udpscope/src/plot_host.cpp

// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: 2026 Martino Ferrari

#include "plot_host.hpp"

#include <algorithm>
#include <cmath>

namespace udpscope {
namespace {

/// A small qualitative palette, one colour per *signal*. It is indexed by the signal
/// rather than by the trace slot so that a signal plotted on several rows is the same
/// colour in all of them: the signal list's chip is what ties a row of that list to a
/// trace on screen, and a colour that depended on where the signal landed would name a
/// different trace in every row.
constexpr plot::u32 kPalette[] = {
    0x4FA3FFu, 0xFF8A4Fu, 0x5FD08Au, 0xE86A9Cu, 0xC9A227u, 0x8F7BFFu, 0x4FD0D0u, 0xFF6B6Bu,
};
constexpr std::size_t kPaletteSize = sizeof(kPalette) / sizeof(kPalette[0]);

/// The chip of a signal that is acquired but on no plot, and of one that is not even
/// acquired. Mid grey: it has to read as "no trace" next to any palette entry.
constexpr plot::u32 kUnplottedColor = 0x6E6E6Eu;

constexpr plot::u32 kCursorAColor = 0xFFD24Fu;
constexpr plot::u32 kCursorBColor = 0x7FE0FFu;
constexpr plot::u32 kRulerColor = 0xB0B0B0u;
constexpr plot::u32 kRulerBColor = 0x8FA8C8u;
/// The measurements' own colour, distinct from both cursor rulers so a readout mark cannot be
/// mistaken for something the user placed.
constexpr plot::u32 kMeasureColor = 0x9BE8A0u;
constexpr plot::u32 kTriggerColor = 0xFF5B5Bu;

constexpr double kParked = -1.0e12;  ///< hides an instrument without removing it

/// The gap between two rows, in device pixels. The rows used to be separate widgets in
/// a box, so there was a widget gap; a figure tiles its viewport, and without a gap two
/// stacked frames read as one tall plot with a line through it.
constexpr plot::f32 kRowGap = 6.0f;

}  // namespace

plot::Color RowSet::palette_color(int index) {
  const std::size_t i = static_cast<std::size_t>(index < 0 ? 0 : index) % kPaletteSize;
  return plot::Color::hex(kPalette[i]);
}

plot::Color RowSet::unplotted_color() { return plot::Color::hex(kUnplottedColor); }

RowSet::RowSet() { rebuild_all(); }

void RowSet::set_row_count(int rows) {
  const int want = std::clamp(rows, 1, kMaxRows);
  if (want == rows_) return;
  rows_ = want;
  // A `Figure`'s row count is fixed at construction, so a new count is a new figure.
  rebuild_all();
}

void RowSet::carry_row(Row& dst, const Row& src) {
  dst.signal_name = src.signal_name;
  dst.name = src.name;
  dst.channel = src.channel;
  dst.color_index = src.color_index;

  dst.ruler_y = src.ruler_y;
  dst.ruler_b_y = src.ruler_b_y;
  // The slot's series stays where it is, but what it is bound to belonged to the row
  // this state came *from*. `bind()` re-resolves every slot next frame; clearing it here
  // is what stops the frame in between from drawing the moved row's data under the new
  // row's legend.
  for (SlotSeries& s : dst.slots) s.bind(nullptr);
}

void RowSet::clear_row(Row& r) {
  r.signal_name = {};
  r.name = {};
  r.channel = {-1, -1, -1, -1};
  r.color_index = {0, 1, 2, 3};
  r.ruler_y = 0.0;
  for (SlotSeries& s : r.slots) s.bind(nullptr);
}

bool RowSet::insert_row(int at) {
  if (rows_ >= kMaxRows) return false;
  const int pos = std::clamp(at, 0, rows_);
  for (int i = rows_; i > pos; --i) carry_row(row(i), row(i - 1));
  clear_row(row(pos));
  ++rows_;
  rebuild_all();
  return true;
}

bool RowSet::remove_row(int at) {
  if (rows_ <= 1 || at < 0 || at >= rows_) return false;
  for (int i = at; i + 1 < rows_; ++i) carry_row(row(i), row(i + 1));
  --rows_;
  clear_row(row(rows_));
  rebuild_all();
  return true;
}

