Reveal port items in a thin margin at machine edges

src/ui/GameWorldView.cpp

@@ -20,6 +20,7 @@
 #include <QPainter>
 #include <QPen>
 #include <QPolygonF>
+#include <QRegion>
 #include <QStringList>
 #include <QTimer>
 
@@ -402,12 +403,12 @@ void GameWorldView::paintGL()
     painter.setRenderHint(QPainter::Antialiasing, false);
 
     drawTiles(painter);
-    // Port items are drawn before the buildings so the building body occludes the
-    // portion still inside the footprint: items appear to slide out of the output
-    // port (REQ-MAT-OUTPUT-EMERGE) and into the input port (REQ-MAT-INPUT-INTAKE)
-    // rather than popping in or out of existence.
-    drawPortItems(painter);
     drawBuildings(painter);
+    // Port items are drawn over the buildings but clipped to a thin margin at each
+    // machine's edges (see drawPortItems), so items appear to emerge from / sink
+    // into the port and stay visible while crossing directly between two touching
+    // buildings (REQ-MAT-OUTPUT-EMERGE, REQ-MAT-INPUT-INTAKE, REQ-MAT-DIRECT-COUPLE).
+    drawPortItems(painter);
     drawCopyConfigFeedback(painter);
     drawStations(painter);
     drawBeltItems(painter);
@@ -1162,9 +1163,39 @@ void GameWorldView::drawPortItems(QPainter& painter)
 {
     const float halfPx = tilePx() * 0.5f * 0.5f;
 
-    // Shared with belt items (REQ-GW-TILE-SIZE): a half-tile filled square with an
-    // outline, occluded by the building drawn afterwards so the item slides out of
-    // (REQ-MAT-OUTPUT-EMERGE) or into (REQ-MAT-INPUT-INTAKE) the port.
+    // Port items are drawn over the buildings (drawBuildings runs first) but clipped
+    // to a thin margin at each machine's edges: the clip region is the whole view
+    // minus every machine's interior (its footprint inset by kPortMarginTiles). So a
+    // transiting item shows only near the port edge — appearing to emerge from / sink
+    // into the machine (REQ-MAT-OUTPUT-EMERGE, REQ-MAT-INPUT-INTAKE) and staying
+    // visible in the ~2×margin band at a seam between two touching buildings
+    // (REQ-MAT-DIRECT-COUPLE). Transport tiles are not machines and never occlude, so
+    // items on belts stay fully visible.
+    constexpr double kPortMarginTiles = 0.2;
+    const double margin = kPortMarginTiles * static_cast<double>(tilePx());
+
+    QRegion clip(rect());
+    for (const Building& b : m_sim->buildings().allBuildings())
+    {
+        if (b.type == BuildingType::Belt || b.type == BuildingType::Splitter
+            || b.type == BuildingType::TunnelEntry || b.type == BuildingType::TunnelExit)
+        {
+            continue;
+        }
+        const std::set<QPoint, QPointCompare> cells(b.bodyCells.begin(), b.bodyCells.end());
+        for (const QPoint& cell : b.bodyCells)
+        {
+            // Inset an edge only where the neighbouring cell is not part of the same
+            // building, so interior cell seams stay filled (handles L-shaped footprints).
+            const double l = cells.count(cell + QPoint(-1,  0)) ? 0.0 : margin;
+            const double t = cells.count(cell + QPoint( 0, -1)) ? 0.0 : margin;
+            const double r = cells.count(cell + QPoint( 1,  0)) ? 0.0 : margin;
+            const double d = cells.count(cell + QPoint( 0,  1)) ? 0.0 : margin;
+            clip = clip.subtracted(QRegion(tileRect(cell).adjusted(l, t, -r, -d).toRect()));
+        }
+    }
+
+    // Shared with belt items (REQ-GW-TILE-SIZE): a half-tile filled square + outline.
     const std::function<void(const ItemType&, QPointF)> drawItem =
         [&](const ItemType& type, QPointF worldPos)
     {
@@ -1175,16 +1206,19 @@ void GameWorldView::drawPortItems(QPainter& painter)
         const QPointF center = worldToWidget(
             QVector2D(static_cast<float>(worldPos.x()),
                       static_cast<float>(worldPos.y())));
-        const QRectF rect(center.x() - halfPx, center.y() - halfPx,
-                          halfPx * 2, halfPx * 2);
-        painter.fillRect(rect, it->second.fill);
+        const QRectF itemRect(center.x() - halfPx, center.y() - halfPx,
+                              halfPx * 2, halfPx * 2);
+        painter.fillRect(itemRect, it->second.fill);
         painter.setPen(QPen(it->second.outline, 1));
         painter.setBrush(Qt::NoBrush);
-        painter.drawRect(rect);
+        painter.drawRect(itemRect);
     };
 
+    painter.save();
+    painter.setClipRegion(clip);
     m_sim->buildings().forEachEmergingItem(drawItem);
     m_sim->buildings().forEachIncomingItem(drawItem);
+    painter.restore();
 }
 
 void GameWorldView::drawBeltItems(QPainter& painter)