add basic screenshot functionality to RenderableWidget

for now screenshot data is stored in self.screenshot_data
self.screenshot_ready indicates that RenderableView has returned the image

Author: Isaak Lim

js/src/_base/Renderable.js

@@ -336,6 +336,14 @@ var RenderableView = widgets.DOMWidgetView.extend({
 
     },
 
+    screenshot: function() {
+        var data_url = this.renderer.domElement.toDataURL('image/png');
+        this.send({
+            type: 'screenshot',
+            ret_val: data_url,
+        });
+    },
+
     teardownViewer: function() {
 
         this.$renderer.off('mouseenter');
@@ -380,6 +388,9 @@ var RenderableView = widgets.DOMWidgetView.extend({
         case 'freeze':
             this.freeze();
             break;
+        case 'screenshot':
+            this.screenshot();
+            break;
         default:
         }
     },

pythreejs/_base/renderable.py

@@ -9,6 +9,13 @@
 from ..math.Plane_autogen import Plane
 from ..renderers.webgl.WebGLShadowMap_autogen import WebGLShadowMap
 
+import base64
+try:
+    from io import BytesIO as StringIO
+except:
+    from cStringIO import StringIO
+import PIL.Image
+
 
 class RenderableWidget(DOMWidget):
     _view_module = Unicode(npm_pkg_name).tag(sync=True)
@@ -42,6 +49,23 @@ class RenderableWidget(DOMWidget):
     clearColor = Unicode('#000000').tag(sync=True)
     clearOpacity = CFloat(1.0).tag(sync=True)
 
+    def __init__(self, **kwargs):
+        super(RenderableWidget, self).__init__(**kwargs)
+        self.on_msg(self._on_potential_ret_val)
+        self.screenshot_data = None
+        self.screenshot_ready = False
+
+    def _on_potential_ret_val(self, widget, content, buffers):
+        """Message callback used internally"""
+        if content['type'] == "screenshot":
+            self._handle_screenshot(content['ret_val'])
+
+    def _handle_screenshot(self, data):
+        data = data[data.find(',')+1:]
+        data = base64.b64decode(data)
+        self.screenshot_data = PIL.Image.open(StringIO(data))
+        self.screenshot_ready = True
+
     def send_msg(self, message_type, payload=None):
         if payload is None:
             payload = {}
@@ -64,6 +88,13 @@ def freeze(self):
         }
         self.send(content)
 
+    def screenshot(self):
+        self.screenshot_ready = False
+        content = {
+            "type": "screenshot"
+        }
+        self.send(content)
+
 
 class Preview(RenderableWidget):
     # renderer properties