void RowSet::install(Row& r, int /*row_index*/, plot::Plot& p) {
  r.plot = &p;
  r.axis_x = r.plot->add_x_axis(
      {"time", {-1.0, 1.0}, true, plot::AxisPlace::Bottom, false, plot::TickFormat::Time});
  r.axis_y = r.plot->add_y_axis(
      {"value", {-1.0, 1.0}, true, plot::AxisPlace::Left, false, plot::TickFormat::Si});
  for (int s = 0; s < kSlotsPerRow; ++s) {
    const std::size_t i = static_cast<std::size_t>(s);
    r.plot->add_trace(
        {&r.slots[i], palette_color(r.color_index[i]), 1.2f, r.axis_x, r.axis_y, r.name[i]});
  }
  r.cursor_a = r.plot->add_cursor(0.0, plot::Color::hex(kCursorAColor));
  r.cursor_b = r.plot->add_cursor(0.0, plot::Color::hex(kCursorBColor));
  r.ruler = r.plot->add_h_ruler(0.0, plot::Color::hex(kRulerColor));
  r.ruler_b = r.plot->add_h_ruler(0.0, plot::Color::hex(kRulerBColor));
  // The `mix` crossings, one pair per trace slot, hidden until that mode is on. Created
  // here because a `Plot` fixes its annotation set the same way it fixes its traces --
  // `add_annotation()` only appends -- so the markers are made up front and moved.
  for (int s = 0; s < kSlotsPerRow; ++s) {
    plot::Annotation a{0.0, 0.0, "", plot::Color::hex(kCursorAColor), r.axis_x, r.axis_y, false};
    plot::Annotation b{0.0, 0.0, "", plot::Color::hex(kCursorBColor), r.axis_x, r.axis_y, false};
    r.crossing_a[static_cast<std::size_t>(s)] = r.plot->add_annotation(a);
    r.crossing_b[static_cast<std::size_t>(s)] = r.plot->add_annotation(b);
  }
  // The measurements' readout marks: a fixed pool, parked. Levels are rulers (they read a y)
  // and times are markers (they read an x), so the pool has one of each per slot.
  for (int m = 0; m < kMeasureMarks; ++m) {
    const std::size_t mi = static_cast<std::size_t>(m);
    r.measure_h[mi] = r.plot->add_h_ruler(kParked, plot::Color::hex(kMeasureColor));
    r.measure_v[mi] = r.plot->add_cursor(kParked, plot::Color::hex(kMeasureColor));
    // Readouts, not instruments: the pointer must not be able to hover or grab one. Parking
    // them outside the axis and re-placing every frame does not stop a *drag* -- the
    // controller holds the marker for the gesture's life, so it follows the pointer between
    // frames and the readout looks draggable. Excluding it from the hit test is the only
    // place that can say no.
    r.plot->set_cursor_selectable(r.measure_h[mi], false);
    r.plot->set_cursor_selectable(r.measure_v[mi], false);
  }
  r.trigger_marker = r.plot->add_cursor(kParked, plot::Color::hex(kTriggerColor));
  // A marker, not an instrument: it must sit exactly on the edge's time, so its
  // snap is Free and the controller never rounds it onto a sample.
  r.plot->set_cursor_snap(r.trigger_marker, plot::SnapMode::Free);
  // No `set_x_follow(Live)`: the link group owns the window *and* the follow state, and
  // `Figure::link_x()` refuses a member whose x axis still follows on its own.
}

void RowSet::rebuild_all() {
  figure_ = std::make_unique<plot::Figure>(static_cast<plot::u32>(rows_));
  figure_->set_row_gap(kRowGap);
  x_group_ = figure_->add_x_link();
  for (int i = 0; i < kMaxRows; ++i) {
    Row& r = row(i);
    row_dirty_[static_cast<std::size_t>(i)] = false;
    if (i >= rows_) {
      r.plot = nullptr;  // not a row of this figure: nothing to plot into
      continue;
    }
    install(r, i, figure_->plot(static_cast<plot::u32>(i)));
    place_cursors(r);
    if (trigger_marker_on_) {
      r.plot->set_cursor_x(r.trigger_marker, trigger_marker_x_, plot::CursorPlacement::Free);
    }
    figure_->link_x(static_cast<plot::u32>(i), x_group_);
  }
  if (y_gutter_px_ > 0.0) apply_y_gutter();
  // A new figure starts with no window at all, so the one the rows were showing has to
  // be restated -- as the pin it was, if an event is on screen: assigning a trace or
  // changing the row count while a capture is displayed must not throw the view back
  // onto the live edge, which in trigger mode nothing would move it off again until the
  // next latch.
  if (pinned_) {
    pin_event_window(pinned_pre_, pinned_post_);
  } else {
    set_time_window(window_s_);
  }
}

