Update color texture build to reduce collisions, and fix collision ha…

…ndling (#6182)

# Description

During work on #6179 I found that the mechanism for avoiding collision
does not work correctly (see tests). I also found that the shader code
do not have a stop condition.

In this PR, I also add a dynamic calculation of the hash table size. I
also decide to use prime numbers as the size of the table to reduce
collision probability.

---------

Co-authored-by: Juan Nunez-Iglesias <jni@fastmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Lorenzo Gaifas <brisvag@gmail.com>

examples/dev/direct-colormap-aliasing-test.py

@@ -56,7 +56,7 @@
 texel_pos_img = np.zeros((1, nb_steps, 4))
 texel_pos_img[..., -1] = 1  # alpha
 for k in range(nb_steps):
-    grid_position = hash2d_get(k + 1, keys, values)[0]
+    grid_position = hash2d_get(k + 1, keys)[0]
     # divide by shape and set to RG values like in shader (tex coords)
     texel_pos_img[:, k, :2] = (np.array(grid_position) + 0.5) / tex_shape
 

napari/_vispy/_tests/test_vispy_labels.py

@@ -0,0 +1,121 @@
+from itertools import product
+from unittest.mock import patch
+
+import numpy as np
+import pytest
+
+from napari._vispy.layers.labels import (
+    MAX_LOAD_FACTOR,
+    PRIME_NUM_TABLE,
+    build_textures_from_dict,
+    hash2d_get,
+    idx_to_2d,
+)
+
+
+@pytest.fixture(scope='module', autouse=True)
+def mock_max_texture_size():
+    """When running tests in this file, pretend max texture size is 2^16."""
+    with patch('napari._vispy.layers.labels.MAX_TEXTURE_SIZE', 2**16):
+        yield
+
+
+def test_idx_to_2d():
+    assert idx_to_2d(0, (100, 100)) == (0, 0)
+    assert idx_to_2d(1, (100, 100)) == (0, 1)
+    assert idx_to_2d(101, (100, 100)) == (1, 1)
+    assert idx_to_2d(521, (100, 100)) == (5, 21)
+    assert idx_to_2d(100 * 100 + 521, (100, 100)) == (5, 21)
+
+
+def test_build_textures_from_dict():
+    keys, values, collision = build_textures_from_dict(
+        {1: (1, 1, 1, 1), 2: (2, 2, 2, 2)}
+    )
+    assert not collision
+    assert keys.shape == (37, 37)
+    assert values.shape == (37, 37, 4)
+    assert keys[0, 1] == 1
+    assert keys[0, 2] == 2
+    assert np.array_equiv(values[0, 1], (1, 1, 1, 1))
+    assert np.array_equiv(values[0, 2], (2, 2, 2, 2))
+
+
+def test_build_textures_from_dict_too_many_labels(monkeypatch):
+    with pytest.raises(MemoryError):
+        build_textures_from_dict(
+            {i: (i, i, i, i) for i in range(1001)}, shape=(10, 10)
+        )
+    monkeypatch.setattr(
+        "napari._vispy.layers.labels.PRIME_NUM_TABLE", [[61], [127]]
+    )
+    with pytest.raises(MemoryError):
+        build_textures_from_dict(
+            {i: (i, i, i, i) for i in range((251**2) // 2)},
+        )
+
+
+def test_size_of_texture_square():
+    count = int(127 * 127 * MAX_LOAD_FACTOR) - 1
+    keys, values, *_ = build_textures_from_dict(
+        {i: (i, i, i, i) for i in range(count)}
+    )
+    assert keys.shape == (127, 127)
+    assert values.shape == (127, 127, 4)
+
+
+def test_size_of_texture_rectangle():
+    count = int(128 * 128 * MAX_LOAD_FACTOR) + 5
+    keys, values, *_ = build_textures_from_dict(
+        {i: (i, i, i, i) for i in range(count)}
+    )
+    assert keys.shape == (251, 127)
+    assert values.shape == (251, 127, 4)
+
+
+def test_build_textures_from_dict_collision():
+    keys, values, collision = build_textures_from_dict(
+        {1: (1, 1, 1, 1), 26: (2, 2, 2, 2), 27: (3, 3, 3, 3)}, shape=(5, 5)
+    )
+    assert collision
+    assert keys.shape == (5, 5)
+    assert keys[0, 1] == 1
+    assert keys[0, 2] == 26
+    assert keys[0, 3] == 27
+    assert np.array_equiv(values[0, 1], (1, 1, 1, 1))
+    assert np.array_equiv(values[0, 2], (2, 2, 2, 2))
+    assert np.array_equiv(values[0, 3], (3, 3, 3, 3))
+
+    assert hash2d_get(1, keys) == (0, 1)
+    assert hash2d_get(26, keys) == (0, 2)
+    assert hash2d_get(27, keys) == (0, 3)
+
+
+def test_collide_keys():
+    base_keys = [x * y for x, y in product(PRIME_NUM_TABLE[0], repeat=2)]
+    colors = {0: (0, 0, 0, 0), 1: (1, 1, 1, 1)}
+    colors.update({i + 10: (1, 0, 0, 1) for i in base_keys})
+    colors.update({2 * i + 10: (0, 1, 0, 1) for i in base_keys})
+    keys, values, collision = build_textures_from_dict(colors)
+    assert not collision
+    assert keys.shape == (37, 61)
+    assert values.shape == (37, 61, 4)
+
+
+def test_collide_keys2():
+    base_keys = [x * y for x, y in product(PRIME_NUM_TABLE[0], repeat=2)] + [
+        x * y for x, y in product(PRIME_NUM_TABLE[0], PRIME_NUM_TABLE[1])
+    ]
+    colors = {0: (0, 0, 0, 0), 1: (1, 1, 1, 1)}
+    colors.update({i + 10: (1, 0, 0, 1) for i in base_keys})
+    colors.update({2 * i + 10: (0, 1, 0, 1) for i in base_keys})
+
+    # enforce collision for collision table of size 31
+    colors.update({31 * i + 10: (0, 0, 1, 1) for i in base_keys})
+    # enforce collision for collision table of size 29
+    colors.update({29 * i + 10: (0, 0, 1, 1) for i in base_keys})
+
+    keys, values, collision = build_textures_from_dict(colors)
+    assert collision
+    assert keys.shape == (37, 37)
+    assert values.shape == (37, 37, 4)

napari/_vispy/layers/image.py

@@ -167,7 +167,7 @@ def _on_depiction_change(self):
         if isinstance(self.node, VolumeNode):
             self.node.raycasting_mode = str(self.layer.depiction)
 
-    def _on_colormap_change(self):
+    def _on_colormap_change(self, event=None):
         self.node.cmap = VispyColormap(*self.layer.colormap)
 
     def _update_mip_minip_cutoff(self):