adapters: route pointer events by cell rect

adapters/glfw/glfw_host.cpp

@@ -455,9 +455,11 @@ void Host::set_figure(Figure* figure) noexcept {
     row_rects_.clear();  // no figure, no rows: the handlers fall back to `controller_`
     return;
   }
-  const u32 rows = figure_->row_count();
-  row_controllers_.reserve(rows);
-  for (u32 i = 0; i < rows; ++i) {
+  // One controller per **plot** (a row of several cells has one for each), indexed by the
+  // flattened plot index the figure uses.
+  const u32 plots = figure_->plot_count();
+  row_controllers_.reserve(plots);
+  for (u32 i = 0; i < plots; ++i) {
     row_controllers_.push_back(std::make_unique<input::Controller>(figure_->plot(i)));
   }
   // The new figure's rects go into the cache now, not at the next frame: an event
@@ -469,8 +471,10 @@ void Host::set_figure(Figure* figure) noexcept {
 
 void Host::refresh_row_rects() noexcept {
   // The one `Figure::layout()` per call: every event handler reads `row_rects_`
-  // instead of paying this again, which is the whole point of the cache (R7).
-  row_rects_ = figure_ != nullptr ? figure_->layout().rows : std::vector<Rect>{};
+  // instead of paying this again, which is the whole point of the cache (R7). The rects
+  // are the figure's **cells** (one per plot, flattened), which for a figure with one
+  // cell per row are exactly its row rects.
+  row_rects_ = figure_ != nullptr ? figure_->layout().cells : std::vector<Rect>{};
 }
 
 input::Controller* Host::row_controller(u32 row) noexcept {
@@ -486,8 +490,7 @@ input::Controller& Host::controller_at(f32 x, f32 y) noexcept {
   // frame stale, which is the documented worst case.
   const std::vector<Rect>& rows = row_rects_;
   if (rows.empty() || rows.size() != row_controllers_.size()) return controller_;
-  (void)x;  // the rows tile the figure vertically, so y alone picks one -- see row_in()
-  const u32 row = row_in(rows, y);
+  const u32 row = row_in(rows, x, y);
   last_row_ = row;
   input::Controller& controller = *row_controllers_[row];
   // The row's own viewport, so the geometry this controller hit-tests is the geometry
@@ -506,7 +509,6 @@ void Host::feed_pointer_event(const input::PointerEvent& e) noexcept {
 
 input::Controller& Host::pointer_target(f32 x, f32 y, input::Button button, bool pressed,
                                         bool released) noexcept {
-  (void)x;  // the rows tile the figure vertically, so y alone picks one -- see row_in()
   if (figure_ == nullptr || row_controllers_.empty()) return controller_;
   const std::vector<Rect>& rows = row_rects_;
   if (rows.empty() || rows.size() != row_controllers_.size()) return controller_;
@@ -523,7 +525,7 @@ input::Controller& Host::pointer_target(f32 x, f32 y, input::Button button, bool
     // drag, and its press must not steal the capture to the row it landed in.
     if (released && button == captured_button_) captured_ = false;
   } else {
-    row = row_in(rows, y);
+    row = row_in(rows, x, y);
     if (pressed) {
       captured_ = true;
       captured_row_ = row;
@@ -541,27 +543,29 @@ input::Controller& Host::pointer_target(f32 x, f32 y, input::Button button, bool
 
 u32 Host::pointer_row(const std::vector<Rect>& rows) noexcept {
   if (captured_ && captured_row_ < rows.size()) return captured_row_;
-  return row_in(rows, last_pointer_y_);
+  return row_in(rows, last_pointer_x_, last_pointer_y_);
 }
 
