Animate items emerging from building output ports

src/lib/sim/BeltSlot.cpp

@@ -0,0 +1,45 @@
+#include "BeltSlot.h"
+
+#include <cstddef>
+
+void advanceBeltSlots(std::vector<BeltItemSlot>& slots, double progressPerTick)
+{
+    for (std::size_t i = 0; i < slots.size(); ++i)
+    {
+        slots[i].progress += progressPerTick;
+
+        // Absolute cap: slot i cannot exceed 1.0 - i * 0.25.
+        const double absoluteCap = 1.0 - static_cast<double>(i) * 0.25;
+        if (slots[i].progress > absoluteCap)
+        {
+            slots[i].progress = absoluteCap;
+        }
+
+        // Gap constraint: must stay 0.25 behind the slot ahead.
+        if (i > 0)
+        {
+            const double gapCap = slots[i - 1].progress - 0.25;
+            if (slots[i].progress > gapCap)
+            {
+                slots[i].progress = (gapCap < 0.0 ? 0.0 : gapCap);
+            }
+        }
+    }
+}
+
+QPointF beltSlotWorldPos(QPoint tile, Rotation dir, double progress)
+{
+    // Map progress [0, 1] along the belt direction to a fractional tile-unit position.
+    // Progress 0 = entered from opposite side; 1 = at output edge.
+    const double baseX = tile.x() + 0.5;
+    const double baseY = tile.y() + 0.5;
+
+    switch (dir)
+    {
+        case Rotation::North: return {baseX, baseY - (progress - 0.5)};
+        case Rotation::East:  return {baseX + (progress - 0.5), baseY};
+        case Rotation::South: return {baseX, baseY + (progress - 0.5)};
+        case Rotation::West:  return {baseX - (progress - 0.5), baseY};
+    }
+    return {baseX, baseY};
+}