bool RowSet::rebuild_if_dirty() {
  bool any = false;
  for (int i = 0; i < kMaxRows; ++i) {
    if (row_dirty_[static_cast<std::size_t>(i)]) any = true;
  }
  if (!any) return false;
  // One row's legend text changed, which `Plot` cannot express, so its traces have to
  // be created again -- and a row belongs to a figure, so the figure is rebuilt. That
  // costs the plots' CPU state and nothing else: the host keeps its GL context and is
  // handed the new figure.
  rebuild_all();
  return true;
}

void RowSet::assign(int row_index, int slot, std::string signal_name,
                    std::string display_name, int color_index) {
  if (row_index < 0 || row_index >= kMaxRows || slot < 0 || slot >= kSlotsPerRow) return;
  Row& r = row(row_index);
  const std::size_t s = static_cast<std::size_t>(slot);
  r.signal_name[s] = std::move(signal_name);
  r.channel[s] = -1;  // re-resolved by the next bind()
  r.name[s] = std::move(display_name);
  r.color_index[s] = color_index;
  row_dirty_[static_cast<std::size_t>(row_index)] = true;
}

bool RowSet::slot_bound(int row_index, int slot) const {
  if (row_index < 0 || row_index >= kMaxRows || slot < 0 || slot >= kSlotsPerRow) return false;
  return !row(row_index).signal_name[static_cast<std::size_t>(slot)].empty();
}

int RowSet::channel_of(int row_index, int slot) const {
  if (row_index < 0 || row_index >= kMaxRows || slot < 0 || slot >= kSlotsPerRow) return -1;
  return row(row_index).channel[static_cast<std::size_t>(slot)];
}

void RowSet::bind(ScopeModel& model, DisplayMode mode) {
  const std::vector<SignalInfo>& signals = model.signals();
  const std::vector<ChannelInfo>& channels = model.channels();
  for (int i = 0; i < kMaxRows; ++i) {
    Row& r = row(i);
    for (int s = 0; s < kSlotsPerRow; ++s) {
      const std::size_t si = static_cast<std::size_t>(s);
      if (r.signal_name[si].empty()) {
        r.channel[si] = -1;
        r.slots[si].bind(nullptr);
        continue;
      }
      // Resolve the stable identity every frame: the channel list is rebuilt (and
      // renumbered) whenever a signal is enabled, disabled or re-described, and a
      // stored index would then point at a different signal's channel.
      int signal_index = -1;
      for (std::size_t k = 0; k < signals.size(); ++k) {
        if (signals[k].name == r.signal_name[si]) {
          signal_index = static_cast<int>(k);
          break;
        }
      }
      int channel = -1;
      if (signal_index >= 0) {
        for (std::size_t c = 0; c < channels.size(); ++c) {
          if (static_cast<int>(channels[c].signal) == signal_index) {
            channel = static_cast<int>(c);
            break;
          }
        }
      }
      r.channel[si] = channel;
      if (channel < 0) {
        // Its signal is present but not acquired: keep the identity (so enabling it
        // brings the trace back) and plot nothing meanwhile.
        r.slots[si].bind(nullptr);
        continue;
      }
      // The source is the frame's one `DisplayMode`, decided by the caller: `Held` is
      // the frozen snapshot, `Waiting` is blank (armed, nothing captured yet), and both
      // `Live` and `Capturing` are the live ring -- what differs between those two is
      // the *clock*, which the display epoch carries, not the binding.
      const std::size_t ci = static_cast<std::size_t>(channel);
      switch (mode) {
        case DisplayMode::Held:
          if (auto snap = model.event()) {
            r.slots[si].bind_event(std::move(snap), ci);
          } else {
            r.slots[si].bind(nullptr);
          }
          break;
        case DisplayMode::Waiting:
          r.slots[si].bind(nullptr);
          break;
        case DisplayMode::Live:
        case DisplayMode::Capturing:
          r.slots[si].bind(model.live().shared_channel(ci));
          break;
      }
    }
  }
}