-u32 Host::row_in(const std::vector<Rect>& rows, f32 y) noexcept {
+u32 Host::row_in(const std::vector<Rect>& rows, f32 x, f32 y) noexcept {
   if (rows.empty()) return 0u;
-  // The row the pixel is in, or -- when it is in none of them, which is the row gap a
-  // host has asked for with `Figure::set_row_gap()` or the figure's own margins -- the
-  // row whose rect is nearest. Selection by distance rather than by "the first that
-  // matches" is what makes a pixel in a gap belong to the row it is *near*: the rows
-  // tile the figure at the default gap of 0, so this is unreachable until a host asks
-  // for one, and a gesture in a visible gap must not be routed to row 0 by default.
+  // The cell the pixel is in, or -- when it is in none of them, which is the row gap or
+  // column gap a host has asked for with `Figure::set_row_gap()`/`set_col_gap()` or the
+  // figure's own margins -- the cell whose rect is nearest (squared distance from the
+  // pixel to the rect). Selection by distance rather than by "the first that matches" is
+  // what makes a pixel in a gap belong to the cell it is *near*, and a gesture in a
+  // visible gap must not be routed to plot 0 by default. For a figure with one cell per
+  // row every cell spans the figure's width, so this reduces to the nearest row by y.
   u32 row = 0u;
   f32 best = std::numeric_limits<f32>::infinity();
   for (u32 i = 0; i < rows.size(); ++i) {
-    const f32 top = rows[i].y;
-    const f32 bottom = rows[i].y + rows[i].h;
-    const f32 distance = y < top ? top - y : (y >= bottom ? y - bottom : 0.0f);
+    const Rect& r = rows[i];
+    const f32 dx = x < r.x ? r.x - x : (x >= r.right() ? x - r.right() : 0.0f);
+    const f32 dy = y < r.y ? r.y - y : (y >= r.bottom() ? y - r.bottom() : 0.0f);
+    const f32 distance = dx * dx + dy * dy;
     if (distance < best) {
       best = distance;
       row = i;
-      if (distance == 0.0f) break;  // inside this row: nothing can be nearer
+      if (distance == 0.0f) break;  // inside this cell: nothing can be nearer
     }
   }
   return row;

adapters/glfw/glfw_host.hpp

@@ -121,18 +121,21 @@ class Host {
   /// `plot_` is then untouched by any of this.
   void set_figure(Figure* figure) noexcept;
   Figure* figure() noexcept { return figure_; }
-  /// One figure row's controller -- the one a gesture on that row reaches -- or
-  /// null while no figure is set or the row does not exist. A host reads a drag
+  /// One figure plot's controller -- the one a gesture on that plot reaches -- or null
+  /// while no figure is set or it does not exist. `row` is the **flattened plot index**
+  /// (`Figure::plot_count()` of them: the row count when no row holds several cells). A host reads a drag
   /// mode or a hover out of it (`controller()` is the single-plot loop's, and is
   /// not the one figure gestures go to).
   input::Controller* row_controller(u32 row) noexcept;
   /// The controller an event at framebuffer pixel (x, y) belongs to: `controller_` --
   /// the single-plot loop -- while no figure is set, and the controller of the figure
-  /// row that pixel lands in otherwise. The row rects come from the cache
+  /// plot (cell) that pixel lands in otherwise -- x and y both pick it, as a row may hold
+  /// several cells side by side. The cell rects come from the cache
   /// `refresh_row_rects()` fills -- the same ones the renderer draws -- so a gesture
   /// lands on the row it was aimed at and no event lays the figure out; a pixel
-  /// inside no row -- the row gap a host asked for with `Figure::set_row_gap()`,
-  /// or a margin -- is the *nearest* row rather than dropped or defaulted, so a drag
+  /// inside no cell -- the row or column gap a host asked for with
+  /// `Figure::set_row_gap()`/`set_col_gap()`, or a margin -- is the *nearest* cell rather than
+  /// dropped or defaulted, so a drag
   /// that leaves the data area still ends where it should.
   ///
   /// It also hands that row its own viewport, which is what keeps the controller's
@@ -217,11 +220,12 @@ class Host {
   void on_scroll(f64 dx, f64 dy) noexcept;
   void on_key(int key, int action, int mods) noexcept;
 
