Why does the command line interface's font input mode convert font units to pixels by dividing by 64?

[TJYSunset]

Sorry if this have already been mentioned before.

I'm no expert in typography, but if I'm not mistaken -

• The call to FT_Load_Glyph set the FT_LOAD_NO_SCALE flag, so its return value is expressed in the exact font units, not 26.6 fractional pixels;
• The typical font unit to em ratio is either 1000:1, 1024:1 or 2048:1, and is retrievable as FT_FaceRec.units_per_em;
• 1 em equals the currently specified pt size;
• Pixels per pt depends on the DPI, which is typically 72, 96 or 300+;
• None of the above conversions involve a multiplier/divisor of 64.

To be clear, I don't think this behavior needs "fixing" (changing the behavior will only break existing code). It just needs clear documentation in the README.

[Chlumsky]

Can you point out the specific division that you think is incorrect? I believe it is done to convert FreeType's fixed point number format (integer whose most significant 26 bits are the whole part and least significant 6 bits are the fractional part) to floating point.

[TJYSunset]

I believe it's in ftPoint2(), which is called by all the FT_Outline_Decompose callback functions.

According to FreeType docs, FT_Pos (used in FT_Vector) can either be 26.6 pixels or 1:1 font units, which seems to actually be font units in this case.

I tested rendering Fira Sans Bold's capital M with

msdfgen msdf -font .\FiraSans-Bold.otf "'M'" -scale 64 -size 1000 1000 -pxrange 4 -testrender test.png 1000 1000

And the output test render is exactly 720px wide, matching FontForge's telling me this glyph is 720 font units wide.

test.png:

FontForge:

[Chlumsky]

Alright, in that case, I guess it is wrong.

[Chlumsky]

Fixed in bc9f02e156115860e28094565c57d383ab03b761, hopefully with full backwards compatibility.

Use:

• -noemnormalize / FONT_SCALING_NONE to switch to the correct native font coordinates,
• -emnormalize / FONT_SCALING_EM_NORMALIZED to switch to coordinates normalized to 1 em, or
• -legacyfontscaling / FONT_SCALING_LEGACY to keep old behavior and make sure it will not change.

If you do not specify any of the above, you will get a warning in the console version, but for now, the old behavior will be kept.