bool RowSet::live_edge(double& newest) const {
  bool any = false;
  for (int i = 0; i < rows_; ++i) {
    const Row& r = row(i);
    if (!r.plot) continue;
    double edge = 0.0;
    // Follow-independent: it reads the row's streaming traces, so a row whose own axis
    // is `Off` (which every member of a link group is) still reports its edge.
    if (!r.plot->x_live_edge(r.axis_x, edge)) continue;
    newest = any ? std::max(newest, edge) : edge;
    any = true;
  }
  return any;
}

void RowSet::set_time_window(double seconds) {
  window_s_ = std::max(0.05, seconds);
  pinned_ = false;
  if (!figure_) return;
  figure_->set_x_link_follow(x_group_, plot::XFollow::Live);
  double newest = 0.0;
  if (live_edge(newest)) {
    // Under a following group the range states the span and -- through its maximum --
    // where the window sits behind the live edge, so a maximum *at* the edge is what
    // makes the offset zero and parks the window on the newest sample. Asking for
    // `{0, window}` here instead would state an offset of a whole epoch.
    figure_->set_x_link_range(x_group_, {newest - window_s_, newest});
  } else {
    figure_->set_x_link_range(x_group_, {0.0, window_s_});
  }
}

void RowSet::set_y_auto(int row_index, bool on) {
  Row& r = row(row_index);
  if (!r.plot) return;
  r.plot->set_y_auto_scale(r.axis_y, on);
  if (on) r.plot->auto_fit_y(r.axis_y);
}

void RowSet::set_y_range(int row_index, double lo, double hi) {
  Row& r = row(row_index);
  if (!r.plot) return;
  const double a = std::min(lo, hi);
  const double b = std::max(lo, hi);
  if (!std::isfinite(a) || !std::isfinite(b) || !(b > a)) return;
  r.plot->set_y_range(r.axis_y, {a, b});
}

void RowSet::place_cursors(Row& r) {
  if (!r.plot) return;
  const bool on = cursors_on_;
  // Which instruments the mode uses; the rest are parked (a `Plot` cannot drop a
  // cursor, so hiding is the only way to take one off screen).
  const bool vertical = on && cursor_mode_ != CursorMode::Horizontal;
  const bool horizontal = on && (cursor_mode_ == CursorMode::Horizontal ||
                                 cursor_mode_ == CursorMode::Both);
  r.plot->set_cursor_x(r.cursor_a, vertical ? cursor_a_x_ : kParked);
  r.plot->set_cursor_x(r.cursor_b, vertical ? cursor_b_x_ : kParked);
  r.plot->set_cursor_y(r.ruler, horizontal ? r.ruler_y : kParked);
  r.plot->set_cursor_y(r.ruler_b, horizontal ? r.ruler_b_y : kParked);
}

void RowSet::set_cursor_mode(CursorMode mode) {
  if (mode == cursor_mode_) return;
  cursor_mode_ = mode;
  for (int i = 0; i < kMaxRows; ++i) place_cursors(row(i));
  place_crossings();
}

void RowSet::place_crossings() {
  const bool mix = cursor_mode_ == CursorMode::Mix && cursors_visible();
  for (int i = 0; i < kMaxRows; ++i) {
    Row& r = row(i);
    if (!r.plot) continue;
    for (int s = 0; s < kSlotsPerRow; ++s) {
      const std::size_t si = static_cast<std::size_t>(s);
      const plot::u32 ida = r.crossing_a[si];
      const plot::u32 idb = r.crossing_b[si];
      if (ida >= r.plot->annotation_count() || idb >= r.plot->annotation_count()) continue;
      plot::Annotation a = r.plot->annotation(ida);
      plot::Annotation b = r.plot->annotation(idb);
      double ya = 0.0;
      double yb = 0.0;
      const bool has_a = mix && r.plot->crosshair_value(static_cast<plot::u32>(s), cursor_a_x_, ya);
      const bool has_b = mix && r.plot->crosshair_value(static_cast<plot::u32>(s), cursor_b_x_, yb);
      a.visible = has_a;
      b.visible = has_b;
      if (has_a) {
        a.x = cursor_a_x_;
        a.y = ya;
      }
      if (has_b) {
        b.x = cursor_b_x_;
        b.y = yb;
      }
      r.plot->set_annotation(ida, a);
      r.plot->set_annotation(idb, b);
    }
  }
}

