macOS: Fix some combining characters not being rendered

Use Harfbuzz for positioning instead of Core Text as Core Text doesn't
position combining chars correctly anymore. This may mean we need to
redo the cell metrics calculation as well, we will see. Core Text is
still used for rendering but at positions specified by Harfbuzz.

Fixes #6898

docs/changelog.rst

@@ -57,6 +57,8 @@ Detailed list of changes
 - Wayland: Fix a regression in the previous release that broke copying to clipboard under wl-roots based compositors in some circumstances
   (:iss:`6890`)
 
+- macOS: Fix some combining characters not being rendered (:iss:`6898`)
+
 
 0.31.0 [2023-11-08]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

kitty/core_text.m

@@ -319,6 +319,9 @@
     if (!self->hb_font) {
         self->hb_font = hb_coretext_font_create(self->ct_font);
         if (!self->hb_font) fatal("Failed to create hb_font");
+        // dunno if we need this, harfbuzz docs say it is used by CoreText
+        // for optical sizing which changes the look of glyphs at small and large sizes
+        hb_font_set_ptem(self->hb_font, self->scaled_point_sz);
         hb_ot_font_set_funcs(self->hb_font);
     }
     return self->hb_font;
@@ -421,13 +424,12 @@
     CGGlyph *glyphs;
     CGRect *boxes;
     CGPoint *positions;
-    CGSize *advances;
 };
 static struct RenderBuffers buffers = {0};
 
 static void
 finalize(void) {
-    free(buffers.render_buf); free(buffers.glyphs); free(buffers.boxes); free(buffers.positions); free(buffers.advances);
+    free(buffers.render_buf); free(buffers.glyphs); free(buffers.boxes); free(buffers.positions);
     memset(&buffers, 0, sizeof(struct RenderBuffers));
     if (all_fonts_collection_data) CFRelease(all_fonts_collection_data);
     if (window_title_font) CFRelease(window_title_font);
@@ -471,11 +473,10 @@
     }
     if (buffers.sz < num_glyphs) {
         buffers.sz = MAX(128, num_glyphs * 2);
-        buffers.advances = calloc(sizeof(buffers.advances[0]), buffers.sz);
         buffers.boxes = calloc(sizeof(buffers.boxes[0]), buffers.sz);
         buffers.glyphs = calloc(sizeof(buffers.glyphs[0]), buffers.sz);
         buffers.positions = calloc(sizeof(buffers.positions[0]), buffers.sz);
-        if (!buffers.advances || !buffers.boxes || !buffers.glyphs || !buffers.positions) fatal("Out of memory");
+        if (!buffers.boxes || !buffers.glyphs || !buffers.positions) fatal("Out of memory");
     }
 }
 
@@ -631,13 +632,15 @@
             return ret;
         }
     }
-    (void)units_per_em;
     CGFloat x = 0, y = 0;
-    CTFontGetAdvancesForGlyphs(ct_font, kCTFontOrientationDefault, buffers.glyphs, buffers.advances, num_glyphs);
+    CGFloat scale = CTFontGetSize(ct_font) / units_per_em;
     for (unsigned i=0; i < num_glyphs; i++) {
-        buffers.positions[i].x = x; buffers.positions[i].y = y;
-        if (debug_rendering) printf("x=%f origin=%f width=%f advance=%f\n", x, buffers.boxes[i].origin.x, buffers.boxes[i].size.width, buffers.advances[i].width);
-        x += buffers.advances[i].width; y += buffers.advances[i].height;
+        buffers.positions[i].x = x + hb_positions[i].x_offset * scale; buffers.positions[i].y = y + hb_positions[i].y_offset * scale;
+        if (debug_rendering) printf("x=%f y=%f origin=%f width=%f x_advance=%f x_offset=%f y_advance=%f y_offset=%f\n",
+                buffers.positions[i].x, buffers.positions[i].y, buffers.boxes[i].origin.x, buffers.boxes[i].size.width,
+                hb_positions[i].x_advance * scale, hb_positions[i].x_offset * scale,
+                hb_positions[i].y_advance * scale, hb_positions[i].y_offset * scale);
+        x += hb_positions[i].x_advance * scale; y += hb_positions[i].y_advance * scale;
     }
     if (*was_colored) {
         render_color_glyph(ct_font, (uint8_t*)canvas, info[0].codepoint, cell_width * num_cells, cell_height, baseline);
@@ -692,8 +695,8 @@
 static PyObject *
 repr(CTFace *self) {
     char buf[1024] = {0};
-    snprintf(buf, sizeof(buf)/sizeof(buf[0]), "ascent=%.1f, descent=%.1f, leading=%.1f, point_sz=%.1f, scaled_point_sz=%.1f, underline_position=%.1f underline_thickness=%.1f",
-        (self->ascent), (self->descent), (self->leading), (self->point_sz), (self->scaled_point_sz), (self->underline_position), (self->underline_thickness));
+    snprintf(buf, sizeof(buf)/sizeof(buf[0]), "ascent=%.1f, descent=%.1f, leading=%.1f, scaled_point_sz=%.1f, underline_position=%.1f underline_thickness=%.1f",
+        (self->ascent), (self->descent), (self->leading), (self->scaled_point_sz), (self->underline_position), (self->underline_thickness));
     return PyUnicode_FromFormat(
         "Face(family=%U, full_name=%U, postscript_name=%U, path=%U, units_per_em=%u, %s)",
         self->family_name, self->full_name, self->postscript_name, self->path, self->units_per_em, buf
@@ -709,7 +712,6 @@
 static PyMemberDef members[] = {
 #define MEM(name, type) {#name, type, offsetof(CTFace, name), READONLY, #name}
     MEM(units_per_em, T_UINT),
-    MEM(point_sz, T_FLOAT),
     MEM(scaled_point_sz, T_FLOAT),
     MEM(ascent, T_FLOAT),
     MEM(descent, T_FLOAT),