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Fix text kerning, HiDPI glyph padding, and invisible-glyph rasterization #511

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Merged
RandyGaul merged 3 commits into from
Jul 6, 2026
Merged

Fix text kerning, HiDPI glyph padding, and invisible-glyph rasterization #511

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272f0bc
Apply kerning to text layout cursor
pusewicz Jul 6, 2026
69c8109
Skip kerning for the first glyph
pusewicz Jul 6, 2026
1228f97
Fix HiDPI glyph padding and stop rasterizing invisible glyphs
pusewicz Jul 6, 2026
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69 changes: 53 additions & 16 deletions src/cute_draw.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1790,7 +1790,9 @@ CF_Result cf_make_font_from_memory(void* data, int size, const char* font_name)
stbtt_GetFontBoundingBox(&font->info, &x0, &y0, &x1, &y1);
font->width = x1 - x0;

// Build kerning table.
// Build the legacy kerning table, keyed by glyph index (as stb provides it). Used
// as a fallback in cf_font_get_kern for fonts whose GPOS table isn't in a layout
// stb's minimal parser understands, even though real kern data still exists here.
Array<stbtt_kerningentry> table_array;
int table_length = stbtt_GetKerningTableLength(&font->info);
table_array.ensure_capacity(table_length);
Expand Down Expand Up @@ -1966,7 +1968,12 @@ static void s_render(CF_Font* font, CF_Glyph* glyph, float font_size, int blur)
glyph->q0 = V2((float)x0, -(float)(y0 + h)) / pixel_scale; // Swapped y. Logical units.
glyph->q1 = V2((float)(x0 + w), -(float)y0) / pixel_scale; // Swapped y. Logical units.
glyph->xadvance = xadvance * scale / pixel_scale;
glyph->visible |= w > 0 && h > 0;
glyph->rendered = true;

// Glyphs with no ink (spaces, etc.) have nothing to rasterize -- layout metrics
// above are still valid and needed, but skip allocating a bitmap/atlas slot for
// them entirely, and skip drawing them (see `visible` check in s_draw_text).
if (!glyph->visible) return;

// Render glyph.
uint8_t* pixels_1bpp = (uint8_t*)CF_CALLOC(w * h);
Expand Down Expand Up @@ -2012,7 +2019,7 @@ CF_Glyph* cf_font_get_glyph(CF_Font* font, int code, float font_size, int blur)
glyph->index = glyph_index;
glyph->visible = stbtt_IsGlyphEmpty(&font->info, glyph_index) == 0;
}
if (glyph->image_id) return glyph;
if (glyph->rendered) return glyph;

// Render the glyph if it exists in the font, but is not yet rendered.
s_render(font, glyph, font_size, blur);
Expand All @@ -2021,10 +2028,22 @@ CF_Glyph* cf_font_get_glyph(CF_Font* font, int code, float font_size, int blur)

float cf_font_get_kern(CF_Font* font, float font_size, int code0, int code1)
{
uint64_t key = CF_KERN_KEY(code0, code1);
int* val = font->kerning.try_get(key);
if (!val) return 0;
return *val * stbtt_ScaleForPixelHeight(&font->info, font_size);
// Prefer GPOS -- stb's codepoint API converts to glyph indices internally and
// reads GPOS pair-adjustment tables, which is where most modern fonts keep
// kerning. But stb's GPOS parser only understands a narrow set of lookup
// formats: some fonts (e.g. this project's bundled Calibri) have a GPOS table
// stb can't read, yet still carry real data in the legacy `kern` table. Since
// stb only consults `kern` when there's no GPOS table at all, fall back to our
// own glyph-index lookup into `kerning` (built in cf_make_font_from_data) when
// the GPOS path comes up empty.
int advance = stbtt_GetCodepointKernAdvance(&font->info, code0, code1);
if (!advance) {
int g0 = stbtt_FindGlyphIndex(&font->info, code0);
int g1 = stbtt_FindGlyphIndex(&font->info, code1);
int* val = font->kerning.try_get(CF_KERN_KEY(g0, g1));
if (val) advance = *val;
}
return advance * stbtt_ScaleForPixelHeight(&font->info, font_size);
}

