Add composite color strip source type with layer blending

Composite sources stack multiple existing color strip sources as layers
with configurable blend modes (Normal, Add, Multiply, Screen) and per-layer
opacity. Includes full CRUD, hot-reload, delete protection for referenced
layers, and pre-allocated integer blend math at 30 FPS.

Also eliminates per-frame numpy allocations in color_strip_stream,
effect_stream, and wled_target_processor (buffer pre-allocation).

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

server/src/wled_controller/storage/color_strip_source.py

@@ -71,6 +71,7 @@ class ColorStripSource:
             "intensity": None,
             "scale": None,
             "mirror": None,
+            "layers": None,
         }
 
     @staticmethod
@@ -139,6 +140,14 @@ class ColorStripSource:
                 led_count=data.get("led_count") or 0,
             )
 
+        if source_type == "composite":
+            return CompositeColorStripSource(
+                id=sid, name=name, source_type="composite",
+                created_at=created_at, updated_at=updated_at, description=description,
+                layers=data.get("layers") or [],
+                led_count=data.get("led_count") or 0,
+            )
+
         if source_type == "effect":
             raw_color = data.get("color")
             color = (
@@ -317,3 +326,23 @@ class EffectColorStripSource(ColorStripSource):
         d["scale"] = self.scale
         d["mirror"] = self.mirror
         return d
+
+
+@dataclass
+class CompositeColorStripSource(ColorStripSource):
+    """Color strip source that composites (stacks) multiple other sources as layers.
+
+    Each layer references a non-composite ColorStripSource with blend mode and opacity.
+    Layers are blended bottom-to-top. LED count auto-sizes from the connected device
+    when led_count == 0.
+    """
+
+    # Each layer: {"source_id": str, "blend_mode": str, "opacity": float, "enabled": bool}
+    layers: list = field(default_factory=list)
+    led_count: int = 0  # 0 = use device LED count
+
+    def to_dict(self) -> dict:
+        d = super().to_dict()
+        d["layers"] = [dict(layer) for layer in self.layers]
+        d["led_count"] = self.led_count
+        return d

server/src/wled_controller/storage/color_strip_store.py

@@ -10,6 +10,7 @@ from wled_controller.core.capture.calibration import CalibrationConfig, calibrat
 from wled_controller.storage.color_strip_source import (
     ColorCycleColorStripSource,
     ColorStripSource,
+    CompositeColorStripSource,
     EffectColorStripSource,
     GradientColorStripSource,
     PictureColorStripSource,
@@ -116,6 +117,7 @@ class ColorStripStore:
         intensity: float = 1.0,
         scale: float = 1.0,
         mirror: bool = False,
+        layers: Optional[list] = None,
     ) -> ColorStripSource:
         """Create a new color strip source.
 
@@ -194,6 +196,17 @@ class ColorStripStore:
                 scale=float(scale) if scale else 1.0,
                 mirror=bool(mirror),
             )
+        elif source_type == "composite":
+            source = CompositeColorStripSource(
+                id=source_id,
+                name=name,
+                source_type="composite",
+                created_at=now,
+                updated_at=now,
+                description=description,
+                layers=layers if isinstance(layers, list) else [],
+                led_count=led_count,
+            )
         else:
             if calibration is None:
                 calibration = CalibrationConfig(layout="clockwise", start_position="bottom_left")
@@ -248,6 +261,7 @@ class ColorStripStore:
         intensity: Optional[float] = None,
         scale: Optional[float] = None,
         mirror: Optional[bool] = None,
+        layers: Optional[list] = None,
     ) -> ColorStripSource:
         """Update an existing color strip source.
 
@@ -328,6 +342,11 @@ class ColorStripStore:
                 source.scale = float(scale)
             if mirror is not None:
                 source.mirror = bool(mirror)
+        elif isinstance(source, CompositeColorStripSource):
+            if layers is not None and isinstance(layers, list):
+                source.layers = layers
+            if led_count is not None:
+                source.led_count = led_count
 
         source.updated_at = datetime.utcnow()
         self._save()
@@ -349,6 +368,15 @@ class ColorStripStore:
 
         logger.info(f"Deleted color strip source: {source_id}")
 
+    def is_referenced_by_composite(self, source_id: str) -> bool:
+        """Check if this source is referenced as a layer in any composite source."""
+        for source in self._sources.values():
+            if isinstance(source, CompositeColorStripSource):
+                for layer in source.layers:
+                    if layer.get("source_id") == source_id:
+                        return True
+        return False
+
     def is_referenced_by_target(self, source_id: str, target_store) -> bool:
         """Check if this source is referenced by any picture target."""
         from wled_controller.storage.wled_picture_target import WledPictureTarget