improved perfs and event management

src/plot_host.cpp

@@ -452,7 +452,19 @@ void RowSet::set_time_window(double seconds) {
     // `{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_});
+    // No edge to read: there are no samples bound yet, which is the state every structural
+    // change leaves behind -- a re-plan drops the rings' history, and this function is called
+    // from `apply_time_window()`, which is what re-plans. So this is not a rare fallback; it
+    // is the axis a mode change is drawn with until the first sample lands.
+    //
+    // Which is why it states the window the same way the branch above does, with its maximum
+    // *at* the edge the live view puts at x = 0. `{0, window}` -- what it asked for before --
+    // is an offset of a whole window by the rule the comment above states, so the frames
+    // between the re-plan and the first sample drew the time base one screen to the left of
+    // where the following frames drew it. Two or three frames, every time an event or a
+    // waveform was opened: a trace that jumps a screen sideways and comes back is the
+    // "the time base flickers and it is unusable" report.
+    figure_->set_x_link_range(x_group_, {-window_s_, 0.0});
   }
 }