Lazy line caching for Notepad (#1042)

* easier 'now', start adding text editor

* Adding scrolling to notepad

* Better scrolling

* Better scrolling, off-by-1 bugs

* MVP fit and finish

* Add tiny font and use in Notepad

* Font tweaking, tiny font cursor

* Fix warning

* Format changed files

* WIP No file limit

* WIP - adding CircularBuffer type

* WIP Caching

* add  unit test for circular_buffer

* WIP still have a bug when moving cache forward

* Finish lazy line caching

---------

Co-authored-by: kallanreed <kallanreed@outlook.com>

firmware/common/circular_buffer.hpp

@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2023 Kyle Reed
+ *
+ * This file is part of PortaPack.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __CIRCULAR_BUFFER_H__
+#define __CIRCULAR_BUFFER_H__
+
+#include <stddef.h>  // For size_t
+#include <memory>
+
+/* Implements a fixed-size, circular buffer.
+ * NB: Holds Capacity - 1 items.
+ * There are no bounds checks on accessors so ensure there are
+ * items in the buffer before accessing front/back/operator[]. */
+template <typename T, size_t Capacity>
+class CircularBuffer {
+   public:
+    CircularBuffer() = default;
+
+    CircularBuffer(const CircularBuffer&) = delete;
+    CircularBuffer(CircularBuffer&&) = delete;
+    CircularBuffer& operator=(const CircularBuffer&) = delete;
+    CircularBuffer& operator=(CircularBuffer&&) = delete;
+
+    void push_front(T val) {
+        head_ = head_ > 0 ? head_ - 1 : last_index;
+        if (head_ == end_)
+            pop_back_internal();
+
+        data_[head_] = std::move(val);
+    }
+
+    void pop_front() {
+        if (!empty())
+            pop_front_internal();
+    }
+
+    void push_back(T val) {
+        data_[end_] = std::move(val);
+
+        end_ = end_ < last_index ? end_ + 1 : 0;
+        if (head_ == end_)
+            pop_front_internal();
+    }
+
+    void pop_back() {
+        if (!empty())
+            pop_back_internal();
+    }
+
+    T& operator[](size_t ix) & {
+        ix += head_;
+        if (ix >= Capacity)
+            ix -= Capacity;
+        return data_[ix];
+    }
+
+    const T& operator[](size_t ix) const& {
+        return const_cast<CircularBuffer*>(this)->operator[](ix);
+    }
+
+    const T& front() const& {
+        return data_[head_];
+    }
+
+    const T& back() const& {
+        auto end = end_ > 0 ? end_ - 1 : last_index;
+        return data_[end];
+    }
+
+    size_t size() const& {
+        auto end = end_;
+        if (end < head_)
+            end += Capacity;
+        return end - head_;
+    }
+
+    bool empty() const {
+        return head_ == end_;
+    }
+
+    void clear() {
+        head_ = 0;
+        end_ = 0;
+    }
+
+   private:
+    void pop_front_internal() {
+        head_ = head_ < last_index ? head_ + 1 : 0;
+    }
+
+    void pop_back_internal() {
+        end_ = end_ > 0 ? end_ - 1 : last_index;
+    }
+
+    static constexpr size_t last_index = Capacity - 1;
+    size_t head_{0};
+    size_t end_{0};
+
+    T data_[Capacity]{};
+};
+
+#endif /*__CIRCULAR_BUFFER_H__*/