Optimize lasso selection with a bounding box pre filter.

To optimize selection on scene with lot of vertices, bounding box filtering
is first done then polygon selection is done on remaining vertices.
At the very end mask are being recombined to have a selection mask over all vertices.

examples/scene/lasso.py

@@ -13,7 +13,6 @@
 The lasso selection is done on a 2D scatter but could be extended further by user.
 """
 import sys
-import time
 import numpy as np
 from vispy import app, scene
 from vispy.geometry import curves
@@ -25,7 +24,7 @@
 SELECTED_COLOR            = (0.3, 0, 1, 1.0)
 PEN_RADIUS                = 2
 MIN_MOVE_UPDATE_THRESHOLD = 5
-NUMBER_POINT              = 200000
+NUMBER_POINT              = 2000000
 SCATTER_SIZE              = 5
 
 canvas = scene.SceneCanvas(keys='interactive', show=True)
@@ -64,9 +63,20 @@ def points_in_polygon(polygon, pts):
     to add other dependencies, and your performance needs one of the other answers
     on the above question would serve you better (ex. shapely, etc).
     """
+    # Filter vertices out of the polygon's bounding box, this serve as an early optimization whenever number of vertices
+    # to filter out is huge.
+    x1, x2, y1, y2 = min(polygon[:, 0]), max(polygon[:, 0]), min(polygon[:, 1]), max(polygon[:, 1])
+    selection_mask = (x1 < pts[:, 0]) & (pts[:, 0] < x2) & (y1 < pts[:, 1]) & (pts[:, 1] < y2)
+    pts_in_bbox = pts[selection_mask]
+
+    # Select vertices inside the polygon.
     polygon = path.Path(polygon[:, :2], closed = True)
-    mask = polygon.contains_points(pts[:, :2])
-    return mask
+    polygon_mask    = polygon.contains_points(pts_in_bbox[:, :2]) 
+
+    # Return the full selection mask based on bounding box & polygon selection.
+    selection_mask[np.where(selection_mask == True)] &= polygon_mask
+
+    return selection_mask
 
 def select(polygon_vertices, points):
     # Set default mask to filter everything since user selection