[Feat] (MG_State/GLState): Implement BufferObject.

MobileGL/MG_Util/Miscellany/IndexGenerator.h

@@ -0,0 +1,52 @@
+#pragma once
+
+namespace MobileGL {
+    template <typename IndexType>
+    class IndexGenerator {
+    public:
+        IndexGenerator() : next_index_(1) {}
+        explicit IndexGenerator(IndexType n) : next_index_(1) {
+            is_valid_.reserve(n);
+        }
+
+        void Generate(size_t n, IndexType* indices) {
+            if (n <= 0) {
+                return;
+            }
+
+            size_t count_from_freed = std::min(n, freed_indices_.size());
+            for (size_t i = 0; i < count_from_freed; ++i) {
+                indices[i] = freed_indices_.back();
+                freed_indices_.pop_back();
+                if (indices[i] >= is_valid_.size()) {
+                    is_valid_.resize(static_cast<size_t>(indices[i]) + 1, false);
+                }
+                is_valid_[indices[i]] = true;
+            }
+
+            for (size_t i = count_from_freed; i < n; ++i) {
+                indices[i] = next_index_++;
+                if (indices[i] >= is_valid_.size()) {
+                    is_valid_.resize(static_cast<size_t>(indices[i]) + 1, false);
+                }
+                is_valid_[indices[i]] = true;
+            }
+        }
+
+        void Delete(IndexType index) {
+            if (index < is_valid_.size() && is_valid_[index] == true) {
+                is_valid_[index] = false;
+                freed_indices_.push_back(index);
+            }
+        }
+
+        bool IsValid(IndexType index) const {
+            return index < is_valid_.size() && is_valid_[index] == true;
+        }
+
+    private:
+        IndexType next_index_;
+        std::vector<IndexType> freed_indices_;
+        std::vector<bool> is_valid_;
+    };
+}