-  /// The index of the row of `rows` a framebuffer y belongs to: the row it is in, or the nearest
-  /// row when it is in none (a row gap, a margin outside the figure). One rule, shared by the event
-  /// routing and the crosshair sync -- and taking the rects rather than reading them, so a caller
-  /// that has just laid the figure out does not make it lay out again for this.
-  static u32 row_in(const std::vector<Rect>& rows, f32 y) noexcept;
+  /// The index of the cell of `rows` (the figure's flattened cell rects) a framebuffer pixel
+  /// belongs to: the cell it is in, or the nearest cell when it is in none (a row or column gap,
+  /// a margin outside the figure). One rule, shared by the event routing and the crosshair sync
+  /// -- and taking the rects rather than reading them, so a caller that has just laid the figure
+  /// out does not make it lay out again for this.
+  static u32 row_in(const std::vector<Rect>& rows, f32 x, f32 y) noexcept;
 
   /// The controller a pointer event at (x, y) belongs to, applying the button capture:
   /// a press claims the row it landed in (`captured_row_` + `captured_button_`) and
@@ -231,10 +235,10 @@ class Host {
   input::Controller& pointer_target(f32 x, f32 y, input::Button button, bool pressed,
                                     bool released) noexcept;
 
-  /// The row the pointer's events currently go to: the captured row while a drag owns
-  /// the button, the row under the pointer otherwise. The run loop uses it to clear
-  /// every *other* row's hot handles, so a row the pointer left cannot keep drawing a
-  /// hover or a grab it last published.
+  /// The plot (flattened index) the pointer's events currently go to: the captured one
+  /// while a drag owns the button, the one under the pointer otherwise. The run loop uses
+  /// it to clear every *other* plot's hot handles, so one the pointer left cannot keep
+  /// drawing a hover or a grab it last published.
   u32 pointer_row(const std::vector<Rect>& rows) noexcept;
 
   /// Spreads the hover over a whole `Figure` (spec §15).
@@ -292,7 +296,7 @@ class Host {
   u32 captured_row_ = 0u;
   input::Button captured_button_ = input::Button::Left;
 
-  /// The figure's row rects as of the last `refresh_row_rects()` -- the cache the
+  /// The figure's cell rects (one per plot, flattened; the row rects when no row is split) as of the last `refresh_row_rects()` -- the cache the
   /// event routing reads instead of laying the figure out per event (R7). Filled by
   /// `set_figure()` and once per frame by the run loop; empty while no figure is
   /// set, which is the state `controller_at()`/`pointer_target()` fall back to the

adapters/gtk4/gtk_plot_area.cpp

@@ -245,9 +245,11 @@ void PlotArea::set_figure(Figure* figure) noexcept {
     row_rects_.clear();  // no figure, no rows: the routing falls back to `controller_`
     return;
   }
-  const u32 rows = figure_->row_count();
-  row_controllers_.reserve(rows);
-  for (u32 i = 0; i < rows; ++i) {
+  // One controller per **plot** (a row of several cells has one for each), indexed by the
+  // flattened plot index the figure uses.
+  const u32 plots = figure_->plot_count();
+  row_controllers_.reserve(plots);
+  for (u32 i = 0; i < plots; ++i) {
     row_controllers_.push_back(std::make_unique<input::Controller>(figure_->plot(i)));
   }
   // The new figure's geometry goes into the cache now, not at the next frame: an event
@@ -269,8 +271,10 @@ void PlotArea::lay_figure_out(Rect px) noexcept {
 
 void PlotArea::refresh_row_rects() noexcept {
   // The one `Figure::layout()` per call: every event handler reads `row_rects_`
-  // instead of paying this again, which is the whole point of the cache.
-  row_rects_ = figure_ != nullptr ? figure_->layout().rows : std::vector<Rect>{};
+  // instead of paying this again, which is the whole point of the cache. The rects are
+  // the figure's **cells** (one per plot, flattened), which for a figure with one cell
+  // per row are exactly its row rects.
+  row_rects_ = figure_ != nullptr ? figure_->layout().cells : std::vector<Rect>{};
 }
 
