Add brush and grid snapping functionality

src/core/selection.ts

@@ -3,3 +3,28 @@ export type EditorSelection =
   | { kind: "brushes"; ids: string[] }
   | { kind: "entities"; ids: string[] }
   | { kind: "modelInstances"; ids: string[] };
+
+export function cloneEditorSelection(selection: EditorSelection): EditorSelection {
+  if (selection.kind === "none") {
+    return {
+      kind: "none"
+    };
+  }
+
+  return {
+    kind: selection.kind,
+    ids: [...selection.ids]
+  };
+}
+
+export function getSingleSelectedBrushId(selection: EditorSelection): string | null {
+  if (selection.kind !== "brushes" || selection.ids.length !== 1) {
+    return null;
+  }
+
+  return selection.ids[0];
+}
+
+export function isBrushSelected(selection: EditorSelection, brushId: string): boolean {
+  return selection.kind === "brushes" && selection.ids.includes(brushId);
+}