Add example of rendering pointclouds with a background color.

Summary:
Add cells to the rendering_colored_points tutorial showing how to initialize a renderer and compositor that will render pointclouds with a background color.

{F333731292}
{F334136799}

Reviewed By: nikhilaravi

Differential Revision: D23632503

fbshipit-source-id: e9ce0178b41e74baf912bd82ca1db41b680fc68f

docs/tutorials/render_colored_points.ipynb

@@ -62,7 +62,7 @@
     "import matplotlib.pyplot as plt\n",
     "from skimage.io import imread\n",
     "\n",
-    "# Util function for loading point clouds\n",
+    "# Util function for loading point clouds|\n",
     "import numpy as np\n",
     "\n",
     "# Data structures and functions for rendering\n",
@@ -187,6 +187,32 @@
     "plt.axis(\"off\");"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "We will now modify the **renderer** to use **alpha compositing** with a set background color. "
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "renderer = PointsRenderer(\n",
+    "    rasterizer=PointsRasterizer(cameras=cameras, raster_settings=raster_settings),\n",
+    "    # Pass in background_color to the alpha compositor, setting the background color \n",
+    "    # to the 3 item tuple, representing rgb on a scale of 0 -> 1, in this case blue\n",
+    "    compositor=AlphaCompositor(background_color=(0, 0, 1))\n",
+    ")\n",
+    "images = renderer(point_cloud)\n",
+    "plt.figure(figsize=(10, 10))\n",
+    "plt.imshow(images[0, ..., :3].cpu().numpy())\n",
+    "plt.grid(\"off\")\n",
+    "plt.axis(\"off\");"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -234,6 +260,32 @@
     "plt.grid(\"off\")\n",
     "plt.axis(\"off\");"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "We will now modify the **renderer** to use **weighted compositing** with a set background color. "
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "renderer = PointsRenderer(\n",
+    "    rasterizer=PointsRasterizer(cameras=cameras, raster_settings=raster_settings),\n",
+    "    # Pass in background_color to the norm weighted compositor, setting the background color \n",
+    "    # to the 3 item tuple, representing rgb on a scale of 0 -> 1, in this case red\n",
+    "    compositor=NormWeightedCompositor(background_color=(1,0,0))\n",
+    ")\n",
+    "images = renderer(point_cloud)\n",
+    "plt.figure(figsize=(10, 10))\n",
+    "plt.imshow(images[0, ..., :3].cpu().numpy())\n",
+    "plt.grid(\"off\")\n",
+    "plt.axis(\"off\");"
+   ]
   }
  ],
  "metadata": {