increase_line_height.py

import fontforge
import sys

def increase_line_spacing(input_font, output_font, increase_factor):
    font = fontforge.open(input_font)

    # Store the original values
    original_em = font.em
    original_ascent = font.ascent
    original_descent = font.descent

    # Calculate the additional line gap
    additional_line_gap = int(original_em * (increase_factor - 1))

    # Adjust the OS/2 metrics to increase line spacing
    font.os2_typoascent = original_ascent
    font.os2_typodescent = -original_descent
    font.os2_typolinegap = font.os2_typolinegap + additional_line_gap

    # Adjust win ascent and descent to accommodate the increased line spacing
    font.os2_winascent = original_ascent + (additional_line_gap // 2)
    font.os2_windescent = original_descent + (additional_line_gap // 2)

    # Ensure hhea table metrics are consistent
    font.hhea_ascent = font.os2_winascent
    font.hhea_descent = -font.os2_windescent
    font.hhea_linegap = 0

    # Generate the new font
    font.generate(output_font)
    print(f"New font saved as {output_font}")

if __name__ == "__main__":
    if len(sys.argv) != 4:
        print("Usage: fontforge -script script.py input_font.ttf output_font.ttf increase_factor")
        sys.exit(1)

    input_font = sys.argv[1]
    output_font = sys.argv[2]
    increase_factor = float(sys.argv[3])

    increase_line_spacing(input_font, output_font, increase_factor)