PDFEmbeddedFontFactory.widthOfTextAtSize]] does.
    */
   heightOfFontAtSize = (size: number) => {
     const { ascent, descent, bbox } = this.font;
@@ -162,6 +162,19 @@ class PDFEmbeddedFontFactory {
     return ((yTop - yBottom) / 1000) * size;
   };
 
+  /**
+   * Measures the size of this font at a particular height. Note that the size
+   * of the font is independent of the particular glyphs being displayed, so
+   * this method does not accept a `text` param, like
+   * [[PDFEmbeddedFontFactory.widthOfTextAtSize]] does.
+   */
+  sizeOfFontAtHeight = (height: number): number => {
+    const { ascent, descent, bbox } = this.font;
+    const yTop = (ascent || bbox.maxY) * this.scale;
+    const yBottom = (descent || bbox.minY) * this.scale;
+    return (1000 * height) / (yTop - yBottom);
+  };
+
   private embedFontDictionaryIn = (pdfDoc: PDFDocument, fontName: string) => {
     const cidFontDictRef = this.embedCIDFontDictionaryIn(pdfDoc, fontName);
     const unicodeCMap = this.embedUnicodeCmapIn(pdfDoc);

src/core/pdf-structures/factories/PDFStandardFontFactory.ts

@@ -139,6 +139,19 @@ class PDFStandardFontFactory {
     return ((yTop - yBottom) / 1000) * size;
   };
 
+  /**
+   * Measures the size of this font at a particular height. Note that the size
+   * of the font is independent of the particular glyphs being displayed, so
+   * this method does not accept a `text` param, like
+   * [[PDFStandardFontFactory.widthOfTextAtSize]] does.
+   */
+  sizeOfFontAtHeight = (height: number): number => {
+    const { Ascender, Descender, FontBBox } = this.font;
+    const yTop = Ascender || FontBBox[3];
+    const yBottom = Descender || FontBBox[1];
+    return (1000 * height) / (yTop - yBottom);
+  };
+
   // We'll default to 250 if our font metrics don't specify a width
   private widthOfGlyph = (glyphName: string) =>
     this.font.getWidthOfGlyph(glyphName) || 250;