Improve Channels window: split layout + derivative w.r.t. selector

- Split PipelineTab into Physical/Virtual sections via QSplitter
- Each section has independent scroll area, header, and add controls
- Add "With Respect To" control for derivative/second_derivative virtual channels: Time (dy/dt) or Channel (dy/dx)
- When Channel selected, x variable picker appears for any physical or derived channel
- signal_processor computes dy/dx using channel inputs when deriv_wrt=channel

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 35 insertions, 18 deletions

diff --git a/core/signal_processor.py b/core/signal_processor.py
index 723de66..df80dbb 100644
--- a/core/signal_processor.py
+++ b/core/signal_processor.py
@@ -442,28 +442,45 @@ class SignalProcessor(QObject):
             return dc._fn(inputs, t)
 
         elif dc.kind == "derivative":
-            # derivative of source[0]
-            src = dc.sources[0] if dc.sources else None
-            if src is None: return None
+            if not dc.sources: return None
             state = dc.params.setdefault("_state", {})
-            prev_t = state.get("t"); prev_v = state.get("v")
-            state["t"] = t; state["v"] = inputs[0]
-            if prev_t is None or t == prev_t: return 0.0
-            return (inputs[0] - prev_v) / (t - prev_t)
+            prev_v = state.get("v")
+            state["v"] = inputs[0]
+            if dc.params.get("deriv_wrt") == "channel":
+                if len(inputs) < 2: return None
+                prev_x = state.get("x")
+                state["x"] = inputs[1]
+                if prev_x is None or inputs[1] == prev_x: return 0.0
+                return (inputs[0] - prev_v) / (inputs[1] - prev_x)
+            else:
+                prev_t = state.get("t")
+                state["t"] = t
+                if prev_t is None or t == prev_t: return 0.0
+                return (inputs[0] - prev_v) / (t - prev_t)
 
         elif dc.kind == "second_derivative":
-            # second derivative — derivative of derivative
-            src = dc.sources[0] if dc.sources else None
-            if src is None: return None
+            if not dc.sources: return None
             state = dc.params.setdefault("_state", {})
-            prev_t = state.get("t"); prev_v = state.get("v")
-            cur_vel = 0.0
-            if prev_t is not None and t != prev_t:
-                cur_vel = (inputs[0] - prev_v) / (t - prev_t)
-            prev_vel = state.get("vel", 0.0)
-            state["t"] = t; state["v"] = inputs[0]; state["vel"] = cur_vel
-            if prev_t is None or t == prev_t: return 0.0
-            return (cur_vel - prev_vel) / (t - prev_t)
+            prev_v = state.get("v")
+            if dc.params.get("deriv_wrt") == "channel":
+                if len(inputs) < 2: return None
+                prev_x = state.get("x")
+                cur_vel = 0.0
+                if prev_x is not None and inputs[1] != prev_x:
+                    cur_vel = (inputs[0] - prev_v) / (inputs[1] - prev_x)
+                prev_vel = state.get("vel", 0.0)
+                state["x"] = inputs[1]; state["v"] = inputs[0]; state["vel"] = cur_vel
+                if prev_x is None or inputs[1] == prev_x: return 0.0
+                return (cur_vel - prev_vel) / (inputs[1] - prev_x)
+            else:
+                prev_t = state.get("t")
+                cur_vel = 0.0
+                if prev_t is not None and t != prev_t:
+                    cur_vel = (inputs[0] - prev_v) / (t - prev_t)
+                prev_vel = state.get("vel", 0.0)
+                state["t"] = t; state["v"] = inputs[0]; state["vel"] = cur_vel
+                if prev_t is None or t == prev_t: return 0.0
+                return (cur_vel - prev_vel) / (t - prev_t)
 
         elif dc.kind == "power":
             # V * I