Opacity example + missing import

Author: martinRenou

examples/introduction.ipynb

@@ -51,6 +51,7 @@
    "outputs": [],
    "source": [
     "c = ipycanvas.Canvas(stroke_style='red', size=(700, 200))\n",
+    "c.layout.width = '700px'\n",
     "c.layout.height = '200px'\n",
     "\n",
     "c"
@@ -207,7 +208,40 @@
    "execution_count": null,
    "metadata": {},
    "outputs": [],
-   "source": []
+   "source": [
+    "c = ipycanvas.Canvas(size=(150, 150))\n",
+    "c.layout.width = '150px'\n",
+    "c.layout.height = '150px'\n",
+    "\n",
+    "c"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Draw background\n",
+    "c.fill_style = '#FD0'\n",
+    "c.fill_rect(0, 0, 75, 75)\n",
+    "c.fill_style = '#6C0'\n",
+    "c.fill_rect(75, 0, 75, 75)\n",
+    "c.fill_style = '#09F'\n",
+    "c.fill_rect(0, 75, 75, 75)\n",
+    "c.fill_style = '#F30'\n",
+    "c.fill_rect(75, 75, 75, 75)\n",
+    "c.fill_style = '#FFF'\n",
+    "\n",
+    "# Set transparency value\n",
+    "c.global_alpha = 0.2;\n",
+    "\n",
+    "# Draw semi transparent circles\n",
+    "for i in range(7):\n",
+    "    c.begin_path();\n",
+    "    c.arc(75, 75, 10 + 10 * i, 0, pi * 2, True);\n",
+    "    c.fill();"
+   ]
   }
  ],
  "metadata": {

ipycanvas/canvas.py

@@ -6,7 +6,7 @@
 
 from ipywidgets import Color, DOMWidget
 
-from traitlets import Tuple, Unicode
+from traitlets import Float, Tuple, Unicode
 
 from ._frontend import module_name, module_version