Merges multiple fonts and generates a multi-channel signed-distance-field font bitmap.

readme.md

You must have both FontForge and msdf-atlas-gen installed and on your PATH (the letter may also just be in the current working directory).

To use it: fontforge -lang=py -script generator.py BASEFONT FONT...

• BASEFONT should be a regular font, like Arial, Roboto, Courier New, or anything you might get from https://www.fonts101.com/
• FONT can be any kind of font, including icon-fonts, emoji-fonts (without colors!) and other symbol-sets.

To render text with the resulting MSDF, you can use this shader:

in vec2 texCoord;
out vec4 color;
uniform sampler2D msdf;
uniform vec4 bgColor;
uniform vec4 fgColor;
uniform float pxRange = 4; // set to distance field's pixel range

float screenPxRange() {
    vec2 unitRange = vec2(pxRange)/vec2(textureSize(msdf, 0));
    vec2 screenTexSize = vec2(1.0)/fwidth(texCoord);
    return max(0.5*dot(unitRange, screenTexSize), 1.0);
}
float median(float r, float g, float b) {
    return max(min(r, g), min(max(r, g), b));
}

void main() {
    vec3 msd = texture(msdf, texCoord).rgb;
    float sd = median(msd.r, msd.g, msd.b);
    float screenPxDistance = screenPxRange()*(sd - 0.5);
    float opacity = clamp(screenPxDistance + 0.5, 0.0, 1.0);
    color = mix(bgColor, fgColor, opacity);
}

Building the text geometry is a bit more involved, but uses the same principles as any other bitmap font, and thus left as an exercise to the reader.

generator.py

import re
import sys
import fontforge

print(f"MSDF Multi-Font Merger & Generator! Python {sys.version}")

merged = None
#merged = fontforge.font()
#merged.fontname = "merged"
#merged.encoding = "UnicodeFull"
#merged.em = 4096

glyph_list_path = "merged.txt"
glyph_list_file = open(glyph_list_path, "w")

s = ''.join(chr(c) for c in range(sys.maxunicode+1))
ws = ''.join(re.findall(r'\s', s))

font_paths = sys.argv[1:]
for font_path in font_paths:
	print(f"Loading {font_path}")
	font = fontforge.open(font_path)
	
	if font.encoding != "UnicodeFull":
		font.encoding = "UnicodeFull"
	
	print(f"Selecting {font_path}")
	available = 0
	if merged is not None:
		merged.selection.none()
	for glyph in font.glyphs("encoding"):
		if glyph.unicode == -1 or chr(glyph.unicode) in ws:
			continue
		
		glyph_list_file.write(f"{glyph.unicode}\n")
		available += 1
		
		#print(f"- {glyph}")
		font.selection.select(("more",None), glyph)
		
		if merged is not None:
			merged.selection.select(("more",None), glyph)
	pass
	
	selected = sum(1 for _ in font.selection)
	print(f"Selected {selected} out of {available} glyphs")
	
	print(f"Rescaling {font_path}")
	font.em = 4096 # rescale
	
	if merged is None:
		merged = font
	else:
		print(f"Merging {font_path}")
		font.copy()
		merged.paste()
pass

glyph_list_file.close()

print(f"Rebuilding Data")
merged.buildOrReplaceAALTFeatures()

#print(f"Validating")
#v = merged.validate(1)

print(f"Saving")
merged.fontname = "merged"
merged_ttf = merged.fontname + ".ttf"
merged.generate(
	merged_ttf, 
	flags = ("opentype", "dummy-dsig")
)

print(f"Locating 'msdf-atlas-gen'")
import shutil
msdfgen = shutil.which("msdf-atlas-gen")

print(f"Found 'msdf-atlas-gen' at {msdfgen}; executing...")
merged_png = merged.fontname + ".png"
merged_json = merged.fontname + ".json"
merged_csv = merged.fontname + ".csv"

import subprocess
subprocess.run([
	msdfgen,
	"-font", merged_ttf,
	"-charset", glyph_list_path,
	"-type", "mtsdf",
	"-imageout", merged_png,
	"-json", merged_json,
	"-csv", merged_csv,
	"-potr",
	"-pxrange", "4",
	"-size","48",
	"-minsize", "32",
	"-threads", "0"
], stdout=sys.stdout, stderr=sys.stderr)

print(f"Done!")