feat(ecs): introduce component view

Closes: #1
2026-09-07 23:05:39 +02:00
parent 320eb29957
commit 6639127bcf
4 changed files with 285 additions and 2 deletions
@@ -0,0 +1,124 @@
+#ifndef LIBCATBOY_ECS_COMPONENT_VIEW_HPP
+#define LIBCATBOY_ECS_COMPONENT_VIEW_HPP
+
+#include "sparseSet.hpp"
+
+#include <array>
+#include <concepts>
+#include <cstddef>
+#include <iterator>
+#include <tuple>
+#include <utility>
+
+namespace libcatboy {
+namespace ecs {
+
+template <std::integral Entity, typename... Sum>
+    requires(sizeof...(Sum) >= 1)
+class component_view {
+    friend class iterator;
+public:
+    class iterator {
+        friend class component_view;
+    private:
+        iterator(component_view* view, std::size_t index)
+          : m_view(view), m_denseMap(view->m_minimal->dense_map()), m_index(index) {
+            find_valid();
+        }
+    public:
+        using value_type        = std::tuple<Entity, Sum...>;
+        using difference_type   = std::ptrdiff_t;
+        using reference         = std::tuple<Entity, Sum&...>;
+        using iterator_category = std::forward_iterator_tag;
+    public:
+        reference operator*() { return std::tuple_cat(std::make_tuple(index()), current_tuple()); }
+
+        iterator& operator++() {
+            ++m_index;
+            find_valid();
+            return *this;
+        }
+
+        iterator operator++(int) {
+            iterator ret = *this;
+            ++(*this);
+            return ret;
+        }
+    public:
+        bool operator==(const iterator& rhs) const noexcept { return m_view == rhs.m_view && m_index == rhs.m_index; }
+
+        bool operator!=(const iterator& rhs) const noexcept { return m_view != rhs.m_view || m_index != rhs.m_index; }
+    public:
+        void swap(iterator& other) noexcept {
+            std::swap(m_view, other.m_view);
+            std::swap(m_denseMap, other.m_denseMap);
+            std::swap(m_index, other.m_index);
+        }
+    private:
+        void find_valid() {
+            while (m_index < m_denseMap.size() && !m_view->valid(index()))
+                ++m_index;
+        }
+    private:
+        using component_types = std::tuple<Sum...>;
+    private:
+        auto current_tuple() { return current_tuple(std::make_index_sequence<sizeof...(Sum)>{}); }
+
+        template <std::size_t... Is>
+        auto current_tuple(std::index_sequence<Is...>) {
+            return std::forward_as_tuple(
+                (reinterpret_cast<sparse_set<std::tuple_element_t<Is, component_types>>&>(*m_view->m_sets[Is])
+                        .at(index()))...);
+        }
+
+        auto current_tuple() const { return current_tuple(std::make_index_sequence<sizeof...(Sum)>{}); }
+
+        template <std::size_t... Is>
+        auto current_tuple(std::index_sequence<Is...>) const {
+            return std::forward_as_tuple(
+                (reinterpret_cast<const sparse_set<std::tuple_element_t<Is, component_types>>&>(*m_view->m_sets[Is])
+                        .at(index()))...);
+        }
+    private:
+        std::size_t index() const noexcept { return m_denseMap[m_index]; }
+    private:
+        component_view*        m_view;
+        std::span<std::size_t> m_denseMap;
+        std::size_t            m_index = 0;
+    };
+public:
+    component_view(std::array<isparse_set*, sizeof...(Sum)> sets)
+      : m_sets(sets), m_minimal(sets.front()) {
+        for (std::size_t i = 1; i < sets.size(); ++i) {
+            if (m_minimal->size() > sets[i]->size())
+                m_minimal = sets[i];
+        }
+    }
+public:
+    std::size_t size() const noexcept {
+        std::size_t count = 0;
+        for (auto idx : m_minimal->dense_map()) {
+            if (valid(idx)) ++count;
+        }
+        return count;
+    }
+public:
+    iterator begin() { return { this, 0 }; }
+    iterator end() { return { this, m_minimal->size() }; }
+private:
+    bool valid(Entity entity) const noexcept {
+        for (isparse_set* set : m_sets) {
+            if (!set->contains(entity)) return false;
+        }
+        return true;
+    }
+private:
+    std::array<isparse_set*, sizeof...(Sum)> m_sets;
+
+    isparse_set* m_minimal = nullptr;
+};
+
+} // namespace ecs
+} // namespace libcatboy
+
+#endif // LIBCATBOY_ECS_COMPONENT_VIEW_HPP