Precise Seam: new full-coverage policy for Seam Blocked (#16170)

* Precise Seam: new full-coverage policy for Seam Blocked

A Seam Blocked modifier that covers a whole perimeter now blocks it, like a
perimeter painted red all round, instead of being skipped. It overrides
painting and lower-priority modifiers, like Enforced and Neutral. A new
warning names the modifier: "Seam Blocked modifier "<name>" of "<object>"
covers an entire perimeter". It is shown only when a perimeter stays
entirely Blocked after all weak modifiers. The full-containment warning now
covers only Center, Left and Right.

* Precise Seam: fix seams on perimeters blocked all round

- SeamComparator::is_first_not_much_worse() compares the types first, so two
  Blocked candidates fall through like Neutral ones. On a perimeter blocked
  all round, by a whole Seam Blocked modifier or by red painting, Random put
  the seam on the closing vertex of every layer and Aligned stopped aligning.
- The whole-perimeter Blocked warning flags only the highest whole zone, the
  one in effect. A lower whole zone it overwrites is no longer reported, and
  the candidate scan runs only when that zone is Blocked.
- The warning msgids take the type name from the menu's "Seam Blocked" msgid.
- PreciseSeamWarnings::set() shares the load-before-store idiom, and every
  weak segment records its modifier.
- Tests: a whole Blocked perimeter gets the seams of an unmarked one under
  every seam position; overwritten whole Blocked zones are not reported.

---------

Co-authored-by: Ian Bassi <ian.bassi@outlook.com>

src/libslic3r/GCode/PreciseSeam.cpp

@@ -673,7 +673,7 @@ static void refine_at_vertex(
     }
 }
 
-// Records one extraction for the warnings: the type of a modifier with a discarded fragment, and the
+// Records one extraction for the warnings: the type of a modifier with a discarded fragment, the
 // evaluated/reached flags for "had no effect" (a discarded fragment counts as reached, a contact not).
 static void record_extraction(PreciseSeamWarnings *warnings, const ModelVolume *modifier,
                               const SegmentExtraction &extracted)
@@ -685,13 +685,10 @@ static void record_extraction(PreciseSeamWarnings *warnings, const ModelVolume *
     const auto it = warnings->modifier_usage.find(modifier);
     if (it == warnings->modifier_usage.end())
         return;
-    // Load before store: most calls find the flag already set, so shared cache lines stay clean.
     PreciseSeamWarnings::ModifierUsage &usage = it->second;
-    if (!usage.checked.load(std::memory_order_relaxed))
-        usage.checked.store(true, std::memory_order_relaxed);
-    const bool reached = !extracted.segments.empty() || extracted.full_containment || extracted.discarded_fragments > 0;
-    if (reached && !usage.reached.load(std::memory_order_relaxed))
-        usage.reached.store(true, std::memory_order_relaxed);
+    PreciseSeamWarnings::set(usage.checked);
+    if (!extracted.segments.empty() || extracted.full_containment || extracted.discarded_fragments > 0)
+        PreciseSeamWarnings::set(usage.reached);
 }
 
 // Strong priority is per modifier, never a global maximum across different modifiers.
@@ -953,22 +950,15 @@ std::vector<WeakModifierSegment> collect_weak_modifier_segments(
         const SegmentExtraction extracted = extract_perimeter_segments(prepared, it->second[layer_id], modifier_volume->type(), context);
         record_extraction(warnings, modifier_volume, extracted);
         const auto type = convert_weak_modifier_type(modifier_volume->type());
-        // Full containment works like seam painting: Enforced and Neutral type the whole perimeter;
-        // Blocked is skipped with a warning, since the seam cannot avoid the whole perimeter.
+        // Full containment works like seam painting all round: the whole perimeter takes the type.
+        // A perimeter left whole Blocked also gets a warning (see apply_weak_modifiers_to_perimeter()).
         if (extracted.full_containment) {
-            if (type == EnforcedBlockedSeamPoint::Blocked) {
-                if (warnings)
-                    PreciseSeamWarnings::mark(warnings->full_containment, modifier_volume->type());
-                continue;
-            }
-            WeakModifierSegment whole{type, Point(), PerimeterPosition{0, 0.}, Point(), PerimeterPosition{0, 0.}};
-            whole.whole_perimeter = true;
-            result.push_back(whole);
+            result.push_back({type, Point(), PerimeterPosition{0, 0.}, Point(), PerimeterPosition{0, 0.}, true, modifier_volume});
             continue;
         }
         for (const PerimeterSegment &segment : extracted.segments) {
             result.push_back({type, segment.polyline.points.front(), segment.begin,
-                                   segment.polyline.points.back(), segment.end});
+                                   segment.polyline.points.back(), segment.end, false, modifier_volume});
         }
     }
     // Boundary insertion, refinement and last-write-wins priority use the established path.
@@ -979,7 +969,8 @@ void apply_weak_modifiers_to_perimeter(
     const std::vector<WeakModifierSegment> &weak_segments,
     PrintObjectSeamData::LayerSeams &result,
     const SeamPlacerImpl::Perimeter &perimeter,
-    bool &some_point_enforced)
+    bool &some_point_enforced,
+    PreciseSeamWarnings *warnings)
 {
     // Get z-coordinate for unscaling boundary points
     const float z_coord = result.points[perimeter.start_index].position.z();
@@ -1029,6 +1020,19 @@ void apply_weak_modifiers_to_perimeter(
             some_point_enforced = true;
         }
     }
+
+    // Only the highest whole zone is in effect, and a higher band may still unblock part of it.
+    if (warnings == nullptr)
+        return;
+    const auto last_whole = std::find_if(weak_segments.rbegin(), weak_segments.rend(),
+                                         [](const WeakModifierSegment &segment) { return segment.whole_perimeter; });
+    if (last_whole == weak_segments.rend() || last_whole->type != EnforcedBlockedSeamPoint::Blocked)
+        return;
+    for (size_t i = perimeter.start_index; i < perimeter.end_index; ++i)
+        if (result.points[i].type != EnforcedBlockedSeamPoint::Blocked)
+            return;
+    if (const auto usage = warnings->modifier_usage.find(last_whole->modifier); usage != warnings->modifier_usage.end())
+        PreciseSeamWarnings::set(usage->second.fully_blocked);
 }
 
 // Restore precise seam positions that may have been modified