I am trying to create a custom ttf file using font forge. The purpose of building a single custom ttf file is to use all alpha-numeric characters (a-zA-Z0-9) of the 3 fonts as 1 font file. . The fonts I selected are sourceserif_pro regular, heuristica regular, and tex gyre regular. My plan is to combine all three font glyphs into one TTF using zero width non-joiners. I have created a custom ttf file keeping sourceserif as base ttf file and added entries for heuristica glyphs with 1 zero width non joiner,tex gyre glyphs with 2 non joiners. em size of custom ttf file 1024. When rendered in HTML using the custom ttf, there is a height difference between the letters in the Tex Gyre font alone (font size 21 onwards). I have attached the custom ttf and sample images to highlight the height difference.
I have experimented with the following:
Tried changing the em sizes in powers of 2 eg. 1024,2048.
The same ascent and decent value that was mentioned in the General tab of FontForge was transferred to the Metrics tab of FontForge.
Since there is no issue with heuristic glyphs with 1 non-joiner (odd number of non-joiners), I tried adding 3 non-joiners to Tex Gyre glyphs. The aforementioned methods have not helped me resolve the problemimage for reference custom ttf file created