feat(input): Ctrl restricts keyboard zoom to x, Alt to y

src/input/controller.cpp

@@ -323,17 +323,27 @@ void Controller::on_key(const KeyEvent& e) {
   if (zooms) {
     const f64 notches = e.key == kKeyZoomIn ? kKeyZoomNotches : -kKeyZoomNotches;
     const f64 factor = zoom_factor(notches);
-    for (u32 i = 0; i < plot_->x_axis_count(); ++i) {
-      const Axis& a = plot_->x_axis(i);
-      const f64 lo = to_space(a.range.min, a.log);
-      const f64 hi = to_space(a.range.max, a.log);
-      zoom_x_axis(i, from_space(0.5 * (lo + hi), a.log), factor);
+    // Ctrl restricts the zoom to x, Alt to y; bare +/- zooms both. (Shift cannot be
+    // used: '+' is shift+'=' on common layouts, so key_from() folds them together and
+    // a bare zoom-in already arrives with Mod::Shift set.) Ctrl+Alt zooms neither,
+    // which is harmless and needs no special case.
+    const bool only_x = has_mod(e.mods, Mod::Ctrl);
+    const bool only_y = has_mod(e.mods, Mod::Alt);
+    if (!only_y) {
+      for (u32 i = 0; i < plot_->x_axis_count(); ++i) {
+        const Axis& a = plot_->x_axis(i);
+        const f64 lo = to_space(a.range.min, a.log);
+        const f64 hi = to_space(a.range.max, a.log);
+        zoom_x_axis(i, from_space(0.5 * (lo + hi), a.log), factor);
+      }
     }
-    for (u32 i = 0; i < plot_->y_axis_count(); ++i) {
-      const Axis& a = plot_->y_axis(i);
-      const f64 lo = to_space(a.range.min, a.log);
-      const f64 hi = to_space(a.range.max, a.log);
-      zoom_y_axis(i, from_space(0.5 * (lo + hi), a.log), factor);
+    if (!only_x) {
+      for (u32 i = 0; i < plot_->y_axis_count(); ++i) {
+        const Axis& a = plot_->y_axis(i);
+        const f64 lo = to_space(a.range.min, a.log);
+        const f64 hi = to_space(a.range.max, a.log);
+        zoom_y_axis(i, from_space(0.5 * (lo + hi), a.log), factor);
+      }
     }
   } else if (fits) {
     plot_->auto_fit_x();