double RowSet::ruler_y(int r) const {
  return r >= 0 && r < rows_ ? row(r).ruler_y : 0.0;
}

double RowSet::ruler_b_y(int r) const {
  return r >= 0 && r < rows_ ? row(r).ruler_b_y : 0.0;
}

int RowSet::crossings_visible() const {
  int n = 0;
  for (int i = 0; i < rows_; ++i) {
    const Row& r = row(i);
    if (!r.plot) continue;
    for (int s = 0; s < kSlotsPerRow; ++s) {
      const std::size_t si = static_cast<std::size_t>(s);
      if (r.crossing_a[si] < r.plot->annotation_count() &&
          r.plot->annotation(r.crossing_a[si]).visible) {
        ++n;
      }
      if (r.crossing_b[si] < r.plot->annotation_count() &&
          r.plot->annotation(r.crossing_b[si]).visible) {
        ++n;
      }
    }
  }
  return n;
}

bool RowSet::crossing_at(int i, int slot, bool second, double& x, double& y) const {
  if (i < 0 || i >= rows_ || slot < 0 || slot >= kSlotsPerRow) return false;
  const Row& r = row(i);
  if (!r.plot) return false;
  const std::size_t si = static_cast<std::size_t>(slot);
  const plot::u32 id = second ? r.crossing_b[si] : r.crossing_a[si];
  if (id >= r.plot->annotation_count()) return false;
  const plot::Annotation& a = r.plot->annotation(id);
  if (!a.visible) return false;
  x = a.x;
  y = a.y;
  return true;
}

void RowSet::set_measure_marks(const std::vector<MeasureMark>& marks) {
  measure_marks_placed_ = static_cast<int>(marks.size());
  for (int i = 0; i < kMaxRows; ++i) {
    Row& r = row(i);
    if (!r.plot) continue;
    int h = 0;
    int v = 0;
    for (const MeasureMark& m : marks) {
      if (m.row != i) continue;
      if (m.level) {
        if (h >= kMeasureMarks) continue;
        const std::size_t mi = static_cast<std::size_t>(h++);
        r.plot->set_cursor_y(r.measure_h[mi], m.value, plot::CursorPlacement::Free);
        r.plot->set_cursor_color(r.measure_h[mi], plot::Color::hex(m.color));
      } else {
        if (v >= kMeasureMarks) continue;
        const std::size_t mi = static_cast<std::size_t>(v++);
        r.plot->set_cursor_x(r.measure_v[mi], m.value, plot::CursorPlacement::Free);
        r.plot->set_cursor_color(r.measure_v[mi], plot::Color::hex(m.color));
      }
    }
    // What the measurements left over is parked rather than kept: a stale readout at the old
    // window's position is worse than none.
    for (; h < kMeasureMarks; ++h) {
      r.plot->set_cursor_y(r.measure_h[static_cast<std::size_t>(h)], kParked);
    }
    for (; v < kMeasureMarks; ++v) {
      r.plot->set_cursor_x(r.measure_v[static_cast<std::size_t>(v)], kParked);
    }
  }
}

void RowSet::fit_x() {
  Row& first = row(0);
  if (!first.plot || !figure_) return;
  first.plot->auto_fit_x();
  const plot::Range fitted = first.plot->x_range(first.axis_x);
  const double span = fitted.span();
  if (!std::isfinite(span) || !(span > 0.0)) return;
  // The same two paths `fit_all()` takes: a held event owns its window and states it
  // through the link group, a live view re-arms the follow and frames the newest span.
  if (pinned_) {
    window_s_ = span;
    figure_->set_x_link_range(x_group_, fitted);
  } else {
    set_time_window(span);
  }
}

