regression test: Javascript buttons maskieren beim visuellen vergleich

Neue konstante Maskenrechtecke in PDF-Punktkoordinaten für die beiden Buttons unten rechts.
Neue Hilfsfunktion _mask_ignored_regions(...), die diese Bereiche auf Schwarz setzt.
Anwendung der Maske auf Seite 1 vor der Similarity-Berechnung.
Anwendung derselben maskierten Bilder auch für gespeicherte Diff-Bilder.

tests/test_regression.py

@@ -50,6 +50,13 @@ FIXTURES_DIR = Path(__file__).parent / "fixtures"
 SIMILARITY_THRESHOLD = 1.00   # minimum fraction of matching pixels per page
 PIXEL_TOLERANCE = 5           # max per-channel delta still counted as "same"
 RENDER_DPI = 150              # rendering resolution for PDF → image
+PAGE_WIDTH_PTS = 595.2760009765625
+PAGE_HEIGHT_PTS = 841.8900146484375
+# Ignore rendering differences for two JS-driven button widgets (bottom-right).
+IGNORE_RECTS_PTS = [
+    (457.8450012207031, 745.5402221679688, 563.4010009765625, 765.5402221679688),
+    (457.8450012207031, 767.4678955078125, 563.4010009765625, 786.35693359375),
+]
 
 
 # ---------------------------------------------------------------------------
@@ -136,6 +143,24 @@ def _resize_to_match(img: np.ndarray, target_shape: tuple) -> np.ndarray:
     return np.array(pil)
 
 
+def _mask_ignored_regions(img: np.ndarray) -> np.ndarray:
+    """Return a copy of *img* where ignored regions are blacked out."""
+    masked = img.copy()
+    h, w = masked.shape[:2]
+    scale_x = w / PAGE_WIDTH_PTS
+    scale_y = h / PAGE_HEIGHT_PTS
+
+    for x0_pt, y0_pt, x1_pt, y1_pt in IGNORE_RECTS_PTS:
+        x0 = max(0, min(w, int(round(x0_pt * scale_x))))
+        y0 = max(0, min(h, int(round(y0_pt * scale_y))))
+        x1 = max(0, min(w, int(round(x1_pt * scale_x))))
+        y1 = max(0, min(h, int(round(y1_pt * scale_y))))
+        if x1 > x0 and y1 > y0:
+            masked[y0:y1, x0:x1] = 0
+
+    return masked
+
+
 def _compute_similarity(ref: np.ndarray, gen: np.ndarray) -> float:
     """Return the fraction of pixels where all RGB channels differ by at most PIXEL_TOLERANCE."""
     if ref.shape != gen.shape:
@@ -249,13 +274,21 @@ def test_pdf_matches_reference(
                 failures.append(f"  {page_label}: Seite fehlt in generierter PDF.")
                 continue
 
-            similarity = _compute_similarity(ref_images[page_idx], gen_images[page_idx])
+            ref_img = ref_images[page_idx]
+            gen_img = gen_images[page_idx]
+
+            # Ignore the two bottom-right JavaScript button regions on page 1.
+            if page_idx == 0:
+                ref_img = _mask_ignored_regions(ref_img)
+                gen_img = _mask_ignored_regions(gen_img)
+
+            similarity = _compute_similarity(ref_img, gen_img)
 
             if similarity < SIMILARITY_THRESHOLD:
                 page_tag = f"seite_{page_idx + 1:02d}"
                 img_dir = diff_dir / clean_stem / page_tag
                 _save_diff_images(
-                    ref_images[page_idx], gen_images[page_idx], img_dir, page_tag
+                    ref_img, gen_img, img_dir, page_tag
                 )
                 rel = img_dir.relative_to(project_root)
                 failures.append(