Setting font features and font variations. (#503) #506

Martin-Eriksson · 2025-02-06T06:25:56Z

Closes #503.

I've got some comments in there with questions about how to do certain things.

I had thought I could use hb_font_set_variations and it would be super easy,
barely an inconvenience, to support setting variations but it does nothing at all.
Instead I had to use FreeType directly, which took me a while to figure out how
to do. Do you think hb_font_set_variations is supposed to work? Or is it correct
that it does nothing when using FreeType, perhaps?

font->enable_kerning is not used at all anymore, TTF_SetFontFeatures and TTF_SetFontKerning
are completely independent. It ignores the font->enable_kerning value
if TTF_SetFontFeatures has been called with a non-null string. If TTF_SetFontFeatures
is called later with a null string, it starts using the font->enable_kerning value again.
Combining them is a bit complicated if we want to avoid doing more work in CollectGlyphsFromFont().

I've tried to run address sanitizer on the code but I haven't got it working yet.
It reports nothing even though I've commented out calls to free.

Until I've figured out how to get ASan working, and if hb_font_set_variations is supposed to work, I'm keeping this as
a draft PR

slouken · 2025-02-17T17:37:03Z

@Martin-Eriksson, I'd like to wrap up an SDL_ttf release, what's the status of this PR? We can definitely add these functions later, but if you'd like to get them in, I'm fine with that.

RobertSundling · 2025-03-11T23:44:04Z

I noticed some compiler warnings when testing this PR with GCC. I've fixed these warnings in my fork at:
https://github.com/RobertSundling/SDL_ttf/tree/fix-pr506-compiler-warnings

Feel free to incorporate these fixes into this PR if you find them useful.

mcendu

Are you still working on this? If not, can I take this over?

Also what were you doing when ASan threw the error, and what did ASan print?

mcendu · 2025-11-25T01:59:12Z

src/SDL_ttf.c

+//naming? it's not from FreeType so maybe FT_ is inappropriate?
+typedef struct FT_Variations { 
+    int len;
+    FT_ULong *tags;
+    FT_Fixed *defaults;
+    FT_Fixed *coords;
+} FT_Variations;


Just name it variations as this is an internal struct.

mcendu · 2025-11-25T02:08:30Z

src/SDL_ttf.c

+#if TTF_USE_HARFBUZZ
+    return font->features;
+#else
+    (void) features;


This line is unnecessary.

mcendu · 2025-11-25T02:21:14Z

src/SDL_ttf.c

+        // The documentation (https://freetype.org/freetype2/docs/reference/ft2-multiple_masters.html#ft_mm_var)
+        // talks about named styles, like how 'bold' could be defined as [Weight=1.5,Width=1.1].
+        // is that something we should care about? I don't know if HarfBuzz even parses that.


There is hb_set_var_named_instance() and hb_font_get_var_named_instance() for dealing with these. If you want the user to specify names instead of numbers, you can refer to hb-ot-var.

Like HarfBuzz and FreeType, you should probably add a separate set of functions for dealing with named instances.

mcendu · 2025-11-25T02:23:30Z

src/SDL_ttf.c

+#if 0
+        //! hb_font_set_variations does nothing
+        //! hb_font_set_variation doesn't work either
+        // is it supposed to work? Is it a bug in HarfBuzz or does it not work
+        // because we're using FreeType?
+        hb_font_set_variations(font->hb_font, font->variations, font->variations_len);
+#else
+        // should we care if this returns an error? what should we do in that case?
+        FT_Set_Var_Design_Coordinates(font->face, font->ft_variations.len, font->ft_variations.coords);
+#endif


Try calling hb_ft_hb_font_changed() after hb_font_set_variations()?

While you no longer need to call it in HarfBuzz 11.0.0 or later, not all distributions ship this new a HarfBuzz.

Suggested change

#if 0

//! hb_font_set_variations does nothing

//! hb_font_set_variation doesn't work either

// is it supposed to work? Is it a bug in HarfBuzz or does it not work

// because we're using FreeType?

hb_font_set_variations(font->hb_font, font->variations, font->variations_len);

#else

// should we care if this returns an error? what should we do in that case?

