Why can't I combine different weights of a TTF font?

You might be wondering, "Why can't I combine different weights of a TTF font?". The answer lies in how fonts are designed and managed by operating systems and rendering engines.

Here's a breakdown of the key reasons:

1. Fonts as Separate Files:

- Different font weights (e.g., Regular, Bold, Italic) are typically provided as separate font files. Each file contains the glyph shapes and metrics specifically designed for that weight. Think of 'Roboto-Regular.ttf' and 'Roboto-Bold.ttf' as completely different entities.

2. Font Linking and Family Names:

- Modern operating systems and browsers rely on the font's family name and internal metadata to link different weights together. This linking is facilitated by the CSS font-family property. For example:

font-family: 'Roboto', sans-serif;
font-weight: bold; / Tells the browser to use the 'Bold' variant if available /

- In this setup, the browser automatically picks the appropriate font file (e.g., 'Roboto-Bold.ttf') based on the specified font-weight.

3. Technical Limitations of Combining Weights:

- TTF (TrueType Font) files contain precise instructions on how each character glyph should be rendered. Merging weights directly into one file would create conflicts and rendering errors. The glyph shapes and spacing are different for each weight; they are not simply scaled versions of the regular weight.

4. Font Synthesis (Fake Bold/Italic):

- Browsers can attempt to synthesize bold or italic versions of fonts if the specific weight isn't available. However, this often results in poor quality and is generally discouraged. It's better to provide the actual font weight files.

5. OpenType (OTF) and Variable Fonts:

- While TTF has limitations, OpenType (OTF) fonts offer more flexibility. And, more recently, variable fonts (a type of OTF) have emerged, allowing multiple weights and styles to be contained within a single font file. However, these still require proper CSS and font declarations to leverage the different weights.

In summary, TTF fonts typically require separate files for each weight due to the way they are designed and how operating systems handle font rendering. Using CSS's font-family and font-weight properties is the correct way to specify different weights, allowing the browser to choose the appropriate font file.

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