Add support for custom reduce functions (#338)

* Add support for custom reducefn

* Add tutorial of custom reducefn

* Fix rendering in README

diffdrr/renderers.py

@@ -165,11 +165,16 @@ def _get_voxel(volume, xyzs, img, mode, align_corners):
     return img
 
 # %% ../notebooks/api/01_renderers.ipynb 9
+from typing import Callable
+
+
 def reduce(img, reducefn):
     if reducefn == "sum":
         return img.sum(dim=-1)
     elif reducefn == "max":
         return img.max(dim=-1).values
+    elif isinstance(reducefn, Callable):
+        return reducefn(img)
     else:
         raise ValueError(f"Only supports reducefn 'sum' or 'max', not {reducefn}")
 

notebooks/api/01_renderers.ipynb

@@ -279,11 +279,16 @@
    "outputs": [],
    "source": [
     "#| exporti\n",
+    "from typing import Callable\n",
+    "\n",
+    "\n",
     "def reduce(img, reducefn):\n",
     "    if reducefn == \"sum\":\n",
     "        return img.sum(dim=-1)\n",
     "    elif reducefn == \"max\":\n",
     "        return img.max(dim=-1).values\n",
+    "    elif isinstance(reducefn, Callable):\n",
+    "        return reducefn(img)\n",
     "    else:\n",
     "        raise ValueError(f\"Only supports reducefn 'sum' or 'max', not {reducefn}\")"
    ]