 input::Controller* PlotArea::row_controller(u32 row) noexcept {
@@ -283,8 +287,7 @@ input::Controller& PlotArea::controller_at(f32 x, f32 y) noexcept {
   // -- and not a fresh `Figure::layout()`: an event pays no layout, or a burst of
   // pointer motion over a multi-row figure would re-lay every row out per move.
   if (row_rects_.empty() || row_rects_.size() != row_controllers_.size()) return controller_;
-  (void)x;  // the rows tile the figure vertically, so y alone picks one -- see row_in()
-  const u32 row = row_in(row_rects_, y);
+  const u32 row = row_in(row_rects_, x, y);
   input::Controller& controller = *row_controllers_[row];
   controller.set_viewport(row_rects_[row]);
   return controller;
@@ -292,11 +295,11 @@ input::Controller& PlotArea::controller_at(f32 x, f32 y) noexcept {
 
 u32 PlotArea::row_at(double x, double y) const noexcept {
   if (figure_ == nullptr || row_rects_.empty()) return 0;
-  (void)x;
-  return row_in(row_rects_, to_device(x, y).y);
+  const Vec2 p = to_device(x, y);
+  return row_in(row_rects_, p.x, p.y);
 }
 
-input::Controller& PlotArea::target_controller(f32 y) noexcept {
+input::Controller& PlotArea::target_controller(f32 x, f32 y) noexcept {
   if (figure_ == nullptr || row_controllers_.empty()) return controller_;
   if (row_rects_.empty() || row_rects_.size() != row_controllers_.size()) return controller_;
   // The capture: while a press is open the gesture belongs to the row that press
@@ -304,7 +307,7 @@ input::Controller& PlotArea::target_controller(f32 y) noexcept {
   // the release to the row the pointer is over *now* would leave the first row's drag
   // open for ever -- its controller never sees the release that ends it -- and let a
   // later gesture resume it from the stale anchor.
-  u32 row = press_open_ ? press_row_ : row_in(row_rects_, y);
+  u32 row = press_open_ ? press_row_ : row_in(row_rects_, x, y);
   // Re-read against this frame's rects: the widget can be resized mid-drag, and the
   // guard keeps a stale index from reaching past the controller list.
   if (row >= row_controllers_.size()) row = 0;
@@ -314,23 +317,25 @@ input::Controller& PlotArea::target_controller(f32 y) noexcept {
   return controller;
 }
 
-u32 PlotArea::row_in(const std::vector<Rect>& rows, f32 y) noexcept {
+u32 PlotArea::row_in(const std::vector<Rect>& rows, f32 x, f32 y) noexcept {
   if (rows.empty()) return 0;
-  // The row the pixel is in, or -- when it is in none of them, which is the row gap a
-  // host asked for with `Figure::set_row_gap()` or the figure's own margins -- the row
-  // whose rect is nearest. By distance rather than by "the first that matches": the
-  // rows tile the figure at the default gap of 0, so this is unreachable until a host
-  // asks for a gap, and a gesture in a visible gap must not default to row 0.
+  // The cell the pixel is in, or -- when it is in none of them, which is the row or
+  // column gap a host asked for with `Figure::set_row_gap()`/`set_col_gap()` or the
+  // figure's own margins -- the cell whose rect is nearest (squared distance from the
+  // pixel to the rect). By distance rather than by "the first that matches": a gesture
+  // in a visible gap must not default to plot 0. For a figure with one cell per row
+  // every cell spans the figure's width, so this reduces to the nearest row by y.
   u32 row = 0;
   f32 best = std::numeric_limits<f32>::infinity();
   for (u32 i = 0; i < rows.size(); ++i) {
-    const f32 top = rows[i].y;
-    const f32 bottom = rows[i].y + rows[i].h;
-    const f32 distance = y < top ? top - y : (y >= bottom ? y - bottom : 0.0f);
+    const Rect& r = rows[i];
+    const f32 dx = x < r.x ? r.x - x : (x >= r.right() ? x - r.right() : 0.0f);
+    const f32 dy = y < r.y ? r.y - y : (y >= r.bottom() ? y - r.bottom() : 0.0f);
+    const f32 distance = dx * dx + dy * dy;
     if (distance < best) {
       best = distance;
       row = i;
-      if (distance == 0.0f) break;  // inside this row: nothing can be nearer
+      if (distance == 0.0f) break;  // inside this cell: nothing can be nearer
     }
   }
   return row;
@@ -341,7 +346,7 @@ u32 PlotArea::pointer_row() const noexcept {
   // The captured row while a press owns the gesture, so an in-flight drag keeps its
   // highlight even after the pointer has left the row it began in.
   if (press_open_ && press_row_ < row_rects_.size()) return press_row_;
-  return row_in(row_rects_, pointer_.y);
+  return row_in(row_rects_, pointer_.x, pointer_.y);
 }
 
