Add entry with basic text editing and validation for numbers

include/gui/Entry.hpp

@@ -0,0 +1,36 @@
+#pragma once
+
+#include "Widget.hpp"
+#include <functional>
+
+#include <mglpp/graphics/Color.hpp>
+#include <mglpp/graphics/Text.hpp>
+
+namespace gsr {
+    using EntryValidateHandler = std::function<bool(std::string &str)>;
+
+    class Entry : public Widget {
+    public:
+        Entry(mgl::Font *font, const char *text, float max_width);
+        Entry(const Entry&) = delete;
+        Entry& operator=(const Entry&) = delete;
+
+        bool on_event(mgl::Event &event, mgl::Window &window, mgl::vec2f offset) override;
+        void draw(mgl::Window &window, mgl::vec2f offset) override;
+
+        mgl::vec2f get_size() override;
+
+        void set_string(std::string str);
+
+        // Return false to specify that the string should not be accepted. This reverts the string back to its previous value.
+        // The input can be changed by changing the input parameter and returning true.
+        EntryValidateHandler validate_handler;
+    private:
+        mgl::Text text;
+        float max_width;
+        bool selected = false;
+        float caret_offset_x = 0.0f;
+    };
+
+    EntryValidateHandler create_entry_validator_integer_in_range(int min, int max);
+}