void RowSet::sync_cursors() {
  if (!cursors_visible()) return;
  // Only a mode that *shows* the vertical pair reads them back. With them parked (the
  // `horizontal` mode) whatever the plot reports is our own park coming back -- and a
  // snapped cursor parked far outside the axis reads back as something finite, which
  // would be adopted as a gesture and destroy the shared times.
  // Anything within this much of what we last pushed is our own placement coming back
  // (the plot stores f64, so an exact compare would be brittle across a rebuild).
  const auto moved = [](double a, double b) {
    return std::fabs(a - b) > 1.0e-9 * std::max(1.0, std::fabs(b));
  };
  bool push = false;
  for (int i = 0; i < rows_; ++i) {
    Row& r = row(i);
    if (!r.plot) continue;
    // A gesture writes the *plot*; this is the only place its result is visible. A
    // ruler is its own row's value -- nothing to share, but it still has to be read
    // back or the pane would keep showing wherever the app last put it.
    const bool rulers = cursor_mode_ == CursorMode::Horizontal || cursor_mode_ == CursorMode::Both;
    if (rulers) {
      const double y = r.plot->cursor(r.ruler).y;
      const double yb = r.plot->cursor(r.ruler_b).y;
      if (y > kParked * 0.5) r.ruler_y = y;
      if (yb > kParked * 0.5) r.ruler_b_y = yb;
    }
    if (cursor_mode_ == CursorMode::Horizontal) continue;  // the pair is parked: not a value
    const double a = r.plot->cursor(r.cursor_a).x;
    const double b = r.plot->cursor(r.cursor_b).x;
    if (a < kParked * 0.5 || b < kParked * 0.5) continue;  // parked: not a value
    if (moved(a, cursor_a_x_)) {
      cursor_a_x_ = a;
      push = true;
    }
    if (moved(b, cursor_b_x_)) {
      cursor_b_x_ = b;
      push = true;
    }
  }
  if (push) {
    for (int i = 0; i < rows_; ++i) place_cursors(row(i));
  }
  place_crossings();
}

void RowSet::clamp_to_data() {
  if (!figure_) return;
  // The rows share one window, so they share one bound: the union of what they hold.
  // Taking each row's own would let a row whose signal was enabled a moment ago clamp
  // the window every row is looking at.
  plot::Range data{};
  bool have = false;
  for (int i = 0; i < rows_; ++i) {
    Row& r = row(i);
    if (!r.plot) continue;
    const plot::data::Series* series = nullptr;
    for (int s = 0; s < kSlotsPerRow && series == nullptr; ++s) {
      if (!r.signal_name[static_cast<std::size_t>(s)].empty()) {
        series = r.slots[static_cast<std::size_t>(s)].bound();
      }
    }
    if (series == nullptr || series->size() < 2) continue;
    const plot::Range b = series->x_bounds();
    if (!std::isfinite(b.min) || !std::isfinite(b.max) || !(b.max > b.min)) continue;
    data = have ? plot::Range{std::min(data.min, b.min), std::max(data.max, b.max)} : b;
    have = true;
  }
  if (!have) return;
  const double retained = data.max - data.min;
  const double span = figure_->x_link_range(x_group_).span();
  if (!(span > 0.0) || !std::isfinite(span)) return;
  // The *requested* window is intent, and a buffer that has not filled it yet must not
  // be allowed to redefine it. This runs every frame and cannot tell "the user zoomed
  // out past the data" from "the ring has only just started filling", and the first
  // frames after a signal is enabled hold a couple of hundred samples: clamping to
  // those shrank a requested 2 s window to ~0.02 s, and nothing here ever grows a span
  // back, so the view stayed pinned to the newest 20 ms of a 6.5 s buffer for the rest
  // of the run. That is the loudest form of the "live trace is clipped, only the most
  // recent part is visible, data is there because the crosshair reads it" defect -- the
  // data was never clipped at all, the window was. Clamping against `max(retained,
  // window_s_)` leaves a partly filled window empty on its left, which is what a scope
  // that just started should look like.
  //
  // The span only. A pan is the group's `offset` behind its live edge and the group
  // clamps it against what its members retain on every layout, so there is nothing
  // here to do about `view.min < data.min` -- and doing it anyway would state a maximum
  // away from the live edge, i.e. ask the group to scroll back.
  const double limit = std::max(retained, window_s_);
  if (span > limit) figure_->set_x_link_range(x_group_, {data.max - limit, data.max});
}

void RowSet::pin_event_window(double pre_s, double post_s) {
  window_s_ = std::max(1.0e-3, pre_s + post_s);
  pinned_ = true;
  pinned_pre_ = pre_s;
  pinned_post_ = post_s;
  if (!figure_) return;
  // The captured event sits at [-pre, +post] with the edge at 0, and the bound series is
  // the immutable snapshot. The group must stop following first: Live re-derives the
  // window from a live edge, and with nothing streaming it would keep placing the window
  // from the last stale edge instead of the event.
  figure_->set_x_link_follow(x_group_, plot::XFollow::Off);
  figure_->set_x_link_range(x_group_, {-pre_s, post_s});
}