 void PlotArea::sync_selection_frames() noexcept {
@@ -616,7 +621,7 @@ void PlotArea::pointer_press(input::Button button, u32 mods, double x, double y,
   // The figure row this gesture belongs to for its whole life, claimed from the press's
   // own position *before* the event is dispatched (see `target_controller()`). Harmless
   // and unread while no figure is set.
-  press_row_ = figure_ != nullptr ? row_in(row_rects_, p.y) : 0;
+  press_row_ = figure_ != nullptr ? row_in(row_rects_, p.x, p.y) : 0;
   press_open_ = true;
   press_button_ = button;
   press_mods_ = mods;
@@ -634,7 +639,7 @@ void PlotArea::pointer_press(input::Button button, u32 mods, double x, double y,
   e.down = true;
   e.pressed = true;
   e.time_s = pointer_time_s(time_ms);  // the double-click detector differences these
-  target_controller(p.y).on_pointer(e);
+  target_controller(p.x, p.y).on_pointer(e);
   gtk_gl_area_queue_render(GTK_GL_AREA(widget_));
 }
 
@@ -643,7 +648,7 @@ void PlotArea::pointer_release(Vec2 position, u32 time_ms) noexcept {
   // Resolved while the press is still open, so the release reaches the row the press
   // claimed rather than the row the pointer ended over -- the controller that owns the
   // drag is the only one that can close it.
-  input::Controller& target = target_controller(position.y);
+  input::Controller& target = target_controller(position.x, position.y);
   press_open_ = false;
 
   input::PointerEvent e;
@@ -748,7 +753,7 @@ void PlotArea::on_drag_update(GtkGestureDrag* gesture, double offset_x, double o
       gtk_event_controller_get_current_event_time(GTK_EVENT_CONTROLLER(gesture)));
   // The press's row, not the row the pointer has reached: `press_open_` is true here,
   // so a drag that crosses a row boundary stays with the controller that began it.
-  area->target_controller(sample.position.y).on_pointer(e);
+  area->target_controller(sample.position.x, sample.position.y).on_pointer(e);
   gtk_gl_area_queue_render(GTK_GL_AREA(area->widget_));
 }
 
@@ -795,7 +800,7 @@ void PlotArea::on_zoom_scale_changed(GtkGestureZoom* gesture, double scale,
       static_cast<f32>(scale), Vec2{static_cast<f32>(cx), static_cast<f32>(cy)}, area->mapping_);
   // The folded event carries the focal point, which is the position this pinch belongs
   // to; while a press is open the capture overrides it, as it does for a drag.
-  area->target_controller(g.y).on_gesture(g);
+  area->target_controller(g.x, g.y).on_gesture(g);
   gtk_gl_area_queue_render(GTK_GL_AREA(area->widget_));
 }
 
@@ -834,7 +839,7 @@ int PlotArea::on_scroll(GtkEventControllerScroll* scroll, double dx, double dy,
   e.dx = static_cast<f32>(scroll_notches(dx, unit));
   e.dy = static_cast<f32>(notches);
   e.mods = gesture_mods(GTK_EVENT_CONTROLLER(scroll));
-  area->target_controller(at.y).on_wheel(e);
+  area->target_controller(at.x, at.y).on_wheel(e);
   gtk_gl_area_queue_render(GTK_GL_AREA(area->widget_));
   return TRUE;  // consumed: the plot zoomed
 }
@@ -858,7 +863,7 @@ void PlotArea::on_motion(GtkEventControllerMotion* motion, double x, double y, v
   e.down = false;
   e.time_s = PlotArea::pointer_time_s(
       gtk_event_controller_get_current_event_time(GTK_EVENT_CONTROLLER(motion)));
-  area->target_controller(p.y).on_pointer(e);
+  area->target_controller(p.x, p.y).on_pointer(e);
 }
 
