Fonts: optional ImFont::KerningFn pair-adjust hook - #9516
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RenderText and CalcTextSize apply extra advance when set. NULL stays the current advance-only path so default text cost is unchanged. Lets hosts supply TTF kern or GPOS without baking pairs into the atlas.
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Summary
ImFont::KerningFn/KerningUserData: optional extra advance (pixels atsize) between consecutive codepoints.RenderTextandImFontCalcTextSizeExso layout matches draw.NULLkeeps the current advance-only path (one null check per glyph). No atlas / loader changes.Why
ImGui places glyphs by
AdvanceXonly. Hosts that already have pair data (legacykern, HarfBuzz GPOS, or a custom table) cannot feed it into chrome/ImGui::Textwithout wrapping every call. This hook is the smallest seam: the atlas stays a glyph cache; the host owns shaping.Omar noted in #618 that kerning would be nice as an optional per-font path because text-size calc is a bottleneck. This is that option: default cost is unchanged.
Word-wrap (
CalcWordWrapPosition) is not adjusted yet; wrap points can be off by the pair extras on a line. Happy to add that if this shape is acceptable.Test plan
KerningFn == NULL): demo / examples look identical.A+V;ImGui::Text(AV)andCalcTextSize(AV)both pick it up.