preliminary work on ecs

src/ecs/sparse.zig

@@ -0,0 +1,36 @@
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+
+pub fn SparseSet(comptime T: type) type {
+    return struct {
+        sparse: std.ArrayList(usize),
+        dense: std.ArrayList(usize),
+        components: std.ArrayList(T),
+
+        pub fn init(allocator: Allocator) @This() {
+            return @This(){
+                .sparse = std.ArrayList(usize).init(allocator),
+                .dense = std.ArrayList(usize).init(allocator),
+                .components = std.ArrayList(T).init(allocator),
+            };
+        }
+
+        pub fn addEntity(self: *@This(), entity: usize, component: T) !void {
+            if (entity >= self.sparse.items.len) {
+                try self.sparse.resize(entity + 10);
+            }
+
+            self.sparse.items[entity] = self.dense.items.len;
+            try self.dense.append(entity);
+            try self.components.append(component);
+        }
+
+        pub fn removeEntity(self: *@This(), entity: usize) void {
+            const last_index = self.dense.getLast();
+            const dense_index = self.sparse.items[entity];
+            self.dense.swapRemove(dense_index);
+            self.components.swapRemove(dense_index);
+            self.sparse.items[last_index] = dense_index;
+        }
+    };
+}