void cf_push_font(const char* font)
Expand Down Expand Up @@ -2204,6 +2223,10 @@ static const char* s_find_end_of_line(CF_Font* font, const char* text, float wra
const char* start_of_word = 0;
float word_w = 0;
int cp;
int cp_prev = 0;
// Mirrors the main render loop's hit_newline gating, so wrap points land where
// the kerned text will actually break.
bool at_line_start = true;

while (*text) {
const char* text_prev = text;
Expand All @@ -2214,22 +2237,25 @@ static const char* s_find_end_of_line(CF_Font* font, const char* text, float wra
x = 0;
word_w = 0;
start_of_word = 0;
at_line_start = true;
continue;
} else if (cp == '\r') {
continue;
} else {
float kern = at_line_start ? 0 : cf_font_get_kern(font, font_size, cp_prev, cp);
float advance = glyph->xadvance + kern;
if (s_is_space(cp)) {
x += word_w + glyph->xadvance;
x += word_w + advance;
word_w = 0;
start_of_word = 0;
} else {
if (!start_of_word) {
start_of_word = text_prev;
}
if (x + word_w + glyph->xadvance < wrap_width) {
word_w += glyph->xadvance;
if (x + word_w + advance < wrap_width) {
word_w += advance;
} else {
if (word_w + glyph->xadvance < wrap_width) {
if (word_w + advance < wrap_width) {
// Put entire word on the next line.
return start_of_word;
} else {
Expand All @@ -2238,6 +2264,8 @@ static const char* s_find_end_of_line(CF_Font* font, const char* text, float wra
}
}
}
cp_prev = cp;
at_line_start = false;
}
}

Expand Down Expand Up @@ -2766,6 +2794,13 @@ static v2 s_draw_text(const char* text, CF_V2 position, int text_length, bool re
continue;
}

// Advance the cursor by the pair kern so it accumulates across the line and is
// reflected in measurement + bounds, not just the visible glyph. Horizontal only;
// hit_newline guards against kerning across line breaks.
if (!vertical && !hit_newline && cp_prev) {
x += cf_font_get_kern(font, font_size, cp_prev, cp);
}

// Prepare a sprite struct for rendering.
float xadvance = glyph->xadvance;
if (render || markups) {
Expand All @@ -2777,11 +2812,13 @@ static v2 s_draw_text(const char* text, CF_V2 position, int text_length, bool re
s.geom.alpha = 1.0f;
CF_Color color = s_draw->colors.last();

uint64_t kern_key = CF_KERN_KEY(cp_prev, cp);
v2 kern = V2(cf_font_get_kern(font, font_size, cp_prev, cp), 0);
v2 pad = V2(1,1); // Account for 1-pixel padding in spritebatch.
v2 q0 = glyph->q0 + V2(x,y) + kern - pad;
v2 q1 = glyph->q1 + V2(x,y) + kern + pad;
// Account for spritebatch's 1-pixel atlas border. The border is 1 *device*
// pixel (glyph bitmaps are rasterized at pixel_scale resolution), but q0/q1
// are in logical units, so the pad must shrink by pixel_scale to match --
// otherwise on HiDPI the quad is stretched past the glyph's actual coverage.
v2 pad = V2(1,1) / app->pixel_scale;
v2 q0 = glyph->q0 + V2(x,y) - pad;
v2 q1 = glyph->q1 + V2(x,y) + pad;

// Apply any active custom text effects.
bool use_corner_colors = false;
Expand Down
1 change: 1 addition & 0 deletions src/internal/cute_font_internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@ struct CF_Glyph
int w, h;
float xadvance;
bool visible;
bool rendered; // Metrics (and, if visible, the atlas image) have been computed.
};

struct CF_Font
Expand Down
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