sometimes when I am bored I look at the kitty terminal's source code. it's so good!

void
shaped_run_put(
    SHAPED_RUN_MAP_HANDLE map,
    const CPUCell *cells,
    index_type num_cells,
    const TextCache *tc,
    bool disable_ligature,
    bool force_ltr,
    uint8_t scale,
    uint8_t subscale,
    const hb_glyph_info_t *info,
    const hb_glyph_position_t *positions,
    unsigned num_glyphs,
    const ShapeGroup *groups,
    unsigned num_groups) {
    HashTable *ht = (HashTable *)map;
    if (!ht) return;
    if (shaped_run_too_long(num_cells)) return;
    if ((num_glyphs && (!info || !positions)) || (num_groups && !groups)) return;
    if (!fill_key(ht, cells, num_cells, tc, disable_ligature, force_ltr, scale, subscale)) return;
#define scratch ht->scratch.key
    if (!vt_is_end(vt_get(&ht->table, scratch))) return;
    if (shaped_run_at_cap(ht)) shaped_run_drop(ht);
    ShapedRunKey *key = Key_get(&ht->keys, sizeof(ShapedRunKey) + scratch->keysz_in_bytes);
    if (!key) return;
    memcpy(key, scratch, sizeof(scratch[0]) + scratch->keysz_in_bytes);
    ShapedRunValue *val = Val_get(&ht->vals, val_size(num_glyphs, num_groups));
    if (!val) return;
    val->num_glyphs = num_glyphs;
    val->num_groups = num_groups;
    if (num_glyphs) {
        memcpy(val_info(val), info, num_glyphs * sizeof(info[0]));
        memcpy(val_positions(val), positions, num_glyphs * sizeof(positions[0]));
    }
    if (num_groups) memcpy(val_groups(val), groups, num_groups * sizeof(groups[0]));
    if (vt_is_end(vt_insert(&ht->table, key, val))) return;
#undef scratch
}

put a #define in the middle of a function body for some reason! why not! you are allowed to do anything! the buttons on the keyboard are there to be pressed! press them however you want!