feat: Offer the Frame TV panel size as a crop preset

tests/test_crop_presets.py

@@ -0,0 +1,42 @@
+"""Covers the crop presets offered for a Frame TV panel.
+
+Run with: pytest tests/test_crop_presets.py
+"""
+
+import pytest
+from PIL import Image as PILImage
+
+from utils.crop_image import CROP_PRESETS, CropImageError, get_preset_crop_box
+
+
+@pytest.fixture
+def image(tmp_path):
+    def make(width, height):
+        path = tmp_path / f"{width}x{height}.png"
+        PILImage.new("RGB", (width, height), "red").save(path)
+        return str(path)
+    return make
+
+
+def test_the_frame_tv_panel_size_is_offered_as_a_preset():
+    assert CROP_PRESETS["3840x2160"]["width"] == 3840
+    assert CROP_PRESETS["3840x2160"]["height"] == 2160
+
+
+def test_the_4k_preset_takes_a_centred_panel_sized_crop(image):
+    x, y, width, height = get_preset_crop_box(image(4200, 2400), "3840x2160")
+
+    assert (width, height) == (3840, 2160), "exactly the panel, no rescaling on the TV"
+    assert x == (4200 - 3840) // 2 and y == (2400 - 2160) // 2, "centred"
+
+
+def test_a_source_smaller_than_the_panel_is_not_asked_for_more_than_it_has(image):
+    x, y, width, height = get_preset_crop_box(image(1600, 900), "3840x2160")
+
+    assert (x, y) == (0, 0)
+    assert (width, height) == (1600, 900), "the whole image, not a box past its edge"
+
+
+def test_an_unknown_preset_is_refused(image):
+    with pytest.raises(CropImageError):
+        get_preset_crop_box(image(4200, 2400), "not-a-preset")

utils/crop_image.py

@@ -21,6 +21,9 @@ class CropImageError(Exception):
     '1024x768': {'width': 1024, 'height': 768, 'label': '1024x768 (4:3)'},
     '1280x960': {'width': 1280, 'height': 960, 'label': '1280x960 (4:3)'},
     '1920x1080': {'width': 1920, 'height': 1080, 'label': '1920x1080 (16:9)'},
+    # A Frame TV reports resolution_type UHD, so this is the one that fills the panel
+    # without the set having to rescale.
+    '3840x2160': {'width': 3840, 'height': 2160, 'label': '3840x2160 (4K, Frame TV)'},
 }