void RowSet::fit_all() {
  for (int i = 0; i < rows_; ++i) {
    Row& r = row(i);
    if (r.plot) r.plot->auto_fit_y(r.axis_y);
  }
  Row& first = row(0);
  if (!first.plot || !figure_) return;
  // Row 0 fits its own x to the data it holds; that span becomes the shared window, and
  // stating it through the group is what puts every row on it.
  first.plot->auto_fit_x();
  const plot::Range fitted = first.plot->x_range(first.axis_x);
  const double span = fitted.span();
  if (!std::isfinite(span) || !(span > 0.0)) return;
  if (pinned_) {
    // Fitting a captured event: the window is the snapshot's own `[-pre, +post]` span,
    // and `set_time_window()` would re-arm the follow and re-frame on a live edge that
    // trigger mode has nothing bound to.
    window_s_ = span;
    figure_->set_x_link_range(x_group_, fitted);
  } else {
    set_time_window(span);
  }
}

void RowSet::note_y_gutter(double need_px) {
  double want = std::min(need_px + 6.0, 200.0);
  // Reserve room for the widest label the formatter can produce, once, with the
  // font the labels are actually drawn in (the embedded font is monospaced, so a
  // character count is an exact width).
  if (!y_gutter_reserved_) {
    for (int i = 0; i < rows_; ++i) {
      Row& r = row(i);
      if (!r.plot) continue;
      const plot::render::TextBackend* text = r.plot->text_backend();
      if (text == nullptr) continue;
      const plot::render::Style& style = r.plot->style();
      const double advance = double(text->measure("0123456789")) / 10.0;
      const double pad = double(style.device(style.grid_label_pad));
      // "-1.23e-45" is the longest label `format_si()`'s fallback can print.
      want = std::max(want, 9.0 * advance + 2.0 * pad + 2.0);
      y_gutter_reserved_ = true;
      break;
    }
  }
  if (want > y_gutter_px_) y_gutter_px_ = want;
}

void RowSet::apply_y_gutter() {
  if (!figure_ || !(y_gutter_px_ > 0.0)) return;
  figure_->set_min_y_gutter(static_cast<f32>(y_gutter_px_));
}

void RowSet::set_trigger_marker(double x, bool visible) {
  trigger_marker_on_ = visible;
  trigger_marker_x_ = x;
  const double want = visible ? x : kParked;
  for (int i = 0; i < rows_; ++i) {
    Row& r = row(i);
    if (!r.plot) continue;
    // Re-assert against what the plot *holds*, not against a cached value: the
    // marker is a cursor, so the input layer will happily drag it, and a marker the
    // user can move off the trigger instant is not marking anything. Comparing
    // with the plot also keeps the steady state write-free (a write invalidates the
    // plot's cached measurements).
    if (r.plot->cursor(r.trigger_marker).x == want) continue;
    r.plot->set_cursor_x(r.trigger_marker, want, plot::CursorPlacement::Free);
  }
}

void RowSet::set_cursors_visible(bool on) {
  cursors_on_ = on;
  for (int i = 0; i < kMaxRows; ++i) place_cursors(row(i));
}

void RowSet::reset_cursors() {
  for (int i = 0; i < kMaxRows; ++i) {
    Row& r = row(i);
    if (!r.plot) continue;
    const plot::Range xr = r.plot->x_range(r.axis_x);
    const double span = xr.span() > 0.0 ? xr.span() : window_s_;
    cursor_a_x_ = xr.min + 0.25 * span;
    cursor_b_x_ = xr.min + 0.75 * span;
    const double y_lo = r.plot->y_range(r.axis_y).min;
    const double y_span = r.plot->y_range(r.axis_y).span();
    r.ruler_y = y_lo + 0.35 * (y_span > 0.0 ? y_span : 1.0);
    r.ruler_b_y = y_lo + 0.65 * (y_span > 0.0 ? y_span : 1.0);
  }
  // Every row's instruments are written from what was just set. Without this the plots
  // keep their build-time cursors (x = 0) and `sync_cursors()` -- which reads the plots
  // because a *gesture* writes them -- adopts that zero as a moved cursor.
  for (int i = 0; i < kMaxRows; ++i) place_cursors(row(i));
  place_crossings();
}

}  // namespace udpscope