 // --- keyboard -------------------------------------------------------------

adapters/gtk4/gtk_plot_area.hpp

@@ -260,15 +260,17 @@ class PlotArea {
   Figure* figure() noexcept { return figure_; }
   const Figure* figure() const noexcept { return figure_; }
 
-  /// One figure row's controller -- the one a gesture on that row reaches -- or null
-  /// while no figure is set or the row does not exist. A host reads a drag mode or a
+  /// One figure plot's controller -- the one a gesture on that plot reaches -- or null
+  /// while no figure is set or it does not exist. `row` is the **flattened plot index**
+  /// (`Figure::plot_count()` of them: the row count when no row holds several cells). A host reads a drag mode or a
   /// hover out of it.
   input::Controller* row_controller(u32 row) noexcept;
 
   /// The controller an event at device pixel `(x, y)` belongs to: `controller()`
-  /// while no figure is set, and otherwise the controller of the figure row that
-  /// pixel lands in -- a pixel inside no row (a `Figure::set_row_gap()` gap, a
-  /// margin) is the *nearest* row rather than dropped, so a drag that leaves the data
+  /// while no figure is set, and otherwise the controller of the figure plot (cell)
+  /// that pixel lands in -- x and y both pick it, as a row may hold several cells side
+  /// by side. A pixel inside no cell (a `Figure::set_row_gap()`/`set_col_gap()` gap, a
+  /// margin) is the *nearest* cell rather than dropped, so a drag that leaves the data
   /// area still ends where it should. It also hands that row its own viewport, which
   /// is what keeps the controller's hit-test geometry in step with the layout between
   /// two frames.
@@ -277,10 +279,10 @@ class PlotArea {
   /// press capture, so a host may call it freely.
   input::Controller& controller_at(f32 x, f32 y) noexcept;
 
-  /// The figure row a point in the widget's **logical** coordinates lands in -- the
+  /// The flattened plot index a point in the widget's **logical** coordinates lands in -- the
   /// coordinates every GTK event controller reports, so a host's own drop target or
-  /// context menu can name the row a pointer is over without converting anything. The
-  /// same nearest-row rule as `controller_at()`, and 0 while no figure is set.
+  /// context menu can name the plot a pointer is over without converting anything. The
+  /// same nearest-cell rule (x and y) as `controller_at()`, and 0 while no figure is set.
   u32 row_at(double x, double y) const noexcept;
 
   /// Re-reads the figure's row rects into the cache the event routing answers from --
@@ -376,20 +378,21 @@ class PlotArea {
   /// into device pixels. The one place that mapping exists.
   Vec2 to_device(double x, double y) const noexcept;
 
