fix multi-profile

backend/nodes/multi_profile.py

@@ -5,7 +5,23 @@ from __future__ import annotations
 import numpy as np
 
 from backend.node_registry import register_node
-from backend.data_types import DataField, LineData
+from backend.data_types import DataField, LineData, datafield_to_uint8, encode_preview
+from backend.execution_context import emit_overlay
+
+
+def _blend_fields(field_a: DataField, field_b: DataField, alpha: float) -> np.ndarray:
+    """Render field A with field B overlaid at `alpha` opacity (0=A only, 1=B only)."""
+    a_rgb = datafield_to_uint8(field_a, field_a.colormap).astype(np.float32)
+    b_rgb = datafield_to_uint8(field_b, field_b.colormap).astype(np.float32)
+    wa = 1.0 - alpha
+    wb = alpha
+    if b_rgb.shape != a_rgb.shape:
+        h = min(a_rgb.shape[0], b_rgb.shape[0])
+        w = min(a_rgb.shape[1], b_rgb.shape[1])
+        canvas = a_rgb.copy()
+        canvas[:h, :w] = wa * a_rgb[:h, :w] + wb * b_rgb[:h, :w]
+        return canvas.astype(np.uint8)
+    return (wa * a_rgb + wb * b_rgb).astype(np.uint8)
 
 
 @register_node(display_name="Multiple Profiles")
@@ -19,11 +35,12 @@ class MultipleProfiles:
                 "row": ("INT", {"default": -1, "min": -1, "max": 10000, "step": 1}),
                 "direction": (["horizontal", "vertical"], {"default": "horizontal"}),
                 "mode": (["overlay", "mean", "difference"], {"default": "overlay"}),
+                "blend": ("FLOAT", {"default": 0.5, "min": 0.0, "max": 1.0, "step": 0.01, "slider": True}),
             }
         }
 
     OUTPUTS = (
-        ('LINE_DATA', 'profile'),
+        ('LINE', 'profile'),
     )
     FUNCTION = "process"
 
@@ -31,12 +48,14 @@ class MultipleProfiles:
         "Extract and compare line profiles from two fields. "
         "Row=-1 uses the center row/column. Modes: overlay returns field_a's "
         "profile, mean averages both, difference subtracts b from a. "
+        "The preview shows field A blended with field B and highlights the "
+        "row or column being sampled — drag to move the line."
     )
 
     KEYWORDS = ("line profile", "compare", "overlay", "cross section")
 
     def process(self, field_a: DataField, field_b: DataField,
-                row: int, direction: str, mode: str) -> tuple:
+                row: int, direction: str, mode: str, blend: float = 0.5) -> tuple:
         a = np.asarray(field_a.data, dtype=np.float64)
         b = np.asarray(field_b.data, dtype=np.float64)
 
@@ -49,6 +68,7 @@ class MultipleProfiles:
             pa = pa[:len(pb)]
             dx = field_a.dx
             x_unit = field_a.si_unit_xy
+            line_axis_max = a.shape[0] - 1
         else:
             if row < 0:
                 row = a.shape[1] // 2
@@ -58,6 +78,7 @@ class MultipleProfiles:
             pa = pa[:len(pb)]
             dx = field_a.dy
             x_unit = field_a.si_unit_xy
+            line_axis_max = a.shape[1] - 1
 
         x_axis = np.arange(len(pa)) * dx
 
@@ -70,5 +91,15 @@ class MultipleProfiles:
         else:
             result = pa
 
+        alpha = float(np.clip(blend, 0.0, 1.0))
+        emit_overlay({
+            "kind": "multi_profile",
+            "section_title": "Preview",
+            "image": encode_preview(_blend_fields(field_a, field_b, alpha)),
+            "row": int(row),
+            "direction": direction,
+            "max_index": int(line_axis_max),
+        })
+
         return (LineData(data=result, x_axis=x_axis, x_unit=x_unit,
                          y_unit=field_a.si_unit_z),)