Font size rendering

[rjopek]

Hi,

First of all, I would like to sincerely thank the creators and supporters of the stb libraries for their fantastic work. I am a user of the stb_truetype library and have encountered a problem that I hope someone could help me with.

My issue concerns font rendering. I am using the "Courier New" font with a size of 12, but I've noticed that the rendered font in my application is significantly smaller compared to the same font size in other applications. To achieve a comparable visual size, I have to set the font size to 18 in my code.

Could someone please explain what I might be doing wrong, or suggest how I can improve the scaling of the font to match the expected sizes?

https://github.com/dev-harbour/hbgl/blob/main/src/truetype.c#L193

Thank you in advance for any help and suggestions.

[nothings]

As is documented, BakeFontBitmap takes the desired height of the text in pixels, not the classic "point size". If you want to use point size with stbtt font baking, switch to the advance font baking API which begins with stbtt_PackBegin and pass in the desired size as STBTT_POINT_SIZE(12).

[rjopek]

Alternatively, can keep the current code, but it would be necessary to convert the font size from points to pixels using a factor of 1.3333, which comes from converting 1 point (1/72 of an inch) to the standard 96 DPI of a screen. For example, 12 points is approximately 16 pixels (12 * 1.3333 ≈ 16).

[nothings]

There isn't actually a guaranteed simple ratio, as the two are computed via different mechanisms.

stbtt_ScaleForPixelHeight (used by BakeFontBitmap) looks at the (reported) font bounding box info and is guaranteed to produce reasonable results (as long as the bounding box info is correct, which it basically always is).

stbtt_ScaleForMappingEmToPixels (used for STBTT_POINT_SIZE) uses the reported "unitsPerEm" field of the font, which I found through experience was sometimes wildly wrong in amateur fonts. This can be seen in programs that use traditional font units; as you cycle through fonts in photoshop, you may see the text size change radically if you've installed non-standard fonts.

Since the purpose of stb_truetype was to support game developers (who often use oddball fonts), there didn't seem much point in supporting the traditional mechanism that produced random sizes; it was only added later.