Fix page counter visibility on pages with borders (issue #58)

cdisplayagain.py

@@ -1302,14 +1302,48 @@ def _page_counter_text(self) -> str | None:
         return f"{self._current_index + 1}/{total}"
 
     def _page_counter_color(self) -> str:
-        """Pick black or white text based on the mean luminance of the current page."""
+        """Pick black or white text based on the luminance of the page area where the counter sits.
+
+        The counter is drawn at the bottom-right of the canvas. Sample that region
+        (after accounting for image scaling/positioning) so the text contrasts with
+        whatever is actually behind it.
+        """
         if self._current_pil is None:
             return "#ffffff"
         try:
             from PIL import ImageStat
 
-            thumb = self._current_pil.convert("L").resize((32, 32), Image.Resampling.BILINEAR)
-            mean = ImageStat.Stat(thumb).mean[0]
+            cw = max(1, self.canvas.winfo_width())
+            ch = max(1, self.canvas.winfo_height())
+            if self._scaled_size is None:
+                thumb = self._current_pil.convert("L").resize((32, 32), Image.Resampling.BILINEAR)
+                mean = ImageStat.Stat(thumb).mean[0]
+                return "#000000" if mean >= 128 else "#ffffff"
+
+            iw, ih = self._scaled_size
+            margin = 12
+            cx = cw - margin
+            cy = ch - margin
+
+            image_left = (cw - iw) // 2
+            image_top = (ch - ih) // 2 if ih <= ch else -self._scroll_offset
+            img_x = max(0, min(iw - 1, cx - image_left))
+            img_y = max(0, min(ih - 1, cy - image_top))
+
+            sample_size = min(32, iw // 4, ih // 4)
+            if sample_size < 4:
+                sample_size = min(4, iw, ih)
+            left = max(0, img_x - sample_size)
+            top = max(0, img_y - sample_size)
+            right = min(iw, img_x + sample_size)
+            bottom = min(ih, img_y + sample_size)
+
+            if left >= right or top >= bottom:
+                thumb = self._current_pil.convert("L").resize((32, 32), Image.Resampling.BILINEAR)
+                mean = ImageStat.Stat(thumb).mean[0]
+            else:
+                region = self._current_pil.crop((left, top, right, bottom)).convert("L")
+                mean = ImageStat.Stat(region).mean[0]
         except Exception:
             return "#ffffff"
         return "#000000" if mean >= 128 else "#ffffff"

tests/test_page_counter.py

@@ -316,3 +316,77 @@ def test_render_current_sync_no_source_clears_counter(tk_root, tmp_path):
 
     viewer._render_current_sync()
     assert viewer._page_counter_id is None
+
+
+def test_counter_color_sampling_logic():
+    """Test the coordinate sampling logic directly."""
+    from PIL import Image, ImageStat
+
+    def test_sampling(img, cw, ch, iw, ih, scroll_offset=0):
+        """Test sampling logic for given image and dimensions."""
+        margin = 12
+        cx = cw - margin
+        cy = ch - margin
+
+        image_left = (cw - iw) // 2
+        image_top = (ch - ih) // 2 if ih <= ch else -scroll_offset
+        img_x = max(0, min(iw - 1, cx - image_left))
+        img_y = max(0, min(ih - 1, cy - image_top))
+
+        sample_size = min(32, iw // 4, ih // 4)
+        if sample_size < 4:
+            sample_size = min(4, iw, ih)
+        left = max(0, img_x - sample_size)
+        top = max(0, img_y - sample_size)
+        right = min(iw, img_x + sample_size)
+        bottom = min(ih, img_y + sample_size)
+
+        region = img.crop((left, top, right, bottom)).convert("L")
+        return ImageStat.Stat(region).mean[0]
+
+    # Test 1: Normal size image (fits in canvas)
+    # Create a dark page (100x100) with a white border in the bottom-right
+    img1 = Image.new("RGB", (100, 100), color=(0, 0, 0))
+    # Add white border in bottom-right 30x30 area
+    for x in range(70, 100):
+        for y in range(70, 100):
+            img1.putpixel((x, y), (255, 255, 255))
+
+    # Test with realistic canvas size
+    cw, ch = 800, 600
+    iw, ih = 100, 100
+    mean1 = test_sampling(img1, cw, ch, iw, ih)
+
+    # The counter area should be white, so text should be black
+    assert mean1 >= 128  # white area
+
+    # Test 2: Light page with dark border
+    img2 = Image.new("RGB", (100, 100), color=(255, 255, 255))
+    # Add dark border in bottom-right 30x30 area
+    for x in range(70, 100):
+        for y in range(70, 100):
+            img2.putpixel((x, y), (0, 0, 0))
+
+    mean2 = test_sampling(img2, cw, ch, iw, ih)
+    # The counter area should be dark, so text should be white
+    assert mean2 < 128  # dark area
+
+    # Test 3: Tall image (doesn't fit in canvas) - regression test for issue #58
+    # Create a tall dark page (100x1200) with white border at the bottom
+    img3 = Image.new("RGB", (100, 1200), color=(0, 0, 0))
+    # Add white border in bottom 30 rows
+    for x in range(0, 100):
+        for y in range(1170, 1200):
+            img3.putpixel((x, y), (255, 255, 255))
+
+    # Test with scroll offset = 0 (showing top of image)
+    cw, ch = 800, 600
+    iw, ih = 100, 1200
+    mean3 = test_sampling(img3, cw, ch, iw, ih, scroll_offset=0)
+    # Counter is at bottom of canvas, but we're showing top of image, so it should be dark
+    assert mean3 < 128  # dark area
+
+    # Test with scroll offset = 600 (showing bottom of image)
+    mean4 = test_sampling(img3, cw, ch, iw, ih, scroll_offset=600)
+    # Counter is at bottom of canvas, showing bottom of image, so it should be white
+    assert mean4 >= 128  # white area