-  /// The controller one event of this area's goes to, given the event's device y.
+  /// The controller one event of this area's goes to, given the event's device (x, y).
   /// `controller_` while no figure is set; otherwise the row the gesture *belongs*
   /// to: the row the open press claimed while a press is open, and the row under `y`
-  /// between gestures. That is the capture `controller_at()` deliberately omits, and
+  /// between gestures (x and y pick the cell). That is the capture `controller_at()` deliberately omits, and
   /// it is why this -- not `controller_at()` -- is what every handler below calls.
   ///
   /// Hands the chosen row its own viewport, so the geometry it hit-tests is the
   /// geometry the last frame drew.
-  input::Controller& target_controller(f32 y) noexcept;
-  /// The row of `row_rects_` a device y belongs to: the row it is in, or the nearest
-  /// one when it is in none (a row gap, a margin outside the figure). Selection by
-  /// distance rather than "the first that matches" is what makes a pixel in a visible
-  /// gap belong to the row it is *near* instead of to row 0.
-  static u32 row_in(const std::vector<Rect>& rows, f32 y) noexcept;
+  input::Controller& target_controller(f32 x, f32 y) noexcept;
+  /// The cell of `row_rects_` (the figure's flattened cell rects) a device pixel belongs
+  /// to: the cell it is in, or the nearest one when it is in none (a row or column gap,
+  /// a margin outside the figure). Selection by distance rather than "the first that
+  /// matches" is what makes a pixel in a visible gap belong to the cell it is *near*
+  /// instead of to plot 0.
+  static u32 row_in(const std::vector<Rect>& rows, f32 x, f32 y) noexcept;
   /// The row this area's events currently go to: the press's row while one is open,
   /// so an in-flight gesture keeps its highlight, and the row under the last pointer
   /// position otherwise. 0 with no rows.
@@ -457,7 +460,8 @@ class PlotArea {
   /// `set_figure()` is called, and the single-plot path reads neither.
   Figure* figure_ = nullptr;
   std::vector<std::unique_ptr<input::Controller>> row_controllers_;
-  /// The figure's row rects as of the last `refresh_row_rects()`: the cache the event
+  /// The figure's cell rects (one per plot, flattened; the row rects when no row is split)
+  /// as of the last `refresh_row_rects()`: the cache the event
   /// routing reads instead of laying the figure out per event. Empty while no figure
   /// is set, which is the state the routing falls back to `controller_` on.
   std::vector<Rect> row_rects_;

include/plot/plot/figure.hpp

@@ -33,7 +33,9 @@ struct FigureLayout {
   /// cells, the cells' widths summing to the row's less the gaps.
   std::vector<Rect> cells;
   /// The strip the figure's one shared x axis is drawn in: the bottom row's own
-  /// `PlotLayout::x_label_area`, at the bottom of the bottom row's rect and so as
+  /// `PlotLayout::x_label_area` (for a bottom row split into several cells, only the **last
+  /// cell's** strip -- the others' strips are their own `plot(i).layout().x_label_area`, which
+  /// is where the controller's axis-zoom hit test reads each cell's gestures from), at the bottom of the bottom row's rect and so as
   /// wide as that row's axes rather than the whole figure. Read back from the row
   /// rather than derived here, so a host and the frame cannot disagree about where
   /// the axis is. It is nonzero whenever the figure has rows and the bottom row
@@ -236,17 +238,18 @@ class Figure {
   /// is not a number; such a call therefore leaves every row's crosshair as it was.
   void set_crosshair(f64 x, bool active);
 
-  /// Places the crosshair with the pointer's **row** and that row's local y (spec §17): the
-  /// shared x goes to every row -- vertical lines everywhere, as the plain overload does -- and
-  /// the horizontal line is drawn **only in `hovered_row`**, where its y is a value of *that*
-  /// row's own scale. It is the fix for the reported defect -- a figure showing no horizontal
+  /// Places the crosshair with the pointer's **plot** and that plot's local y (spec §17): the
+  /// shared x goes to every plot -- vertical lines everywhere, as the plain overload does -- and
+  /// the horizontal line is drawn **only in `hovered_row`** -- the **flattened plot index**, not
+  /// the figure-row index; they differ when a row holds several cells -- where its y is a value of
+  /// *that* plot's own scale. It is the fix for the reported defect -- a figure showing no horizontal
   /// line at all -- without inventing a figure-wide y, which would mean a different value in
   /// every row: the line appears where the pointer is, and no row ever shows another row's y.
   ///
   /// `y_in_row` is a data coordinate on `hovered_row`'s y axis 0, exactly as `Crosshair::y`'s
   /// two-coordinate placement is; a host reads it from the row's own y transform at the
-  /// pointer's pixel row. `hovered_row` outside `[0, row_count())` is treated as "no row under
-  /// the pointer": every row gets the vertical line and none gets a horizontal one, the same
+  /// pointer's pixel row. `hovered_row` outside `[0, plot_count())` is treated as "no plot under
+  /// the pointer": every plot gets the vertical line and none gets a horizontal one, the same
   /// state the single-coordinate overload produces.
   ///
   /// Refused, changing nothing, when `x` is not a number -- matching `set_crosshair(x, active)`
@@ -267,9 +270,10 @@ class Figure {
   /// How many groups there are, excluding the unlinked group 0.
   u32 x_link_count() const noexcept { return static_cast<u32>(links_.size()); }
 
