1 files changed, 97 insertions, 0 deletions
diff --git a/engine/structures/Grid.ts b/engine/structures/Grid.ts
new file mode 100644
index 0000000..d359909
--- /dev/null
+++ b/engine/structures/Grid.ts
@@ -0,0 +1,97 @@
+import type { Coord2D, Dimension2D } from "../interfaces";
+import type { RefreshingCollisionFinderBehavior } from ".";
+
+export class Grid implements RefreshingCollisionFinderBehavior {
+  private cellEntities: Map<number, string[]>;
+
+  private gridDimension: Dimension2D;
+  private cellDimension: Dimension2D;
+  private topLeft: Coord2D;
+
+  constructor(
+    gridDimension: Dimension2D,
+    cellDimension: Dimension2D,
+    topLeft = { x: 0, y: 0 },
+  ) {
+    this.gridDimension = gridDimension;
+    this.cellDimension = cellDimension;
+    this.topLeft = topLeft;
+
+    this.cellEntities = new Map();
+  }
+
+  public insert(boxedEntry: BoxedEntry) {
+    this.getOverlappingCells(boxedEntry).forEach((gridIdx) => {
+      if (!this.cellEntities.has(gridIdx)) {
+        this.cellEntities.set(gridIdx, []);
+      }
+      this.cellEntities.get(gridIdx).push(boxedEntry.id);
+    });
+  }
+
+  public getNeighborIds(boxedEntry: BoxedEntry): Set<string> {
+    const neighborIds: Set<string> = new Set();
+    this.getOverlappingCells(boxedEntry).forEach((gridIdx) => {
+      if (this.cellEntities.has(gridIdx)) {
+        this.cellEntities.get(gridIdx).forEach((id) => neighborIds.add(id));
+      }
+    });
+    return neighborIds;
+  }
+
+  public clear() {
+    this.cellEntities.clear();
+  }
+
+  public setTopLeft(topLeft: Coord2D) {
+    this.topLeft = topLeft;
+  }
+
+  public setDimension(dimension: Dimension2D) {
+    this.gridDimension = dimension;
+  }
+
+  public setCellDimension(cellDimension: Dimension2D) {
+    this.cellDimension = cellDimension;
+  }
+
+  private getOverlappingCells(boxedEntry: BoxedEntry): number[] {
+    const { center, dimension } = boxedEntry;
+    const yBoxes = Math.ceil(
+      this.gridDimension.height / this.cellDimension.height,
+    );
+    const xBoxes = Math.ceil(
+      this.gridDimension.width / this.cellDimension.width,
+    );
+
+    const translated: Coord2D = {
+      y: center.y - this.topLeft.y,
+      x: center.x - this.topLeft.x,
+    };
+
+    const topLeftBox = {
+      x: Math.floor(
+        (translated.x - dimension.width / 2) / this.cellDimension.width,
+      ),
+      y: Math.floor(
+        (translated.y - dimension.height / 2) / this.cellDimension.height,
+      ),
+    };
+    const bottomRightBox = {
+      x: Math.floor(
+        (translated.x + dimension.width / 2) / this.cellDimension.width,
+      ),
+      y: Math.floor(
+        (translated.y + dimension.height / 2) / this.cellDimension.height,
+      ),
+    };
+
+    const cells: number[] = [];
+
+    for (let y = topLeftBox.y; y <= bottomRightBox.y; ++y)
+      for (let x = topLeftBox.x; x <= bottomRightBox.x; ++x)
+        cells.push(yBoxes * y + x);
+
+    return cells;
+  }
+}