feat: waveform drag-select + wheel zoom (selection_changed/view_changed)

main.py

@@ -3943,6 +3943,13 @@ class AudioWaveform(QWidget):
     audio region. Populated on demand via manual refresh (no implicit UI-thread
     decode)."""
 
+    selection_changed = pyqtSignal(float, float)
+    view_changed = pyqtSignal(float, float)
+
+    HANDLE_PX = 6
+    MIN_SPAN = 0.05
+    MIN_SEL = 0.01
+
     def __init__(self, parent=None):
         super().__init__(parent)
         self._peaks: list[float] = []
@@ -3950,6 +3957,7 @@ class AudioWaveform(QWidget):
         self._view_dur = 0.0
         self._sel: tuple[float, float] | None = None
         self._playhead: float | None = None
+        self._drag_anchor: float | None = None
         self.setFixedHeight(96)
         self.setToolTip("Waveform of the current audio area (↻ to refresh)")
 
@@ -4011,6 +4019,82 @@ class AudioWaveform(QWidget):
             p.setPen(QPen(QColor(255, 255, 255, 160), 1))
             p.drawLine(px, 0, px, h)
 
+    # --- pixel/time helpers -------------------------------------------------
+    def _px_to_t(self, x: float) -> float:
+        from core.waveform import x_to_t
+        return x_to_t(x, self.width(), self._view_start, self._view_dur)
+
+    def _t_to_px(self, t: float) -> int:
+        from core.waveform import t_to_x
+        return t_to_x(t, self.width(), self._view_start, self._view_dur)
+
+    # --- drag-select / zoom -------------------------------------------------
+    def _begin_drag_at_x(self, x: float) -> None:
+        t = self._px_to_t(x)
+        anchor = t
+        if self._sel is not None and self._view_dur > 0:
+            xs = self._t_to_px(self._sel[0])
+            xe = self._t_to_px(self._sel[1])
+            if abs(x - xs) <= self.HANDLE_PX:
+                anchor = self._sel[1]      # drag start; pivot on end
+            elif abs(x - xe) <= self.HANDLE_PX:
+                anchor = self._sel[0]      # drag end; pivot on start
+        self._drag_anchor = anchor
+        self._drag_to_x(x)
+
+    def _drag_to_x(self, x: float) -> None:
+        if self._drag_anchor is None:
+            return
+        t = self._px_to_t(x)
+        lo, hi = min(self._drag_anchor, t), max(self._drag_anchor, t)
+        vs, ve = self._view_start, self._view_start + self._view_dur
+        if self._view_dur > 0:
+            lo = max(vs, min(lo, ve))
+            hi = max(vs, min(hi, ve))
+        if hi - lo < self.MIN_SEL:
+            if hi + self.MIN_SEL <= ve or self._view_dur <= 0:
+                hi = lo + self.MIN_SEL      # room above
+            else:
+                lo = hi - self.MIN_SEL      # at the ceiling -> grow downward
+        self.set_selection(lo, hi)
+
+    def _end_drag(self) -> None:
+        if self._drag_anchor is None:
+            return
+        self._drag_anchor = None
+        if self._sel is not None:
+            self.selection_changed.emit(self._sel[0], self._sel[1])
+
+    def _zoom_at_x(self, x: float, factor: float) -> None:
+        if self._view_dur <= 0 or self.width() <= 0:
+            return
+        t = self._px_to_t(x)
+        new_dur = max(self.MIN_SPAN, self._view_dur * factor)
+        frac = x / self.width()
+        self._view_start = t - frac * new_dur
+        self._view_dur = new_dur
+        self.update()
+        self.view_changed.emit(self._view_start, self._view_dur)
+
+    # --- Qt events ----------------------------------------------------------
+    def mousePressEvent(self, e):
+        if e.button() == Qt.MouseButton.LeftButton:
+            self._begin_drag_at_x(e.position().x())
+
+    def mouseMoveEvent(self, e):
+        self._drag_to_x(e.position().x())
+
+    def mouseReleaseEvent(self, e):
+        if e.button() == Qt.MouseButton.LeftButton:
+            self._end_drag()
+
+    def wheelEvent(self, e):
+        dy = e.angleDelta().y()
+        if dy == 0:
+            return
+        factor = 0.8 if dy > 0 else 1.25
+        self._zoom_at_x(e.position().x(), factor)
+
 
 class MainWindow(QMainWindow):
     def __init__(self):