-  /// Moves one row into a link group and applies that group's range to it at once,
-  /// so the row is on the group's window from this call rather than from the next
-  /// frame. `group` 0 takes the row back out of its group, leaving it with the range
+  /// Moves one plot into a link group and applies that group's range to it at once; `row`
+  /// is the **flattened plot index** (see `plot_count()`), which is the row index only for a
+  /// figure with one cell per row. The plot is on the group's window from this call rather
+  /// than from the next frame. `group` 0 takes the plot back out of its group, leaving it with the range
   /// it holds now.
   ///
   /// A group with no range yet -- one that no row and no `set_x_link_range()` has
@@ -283,7 +287,7 @@ class Figure {
   /// per-row window. `XFollow::Off` is the group's to set
   /// (`set_x_link_follow()`), not the axis'.
   Status link_x(u32 row, u32 group);
-  /// The group a row is in, or 0 when it is in none.
+  /// The group the plot with flattened index `row` is in, or 0 when it is in none.
   u32 x_link(u32 row) const noexcept;
 
   /// Sets a group's shared range and pushes it to every member.

tests/test_glfw_host.cpp

@@ -14,6 +14,9 @@
 #include <glfw/glfw_host.hpp>
 #include <plot/plot/figure.hpp>
 
+#include <span>
+#include <vector>
+
 namespace {
 
 /// A figure of `rows` rows over a known rect, with an x and a y axis in every row (so
@@ -315,3 +318,31 @@ PLOT_TEST(the_host_keeps_its_own_controller_while_no_figure_is_set) {
   PLOT_CHECK(host.row_controller(0u) == nullptr);
   PLOT_CHECK(&host.controller_at(10.0f, 10.0f) == &host.controller());
 }
+
+PLOT_TEST(glfw_host_routes_by_cell) {
+  // A figure of two rows, the first of one cell and the second of two side by side: the
+  // pointer's x as well as its y picks the plot, and the controllers are indexed by the
+  // flattened plot.
+  std::vector<plot::u32> cells{1, 2};
+  plot::Figure figure{std::span<const plot::u32>(cells)};
+  figure.set_viewport(plot::Rect{0, 0, 300, 600});
+  figure.set_col_gap(6.0f);
+  for (plot::u32 i = 0; i < 3; ++i) {
+    figure.plot(i).add_x_axis({"t", {0.0, 1.0}, false, plot::AxisPlace::Bottom, false});
+    figure.plot(i).add_y_axis({"v", {-1.0, 1.0}, false, plot::AxisPlace::Left, false});
+  }
+  plot::glfw::Host host;
+  host.set_figure(&figure);
+  const std::vector<plot::Rect> c = figure.layout().cells;
+  PLOT_CHECK(c.size() == 3u);
+  for (plot::u32 i = 0; i < 3; ++i) {
+    PLOT_CHECK(host.row_controller(i) != nullptr);
+    const double cx = c[i].x + c[i].w * 0.5, cy = c[i].y + c[i].h * 0.5;
+    PLOT_CHECK(&host.controller_at(static_cast<plot::f32>(cx), static_cast<plot::f32>(cy)) ==
+               host.row_controller(i));
+  }
+  PLOT_CHECK(host.row_controller(3u) == nullptr);
+  // in the column gap: the nearest cell wins
+  PLOT_CHECK(&host.controller_at(c[1].right() + 1.0f, c[1].y + 5.0f) == host.row_controller(1));
+  PLOT_CHECK(&host.controller_at(c[2].x - 1.0f, c[2].y + 5.0f) == host.row_controller(2));
+}