feat(core): add chunk load/unload radius streaming

core/src/Streaming.cpp

@@ -0,0 +1,51 @@
+#include "vf/Streaming.h"
+
+#include <algorithm>
+
+namespace vf {
+
+namespace {
+
+long long distanceSquared(ColumnCoord a, ColumnCoord b) {
+    long long dx = a.x - b.x;
+    long long dz = a.z - b.z;
+    return dx * dx + dz * dz;
+}
+
+} // namespace
+
+std::vector<ColumnCoord> columnsInRadius(ColumnCoord centre, int radius) {
+    std::vector<ColumnCoord> columns;
+    long long limit = static_cast<long long>(radius) * radius;
+    for (int dz = -radius; dz <= radius; ++dz) {
+        for (int dx = -radius; dx <= radius; ++dx) {
+            ColumnCoord column{centre.x + dx, centre.z + dz};
+            if (distanceSquared(column, centre) <= limit) columns.push_back(column);
+        }
+    }
+    std::stable_sort(columns.begin(), columns.end(),
+                     [&](ColumnCoord lhs, ColumnCoord rhs) {
+                         return distanceSquared(lhs, centre) < distanceSquared(rhs, centre);
+                     });
+    return columns;
+}
+
+StreamDelta ChunkStreamer::update(ColumnCoord centre) {
+    StreamDelta delta;
+
+    for (ColumnCoord column : columnsInRadius(centre, config.loadRadius)) {
+        if (resident.count(column) == 0) delta.load.push_back(column);
+    }
+
+    long long unloadLimit = static_cast<long long>(config.unloadRadius) * config.unloadRadius;
+    for (ColumnCoord column : resident) {
+        if (distanceSquared(column, centre) > unloadLimit) delta.unload.push_back(column);
+    }
+
+    for (ColumnCoord column : delta.load) resident.insert(column);
+    for (ColumnCoord column : delta.unload) resident.erase(column);
+
+    return delta;
+}
+
+} // namespace vf