FT_Set_Var_Design_Coordinates(font->face, font->ft_variations.len, font->ft_variations.coords);

#endif

hb_font_set_variations(font->hb_font, font->variations, font->variations_len);

hb_ft_hb_font_changed(font->hb_font);

This commit adds the functionality to directly set font variation settings and font features. The work directly builds upon a prior attempt from libsdl-org#506. Instead of parsing a single string, the API is changed to handle arrays for easier maintenance. This also allows the font variation to be set without requiring HarfBuzz. Fixes: libsdl-org#503 Closes: libsdl-org#506 Co-authored-by: Martin Eriksson <[email protected]> Co-authored-by: Robert Sundling <[email protected]> Signed-off-by: Du Yijie <[email protected]>

This commit adds the functionality to directly set font variation settings and font features. The work directly builds upon a prior attempt from libsdl-org#506. Instead of parsing a single string, the API is changed to handle arrays for easier maintenance. This allows easier maintenance, and also allows font variations to be set without requiring HarfBuzz as in the prior attempt. Fixes: libsdl-org#503 Closes: libsdl-org#506 Co-authored-by: Martin Eriksson <[email protected]> Co-authored-by: Robert Sundling <[email protected]> Signed-off-by: Du Yijie <[email protected]>

This commit adds the functionality to directly set font variation settings. The work directly builds upon a prior attempt from libsdl-org#506. Instead of parsing a single string, the API is changed to expect an array of variation settings, in the same format expected by the HarfBuzz function hb_font_set_variations(). This allows the font variation to be set even when HarfBuzz is not used. Link: libsdl-org#503 Link: libsdl-org#506 Co-authored-by: Martin Eriksson <[email protected]> Co-authored-by: Robert Sundling <[email protected]> Signed-off-by: Du Yijie <[email protected]>

This commit adds the functionality to directly set font features. The work directly builds upon a prior attempt from libsdl-org#506. Instead of parsing a single string, the API is changed to expect an array of strings. OpenType features can be applied not only to everything using the font, but also to only a part of some text. This commit does not address this. Link: libsdl-org#503 Link: libsdl-org#506 Co-authored-by: Martin Eriksson <[email protected]> Co-authored-by: Robert Sundling <[email protected]> Signed-off-by: Du Yijie <[email protected]>

This commit adds the functionality to directly set font variation settings. The work directly builds upon a prior attempt from libsdl-org#506. Instead of parsing a single string, the API is changed to expect an array of variation settings, in the same format expected by the HarfBuzz function hb_font_set_variations(). This allows the font variation to be set even when HarfBuzz is not used. Link: libsdl-org#503 Link: libsdl-org#506 Co-authored-by: Martin Eriksson <[email protected]> Co-authored-by: Robert Sundling <[email protected]> Signed-off-by: Du Yijie <[email protected]>

This commit adds the functionality to directly set font features. The work directly builds upon a prior attempt from libsdl-org#506. Instead of parsing a single string, the API is changed to expect an array of features to apply globally, similar to the font variation support implementation. The option to apply a feature to a specific part of every text using the font is no longer present. OpenType features can be applied not only to everything using the font, but also to only a part of some text. This commit does not address this. Link: libsdl-org#503 Link: libsdl-org#506 Co-authored-by: Martin Eriksson <[email protected]> Co-authored-by: Robert Sundling <[email protected]> Signed-off-by: Du Yijie <[email protected]>

Implemented setting font features and font variations. (libsdl-org#503)

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Martin-Eriksson changed the title ~~Implemented setting font features and font variations. (#503)~~ Setting font features and font variations. (#503) Feb 6, 2025

RobertSundling added a commit to RobertSundling/SDL_ttf that referenced this pull request Mar 11, 2025

Fix compiler warnings in PR libsdl-org#506

2ad1ba4

TriangulumDesire mentioned this pull request Mar 18, 2025

Add font weight functionality #531

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TriangulumDesire mentioned this pull request Apr 1, 2025

[Feature request] Retrieving the weight of a font. #527

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mcendu suggested changes Nov 25, 2025

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mcendu mentioned this pull request Nov 27, 2025

Add basic support for font variations and features #601

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