MeshCore-Solo/examples/companion_radio/ui-new/TabBar.h

#pragma once
// Shared circular tab-bar header, extracted after NearbyScreen and BotScreen
// had each independently grown byte-identical rendering code for the same
// "active tab centred as a pill, neighbours fan out either side and wrap
// around" layout (see NearbyScreen::drawFilterTabs / BotScreen::drawTabBar,
// pre-extraction). A third screen (AdminScreen) needing the same thing was
// the rule-of-three trigger to finally share it.
//
// Tab-switching itself (LEFT/RIGHT cycling the active index) is NOT part of
// this helper -- each screen's cycle has different side effects (refresh a
// list, reset a row selection, ...), so that one-liner stays inline per screen.

namespace tabbar {

// One tab: short label; the active one is an inverted pill (same look as a
// selected row) so it reads as "you are here" in the tab strip.
inline void drawPill(DisplayDriver& display, int x, int w, const char* label, bool active) {
  int lh = display.getLineHeight();
  if (active) {
    display.setColor(DisplayDriver::LIGHT);
    display.fillRect(x, 0, w, lh + 1);
    display.setColor(DisplayDriver::DARK);
  } else {
    display.setColor(DisplayDriver::LIGHT);
  }
  display.drawTextCentered(x + w / 2, 0, label);
  display.setColor(DisplayDriver::LIGHT);
}

// Truncate `label` to fit within `max_w` pixels of text (no padding). Similar
// intent to DisplayDriver::drawTextEllipsized (which can't be reused directly
// here: it draws immediately at a fixed x, but a tab pill needs the truncated
// width known *before* drawing, to size/centre the pill), but verifies the
// fit by re-measuring the actual "text..." candidate at each step, rather
// than estimating via a separately-measured ellipsis width -- font kerning
// between the last real glyph and the first dot can make a single-pass
// estimate overshoot by a px or two, which was enough to visibly spill the
// dots into whatever sits just past this tab (a neighbour, a reserved icon
// like the context-menu hint). Returns the resulting text's pixel width
// (always <= max_w, unless even a bare "..." doesn't fit); writes the
// (possibly truncated) text into `out`.
inline int ellipsize(DisplayDriver& display, const char* label, int max_w, char* out, size_t out_sz) {
  strncpy(out, label, out_sz - 1);
  out[out_sz - 1] = '\0';
  int w = display.getTextWidth(out);
  if (w <= max_w) return w;

  int len = (int)strlen(out);
  char trial[40];
  while (len > 0) {
    // Strip an orphaned UTF-8 lead byte before trying this length.
    while (len > 0 && ((uint8_t)out[len - 1] & 0xC0) == 0xC0) len--;
    if (len == 0) break;
    memcpy(trial, out, len);
    strcpy(trial + len, "...");
    if (display.getTextWidth(trial) <= max_w) {
      strncpy(out, trial, out_sz - 1);
      out[out_sz - 1] = '\0';
      return display.getTextWidth(out);
    }
    len--;
  }
  strncpy(out, "...", out_sz - 1);
  out[out_sz - 1] = '\0';
  return display.getTextWidth(out);
}

// Header as a circular tab bar: the active tab sits centred as a filled pill,
// neighbours fan out either side and wrap around. A neighbour that doesn't
// fully fit in the space remaining on its side is drawn truncated with an
// ellipsis instead of being skipped, so the immediate left/right tabs stay
// visible (just shortened) rather than vanishing on a narrow display or a
// long active label -- only once even an ellipsis wouldn't fit does that side
// stop. `right_reserve` keeps any trailing decoration the caller draws
// afterwards (a context-menu hint, a counter) clear of the rightmost tab.
// Also draws the header separator line.
inline void draw(DisplayDriver& display, const char* const* labels, int count, int active, int right_reserve = 0) {
  const int pad = 3, gap = 2;
  const int min_w = pad * 2 + 6;   // smallest pill worth drawing (padding + a couple px of text)
  char buf[24];

  int aw = display.getTextWidth(labels[active]) + pad * 2;
  int ax = display.width() / 2 - aw / 2;
  drawPill(display, ax, aw, labels[active], true);

  int lx = ax - gap;
  int rx = ax + aw + gap;
  int rx_limit = display.width() - right_reserve;
  bool lfit = true, rfit = true;
  for (int k = 1; k <= count / 2 && (lfit || rfit); k++) {
    int li = (active - k + count) % count;
    int ri = (active + k) % count;
    if (lfit) {
      int avail = lx;   // space from x=0 to the running left edge
      if (avail >= min_w) {
        int tw = ellipsize(display, labels[li], avail - pad * 2, buf, sizeof(buf));
        int w = tw + pad * 2;
        // ellipsize() targets max_w but can overshoot it by a px or two (the
        // ellipsis is re-measured as a whole, so kerning against the last real
        // character isn't accounted for) -- clamp so the pill can never spill
        // past its allotted space (into the screen edge, or a reserved icon
        // on the other side).
        if (w > avail) w = avail;
        drawPill(display, lx - w, w, buf, false);
        lx = lx - w - gap;
      } else lfit = false;
    }
    // Skip the right side when it lands on the same tab as the left (the
    // single opposite tab on an even count) so it isn't drawn twice.
    if (rfit && ri != li) {
      int avail = rx_limit - rx;
      if (avail >= min_w) {
        int tw = ellipsize(display, labels[ri], avail - pad * 2, buf, sizeof(buf));
        int w = tw + pad * 2;
        if (w > avail) w = avail;   // never spill past rx_limit (e.g. into a context-menu icon)
        drawPill(display, rx, w, buf, false);
        rx += w + gap;
      } else rfit = false;
    }
  }
  display.setColor(DisplayDriver::LIGHT);
  display.fillRect(0, display.headerH() - display.sepH(), display.width(), display.sepH());
}

}  // namespace tabbar