Fix BaseXYPlot map_screen (#802)

* verify / adjust as needed input shape to map_screen. Also, return an empty array of correct shape instead of empty list in case of empty input

* fix use of map_screen in LinePlot to fix test failures

* make similar changes to subclasses

* add regression test

* similar updates for segment plot along with test

* flake8

* ErrorBarPlot is also a BaseXYPlot descendent

* fix hittest_tool.py with recent changes

chaco/base_xy_plot.py

@@ -11,7 +11,7 @@
 """ Defines the base class for XY plots.
 """
 from math import sqrt
-from numpy import around, array, isnan, transpose
+from numpy import around, array, empty, isnan, transpose
 
 # Enthought library imports
 from enable.api import black_color_trait
@@ -353,9 +353,16 @@ def map_screen(self, data_array):
 
         Implements the AbstractPlotRenderer interface.
         """
-        # data_array is Nx2 array
+        # ensure data_array is an N1 x ... Nk x 2 ndarray for some k >= 1
+        data_array = array(data_array)
+
+        if data_array.ndim == 1:
+            data_array = data_array.reshape(-1, 2)
+        if data_array.shape[-1] != 2:
+            raise ValueError("Input to map_screen must have shape (..., 2)")
+
         if len(data_array) == 0:
-            return []
+            return empty(shape=(0, 2))
 
         x_ary, y_ary = transpose(data_array)
 

chaco/examples/demo/basic/hittest_tool.py

@@ -46,7 +46,7 @@ def normal_mouse_move(self, event):
         else:
             x, y = self.component.map_data((y, x))
 
-        x, y = self.line_plot.map_screen((x, y))
+        x, y = self.line_plot.map_screen((x, y))[0]
         self.pt = self.line_plot.hittest((x, y), threshold=self.threshold)
         self.request_redraw()
 

chaco/plots/barplot.py

@@ -16,6 +16,7 @@
     array,
     compress,
     column_stack,
+    empty,
     invert,
     isnan,
     transpose,
@@ -176,9 +177,12 @@ def map_screen(self, data_array):
 
         Implements the AbstractPlotRenderer interface.
         """
+        # ensure data_array is an Nx2 ndarray
+        data_array = array(data_array)
+        data_array = data_array.reshape(-1,2)
         # data_array is Nx2 array
         if len(data_array) == 0:
-            return []
+            return empty(shape=(0,2))
         x_ary, y_ary = transpose(data_array)
         sx = self.index_mapper.map_screen(x_ary)
         sy = self.value_mapper.map_screen(y_ary)

chaco/plots/errorbar_plot.py

@@ -9,7 +9,7 @@
 # Thanks for using Enthought open source!
 
 # Major library imports
-from numpy import column_stack, compress, invert, isnan, transpose
+from numpy import column_stack, compress, empty, invert, isnan, transpose
 import logging
 
 # Enthought library imports
@@ -49,7 +49,7 @@ def map_screen(self, data_array):
         or (y, xlow, xhigh) depending on self.orientation.
         """
         if len(data_array) == 0:
-            return []
+            return empty(shape=(0, 2))
         elif data_array.shape[1] == 2:
             return LinePlot.map_screen(self, data_array)
         else:

chaco/plots/lineplot.py

@@ -122,7 +122,7 @@ def hittest(self, screen_pt, threshold=7.0, return_distance=False):
             # screen_pt is one of the points in the lineplot
             data_pt = (self.index.get_data()[ndx], self.value.get_data()[ndx])
             if return_distance:
-                scrn_pt = self.map_screen(data_pt)
+                scrn_pt = self.map_screen(data_pt)[0]
                 dist = sqrt(
                     (screen_pt[0] - scrn_pt[0]) ** 2
                     + (screen_pt[1] - scrn_pt[1]) ** 2

chaco/plots/scatterplot.py

@@ -21,6 +21,7 @@
     array,
     asarray,
     column_stack,
+    empty,
     isfinite,
     isnan,
     nanargmin,
@@ -299,7 +300,7 @@ def map_screen(self, data_array):
         """
         # data_array is Nx2 array
         if len(data_array) == 0:
-            return []
+            return empty(shape=(0,2))
 
         data_array = asarray(data_array)
         if len(data_array.shape) == 1:

chaco/plots/segment_plot.py

@@ -142,6 +142,27 @@ def hittest(self, *args, **kwargs):
     def map_index(self, *args, **kwargs):
         raise NotImplementedError()
 
+    def map_screen(self, data_array):
+        """Maps an Nx2x2 array of data points into screen space and returns it
+        as an array.
+        Implements the AbstractPlotRenderer interface.
+        """
+        # ensure data_array is an Nx2x2 ndarray
+        data_array = np.asarray(data_array)
+        data_array = data_array.reshape(-1, 2, 2)
+
+        if len(data_array) == 0:
+            return np.empty(shape=(0, 2, 2))
+
+        x_ary, y_ary = np.transpose(data_array)
+
+        sx = self.index_mapper.map_screen(x_ary)
+        sy = self.value_mapper.map_screen(y_ary)
+        if self.orientation == "h":
+            return np.transpose(np.array((sx, sy)))
+        else:
+            return np.transpose(np.array((sy, sx)))
+
     def _gather_points(self):
         """Collects the data points that are within the bounds of the plot and
         caches them.

chaco/tests/test_plot.py

@@ -10,6 +10,7 @@
 
 import unittest
 
+import numpy as np
 from numpy import alltrue, arange, array
 
 from enable.api import ComponentEditor
@@ -95,6 +96,18 @@ def test_segment_plot_color_width(self):
         actual = gc.bmp_array[:, :, :]
         self.assertFalse(alltrue(actual == 255))
 
+    def test_segment_plot_map_screen(self):
+        x = arange(10)
+        y = arange(1, 11)
+        data = ArrayPlotData(x=x, y=y)
+        plot = Plot(data)
+        plot_renderer = plot.plot(("x", "y"), "segment")[0]
+
+        screen_point = plot_renderer.map_screen([(0, 1), (1, 2)])
+
+        self.assertEqual(type(screen_point), np.ndarray)
+        self.assertEqual(screen_point.shape, (1, 2, 2))
+
     def test_text_plot(self):
         x = arange(10)
         y = arange(1, 11)
@@ -109,6 +122,30 @@ def test_text_plot(self):
         actual = gc.bmp_array[:, :, :]
         self.assertFalse(alltrue(actual == 255))
 
+    def check_map_screen(self, renderer):
+        arr = arange(10)
+        data = ArrayPlotData(x=arr, y=arr)
+        plot = Plot(data)
+        plot_renderer = plot.add_xy_plot(
+            'x', 'y', plot.renderer_map[renderer]
+        )[0]
+
+        screen_point = plot_renderer.map_screen((-1, 1))
+
+        self.assertEqual(type(screen_point), np.ndarray)
+        self.assertEqual(screen_point.shape, (1, 2))
+
+        screen_point = plot_renderer.map_screen([])
+
+        self.assertEqual(type(screen_point), np.ndarray)
+        self.assertEqual(screen_point.shape, (0, 2))
+
+    # serves as a regression test for enthought/chaco#272
+    def test_xy_plot_map_screen(self):
+        renderers = ["line", "scatter", "bar", "polygon"]
+        for renderer in renderers:
+            self.check_map_screen(renderer)
+
 
 class EmptyLinePlot(HasTraits):
     plot = Instance(Plot)