Working template (RmlUi 6.2)

Needs:
- Lua plugin
- SVG plugin

vendor/rmlui_backend/RmlUi_Platform_SDL.h

@@ -0,0 +1,62 @@
+#pragma once
+
+#include <RmlUi/Core/Input.h>
+#include <RmlUi/Core/SystemInterface.h>
+#include <RmlUi/Core/Types.h>
+
+#if RMLUI_SDL_VERSION_MAJOR == 3
+	#include <SDL3/SDL.h>
+#elif RMLUI_SDL_VERSION_MAJOR == 2
+	#include <SDL.h>
+#else
+	#error "Unspecified RMLUI_SDL_VERSION_MAJOR. Please set this definition to the major version of the SDL library being linked to."
+#endif
+
+class SystemInterface_SDL : public Rml::SystemInterface {
+public:
+	SystemInterface_SDL();
+	~SystemInterface_SDL();
+
+	// Optionally, provide or change the window to be used for setting the mouse cursors.
+	void SetWindow(SDL_Window* window);
+
+	// -- Inherited from Rml::SystemInterface  --
+
+	double GetElapsedTime() override;
+
+	void SetMouseCursor(const Rml::String& cursor_name) override;
+
+	void SetClipboardText(const Rml::String& text) override;
+	void GetClipboardText(Rml::String& text) override;
+
+	void ActivateKeyboard(Rml::Vector2f caret_position, float line_height) override;
+	void DeactivateKeyboard() override;
+
+private:
+	SDL_Window* window = nullptr;
+
+	SDL_Cursor* cursor_default = nullptr;
+	SDL_Cursor* cursor_move = nullptr;
+	SDL_Cursor* cursor_pointer = nullptr;
+	SDL_Cursor* cursor_resize = nullptr;
+	SDL_Cursor* cursor_cross = nullptr;
+	SDL_Cursor* cursor_text = nullptr;
+	SDL_Cursor* cursor_unavailable = nullptr;
+};
+
+namespace RmlSDL {
+
+// Applies input on the context based on the given SDL event.
+// @return True if the event is still propagating, false if it was handled by the context.
+bool InputEventHandler(Rml::Context* context, SDL_Window* window, SDL_Event& ev);
+
+// Converts the SDL key to RmlUi key.
+Rml::Input::KeyIdentifier ConvertKey(int sdl_key);
+
+// Converts the SDL mouse button to RmlUi mouse button.
+int ConvertMouseButton(int sdl_mouse_button);
+
+// Returns the active RmlUi key modifier state.
+int GetKeyModifierState();
+
+} // namespace RmlSDL