Fix bug that allowed alpha to go negative

ensemble/ctf/editor_tools.py

@@ -3,7 +3,7 @@
 
 from ensemble.ctf.piecewise import PiecewiseFunction
 from ensemble.ctf.utils import (FunctionUIAdapter, AlphaFunctionUIAdapter,
-                                ColorFunctionUIAdapter, clip_to_unit)
+                                ColorFunctionUIAdapter, clip, clip_to_unit)
 
 
 class ValueMapper(object):
@@ -94,9 +94,10 @@ def set_delta(self, value, delta_x, delta_y):
             value_at = self.function.value_at
             x_limits = tuple([value_at(i)[0] for i in (index-1, index+1)])
 
-        x_val = min(max(x_limits[0], start_value[0] + delta_x), x_limits[1])
-        new_value = (x_val, start_value[1] + delta_y)
-        self.function.update(index, new_value)
+        x = clip(start_value[0] + delta_x, x_limits)
+        y = clip_to_unit(start_value[1] + delta_y)
+
+        self.function.update(index, (x, y))
         self.function_updated = True
 
 
@@ -117,7 +118,7 @@ def set_delta(self, value, delta_x, delta_y):
             value_at = self.function.value_at
             x_limits = tuple([value_at(i)[0] for i in (index-1, index+1)])
 
-        x_pos = min(max(x_limits[0], start_value[0] + delta_x), x_limits[1])
+        x_pos = clip(start_value[0] + delta_x, x_limits)
         new_value = (x_pos,) + start_value[1:]
         self.function.update(index, new_value)
         self.function_updated = True

ensemble/ctf/tests/test_editor_tools.py

@@ -0,0 +1,54 @@
+from ensemble.ctf.editor import ALPHA_DEFAULT, create_function
+
+from ensemble.ctf.editor_tools import AlphaFunctionEditorTool
+
+
+def init_alpha_function_tool():
+    alpha_function = create_function(ALPHA_DEFAULT)
+    return AlphaFunctionEditorTool(function=alpha_function)
+
+
+def test_move_first_point():
+    # The first point in the alpha curve cannot move in the x-direction
+    tool = init_alpha_function_tool()
+
+    dy = 0.5  # Note the first point is at y = 0, so we need 0 < dy < 1
+    index = 0
+    init_position = tool.function.value_at(index)
+    tool.set_delta((index, init_position), 0.1, dy)
+
+    final_position = tool.function.value_at(index)
+    # The x-position is pinned
+    assert final_position[0] == init_position[0]
+    assert final_position[1] == (init_position[1] + dy)
+
+
+def test_move_last_point():
+    # The last point in the alpha curve cannot move in the x-direction
+    tool = init_alpha_function_tool()
+
+    dy = -0.5  # Note the last point is at y = 1, so we need 0 < dy < -1
+    index = tool.function.size() - 1
+    init_position = tool.function.value_at(index)
+    tool.set_delta((index, init_position), -0.1, dy)
+
+    final_position = tool.function.value_at(index)
+    # The x-position is pinned
+    assert final_position[0] == init_position[0]
+    assert final_position[1] == (init_position[1] + dy)
+
+
+def test_node_doesnt_move_below_zero():
+    tool = init_alpha_function_tool()
+
+    index = 1
+    middle_point = (0.5, 0)
+    tool.function.insert(middle_point)
+
+    assert tool.function.size() == 3
+    assert tool.function.value_at(index) == middle_point
+
+    eps = 0.001
+    tool.set_delta((index, middle_point), 0, -eps)
+
+    assert tool.function.value_at(index) == middle_point

ensemble/ctf/utils.py

@@ -32,7 +32,12 @@ def func(pos):
 
 
 def clip_to_unit(value):
-    return min(max(value, 0.0), 1.0)
+    return clip(value, (0.0, 1.0))
+
+
+def clip(value, limits):
+    v_min, v_max = limits
+    return min(max(value, v_min), v_max)
 
 
 def point_dist(pos0, pos1):