Properly link flecs library

engine/libs/flecs/examples/cpp/queries/group_by/include/group_by.h

@@ -0,0 +1,16 @@
+#ifndef GROUP_BY_H
+#define GROUP_BY_H
+
+/* This generated file contains includes for project dependencies */
+#include "group_by/bake_config.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+

engine/libs/flecs/examples/cpp/queries/group_by/include/group_by/bake_config.h

@@ -0,0 +1,24 @@
+/*
+                                   )
+                                  (.)
+                                  .|.
+                                  | |
+                              _.--| |--._
+                           .-';  ;`-'& ; `&.
+                          \   &  ;    &   &_/
+                           |"""---...---"""|
+                           \ | | | | | | | /
+                            `---.|.|.|.---'
+
+ * This file is generated by bake.lang.c for your convenience. Headers of
+ * dependencies will automatically show up in this file. Include bake_config.h
+ * in your main project file. Do not edit! */
+
+#ifndef GROUP_BY_BAKE_CONFIG_H
+#define GROUP_BY_BAKE_CONFIG_H
+
+/* Headers of public dependencies */
+#include <flecs.h>
+
+#endif
+

engine/libs/flecs/examples/cpp/queries/group_by/project.json

@@ -0,0 +1,11 @@
+{
+    "id": "group_by",
+    "type": "application",
+    "value": {
+        "use": [
+            "flecs"
+        ],
+        "language": "c++",
+        "public": false
+    }
+}

engine/libs/flecs/examples/cpp/queries/group_by/src/main.cpp

@@ -0,0 +1,113 @@
+#include <group_by.h>
+#include <iostream>
+
+// Group by is a feature of cached queries that allows applications to assign a
+// group id to each matched table. Tables that are assigned the same group id
+// are stored together in "groups". This ensures that when a query is iterated,
+// tables that share a group are iterated together.
+//
+// Groups in the cache are ordered by group id, which ensures that tables with
+// lower ids are iterated before table with higher ids. This is the same 
+// mechanism that is used by the cascade feature, which groups tables by depth
+// in a relationship hierarchy.
+//
+// This makes groups a more efficient, though less granular mechanism for 
+// ordering entities. Order is maintained at the group level, which means that
+// once a group is created, tables can get added and removed to the group
+// with is an O(1) operation.
+//
+// Groups can also be used as an efficient filtering mechanism. See the 
+// set_group example for more details.
+
+struct Position {
+    double x, y;
+};
+
+// Dummy tag to put entities in different tables
+struct Tag { };
+
+// Create a relationship to use for the group_by function. Tables will
+// be assigned the relationship target as group id
+struct Group { };
+
+// Targets for the relationship, which will be used as group ids.
+struct First { };
+struct Second { };
+struct Third { };
+
+int main() {
+    flecs::world ecs;
+
+    // Register components in order so that id for First is lower than Third
+    ecs.component<First>();
+    ecs.component<Second>();
+    ecs.component<Third>();
+
+    // Grouped query
+    flecs::query<Position> q = ecs.query_builder<Position>()
+        .group_by<Group>()
+        .build();
+
+    // Create entities in 6 different tables with 3 group ids
+    ecs.entity().add<Group, Third>()
+        .set<Position>({1, 1});
+    ecs.entity().add<Group, Second>()
+        .set<Position>({2, 2});
+    ecs.entity().add<Group, First>()
+        .set<Position>({3, 3});
+
+    ecs.entity().add<Group, Third>()
+        .set<Position>({4, 4})
+        .add<Tag>();
+    ecs.entity().add<Group, Second>()
+        .set<Position>({5, 5})
+        .add<Tag>();
+    ecs.entity().add<Group, First>()
+        .set<Position>({6, 6})
+        .add<Tag>();
+
+    // The query cache now looks like this:
+    //  - group First:
+    //     - table [Position, (Group, First)]
+    //     - table [Postion, Tag, (Group, First)]
+    //
+    //  - group Second:
+    //     - table [Position, (Group, Second)]
+    //     - table [Postion, Tag, (Group, Second)]
+    //  
+    //  - group Third:
+    //     - table [Position, (Group, Third)]
+    //     - table [Postion, Tag, (Group, Third)]
+    //
+
+    q.iter([&](flecs::iter& it, Position *p) {
+        flecs::entity group = ecs.entity(it.group_id());
+        std::cout << " - group " << group.path() << ": table ["
+            << it.table().str() << "]\n";
+
+        for (auto i : it) {
+            std::cout << "     {" << p[i].x << ", " << p[i].y << "}\n";
+        }
+
+        std::cout << "\n";
+    });
+
+    // Output:
+    //  - group ::First: table [Position, (Group,First)]
+    //      {3, 3}
+    // 
+    //  - group ::First: table [Position, Tag, (Group,First)]
+    //      {6, 6}
+    // 
+    //  - group ::Second: table [Position, (Group,Second)]
+    //      {2, 2}
+    // 
+    //  - group ::Second: table [Position, Tag, (Group,Second)]
+    //      {5, 5}
+    // 
+    //  - group ::Third: table [Position, (Group,Third)]
+    //      {1, 1}
+    // 
+    //  - group ::Third: table [Position, Tag, (Group,Third)]
+    //      {4, 4}
+}