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Add TTF_GetFontBBox() which returns font's extremum bounding box #538

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Add TTF_GetFontBBox() which returns font's extremum bounding box #538

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21 changes: 21 additions & 0 deletions SDL_ttf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3040,6 +3040,27 @@ void TTF_SetFontKerning(TTF_Font *font, int allowed)
#endif
}

void TTF_GetFontBBox(const TTF_Font *font, int *minx, int *maxx, int *miny, int *maxy)
{
if (!font || !font->face) {
return;
}
/* Recalculate FT_Face's bbox from font units to pixels */
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@slouken slouken Mar 28, 2025

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You should make sure the font is valid, see the other API functions for examples.

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@ivan-mogilko ivan-mogilko Mar 29, 2025 •
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Added a font pointer check. By the way, I noticed that not all functions have this check, only some do.

const FT_Face face = font->face;
if (minx) {
*minx = FT_MulFix(FT_DivFix(face->bbox.xMin, face->units_per_EM), face->size->metrics.x_ppem);
}
if (maxx) {
*maxx = FT_MulFix(FT_DivFix(face->bbox.xMax, face->units_per_EM), face->size->metrics.x_ppem);
}
if (miny) {
*miny = FT_MulFix(FT_DivFix(face->bbox.yMin, face->units_per_EM), face->size->metrics.y_ppem);
}
if (maxy) {
*maxy = FT_MulFix(FT_DivFix(face->bbox.yMax, face->units_per_EM), face->size->metrics.y_ppem);
}
}

long TTF_FontFaces(const TTF_Font *font)
{
return font->face->num_faces;
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16 changes: 16 additions & 0 deletions SDL_ttf.h
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Expand Up @@ -678,6 +678,22 @@ extern DECLSPEC int SDLCALL TTF_GetFontKerning(const TTF_Font *font);
*/
extern DECLSPEC void SDLCALL TTF_SetFontKerning(TTF_Font *font, int allowed);

/**
* Query the font bounding box.
*
* The bounding box defines bounds large enough to contain any glyph from
* the font. It is expressed in pixel offsets from glyph's origin (0,0),
* with Y axis pointing upwards. Thus ymax offset may be seen as the
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@slouken slouken Mar 28, 2025

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This is the opposite of how coordinates are usually done in SDL. Can you double check the other SDL_ttf APIs and see if that's consistent here?

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@ivan-mogilko ivan-mogilko Mar 28, 2025 •
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By "opposite", are you referring to Y axis? I know that SDL has it downwards in e.g. drawing, the upwards Y is FT specific, it has ascender as a positive offset and descender as a negative offset afaik.
But I will check what other functions are doing.

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@ivan-mogilko ivan-mogilko Mar 29, 2025 •
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I can confirm that TTF_FontAscent and TTF_FontDescent functions return these offsets in a similar style: ascent is normally a positive value and descent is a negative value, as if Y axis is pointing up. For properly done fonts their return values also match miny and maxy values returned from TTF_GetFontBBox. (Their values differ for the fonts which have incorrect metrics information in them.)

EDIT: Also checked TTF_GlyphMetrics, and its return values seem fully consistent as well.

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@ivan-mogilko ivan-mogilko Mar 29, 2025

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By the way, since there's a TTF_GlyphMetrics function, do you think that TTF_GetFontBBox is a okay name, or should I rename to something more consistent with "GlyphMetrics"? Because the meaning of BBox is essentially "max known glyph metrics".

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@slouken slouken Mar 29, 2025

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Okay, thanks for checking, that seems fine to me. I'm not sure on the name, let me think about it a bit. What's the use case for this function?

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@ivan-mogilko ivan-mogilko Mar 29, 2025

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What's the use case for this function?

In my case (mentioned in #536), there are fonts that have incorrect ascent/descent information for some reason (maybe because font's creator made a mistake), but there's still a way to tell how big their characters are using this bounding box info. This helps if we want to precalculate a necessary texture size before first render happened, for example.

* "maximum ascender" and ymin offset - as the "minimum descender".
*
* \param font the font to query.
*
* \since This function is available since SDL_ttf 2.26.0.
*/
extern DECLSPEC void SDLCALL TTF_GetFontBBox(const TTF_Font *font,
int *minx, int *maxx,
int *miny, int *maxy);

/**
* Query the number of faces of a font.
*
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