FontForge Metrics View Purpose and Usage

The Metrics View window in FontForge is a dedicated workspace designed for adjusting horizontal spacing, setting side bearings, and fine-tuning kerning pairs. This guide explains the primary purpose of the Metrics View, how it allows type designers to evaluate text strings in real time, and the essential tools it provides to achieve proper typographic rhythm and spacing consistency across a font family.

Understanding the Purpose of the Metrics View

In digital typography, the shape of a glyph is only half of the design; the empty space around the glyph is equally critical for legibility. While the Glyph Outline window focuses on drawing vector contours, the Metrics View allows designers to manage the white space between and around characters.

The primary goal of the Metrics View is to ensure that letters flow naturally when assembled into words and sentences, preventing characters from colliding or appearing disjointed.

Core Functions of the Metrics View

1. Adjusting Advance Width and Side Bearings

Every glyph sits within an invisible bounding box defined by its advance width and two side bearings:

  • Left Side Bearing (LSB): The distance between the origin (zero point) and the leftmost edge of the glyph contour.
  • Right Side Bearing (RSB): The distance between the rightmost edge of the glyph contour and the character's advance width.
  • Advance Width: The total horizontal distance the text cursor advances after the character is placed.

In the Metrics View, designers can drag metric lines graphically or enter exact numerical values in the table below the viewport. This makes it easy to standardize spacing across visually similar characters, such as aligning the left side bearing of "H", "B", "D", and "P".

2. Fine-Tuning Kerning Pairs

Kerning refers to intentional spacing adjustments between specific pairs of glyphs where standard side bearings leave awkward visual gaps (such as "AV", "To", or "Wa").

Within the Metrics View, users can:

  • Click and drag the space between any two adjacent characters to manually adjust the kerning value.
  • Create and manage pair-to-pair kerning or class-based kerning.
  • Test kerning across upper- and lowercase transitions, punctuation, and numerals.

3. Real-Time Text Evaluation

The Metrics View functions as an interactive text string viewer. Designers can enter custom words, pangrams, or strings of text directly into the display buffer. This functionality allows for:

  • Proofing rhythm, letter spacing, and balance across complex combinations.
  • Checking diacritics and accent positioning alongside base letters.
  • Evaluating how optical weight distributions look at different horizontal densities.

4. Vertical Metrics Support

For fonts designed to support scripts with vertical text orientation (such as East Asian scripts), the Metrics View can be toggled to display top and bottom side bearings and vertical advance values, allowing precise control over vertical text flow.