Input w bibliotece SDL2

Question

Obecnie staram się zrobić input w bibliotece SDL2. Brakuje już tylko jednej rzeczy, kiedy jest za dużo tekstu i użytkownik ma kursor na lewej krawędzi, oraz klika strzałkę w lewo, tekst powinien przesuwać się w prawo. Ma ktoś pomysł, jak to zrobić? Obecny kod:

struct Input {
	SDL_Rect r{};
	Text text;
	SDL_Rect cursorR{};
	int currentLetter = 0; // NOTE: 0 == cursor is before first letter or on r.x on empty string

	void handleEvent(SDL_Event event, SDL_Renderer* renderer, TTF_Font* font)
		{
		if (event.type == SDL_KEYDOWN) {
			if (event.key.keysym.scancode == SDL_SCANCODE_BACKSPACE) {
				if (currentLetter) {
					utf8Erase(text.text, currentLetter - 1);
					text.setText(renderer, font, text.text, {});
					--currentLetter;
					cursorR.x = calcCursorX(currentLetter, text, renderer, font, r);
				}
			}
			else if (event.key.keysym.scancode == SDL_SCANCODE_LEFT) {
				if (currentLetter) {
					--currentLetter;
					cursorR.x = calcCursorX(currentLetter, text, renderer, font, r);
				}
			}
			else if (event.key.keysym.scancode == SDL_SCANCODE_RIGHT) {
				if (currentLetter != utf8ToUcs4(text.text).size()) {
					++currentLetter;
					cursorR.x = calcCursorX(currentLetter, text, renderer, font, r);
				}
			}
		}
		else if (event.type == SDL_TEXTINPUT) {
			utf8Insert(text.text, currentLetter, event.text.text);
			text.setText(renderer, font, text.text, {});
			++currentLetter;
			cursorR.x = calcCursorX(currentLetter, text, renderer, font, r);
		}
	}

	void draw(SDL_Renderer* renderer, TTF_Font* font)
	{
		SDL_SetRenderDrawColor(renderer, 255, 255, 255, 0);
		SDL_RenderFillRect(renderer, &r);
		static Text t;
		t = text;
		int count = 0;
		while (t.dstR.x + t.dstR.w > r.x + r.w) {
			utf8Erase(t.text, 0);
			t.setText(renderer, font, t.text, {});
			--currentLetter;
			cursorR.x = calcCursorX(currentLetter, text, renderer, font, r);
			++count;
		}
		t.draw(renderer);
		SDL_SetRenderDrawColor(renderer, 0, 255, 0, 0);
		SDL_RenderFillRect(renderer, &cursorR);
		for (int i = 0; i < count; ++i) {
			++currentLetter;
			cursorR.x = calcCursorX(currentLetter, text, renderer, font, r);
		}
	}
};

Tutaj kod struktury Text oraz funkcja renderText:

SDL_Texture* renderText(SDL_Texture* previousTexture, TTF_Font* font, SDL_Renderer* renderer, const std::string& text, SDL_Color color)
{
	if (previousTexture) {
		SDL_DestroyTexture(previousTexture);
	}
	SDL_Surface* surface;
	if (text.empty()) {
		surface = TTF_RenderUTF8_Blended(font, " ", color);
	}
	else {
		surface = TTF_RenderUTF8_Blended(font, text.c_str(), color);
	}
	if (surface) {
		SDL_Texture* texture = SDL_CreateTextureFromSurface(renderer, surface);
		SDL_FreeSurface(surface);
		return texture;
	}
	else {
		return 0;
	}
}

struct Text {
	std::string text;
	SDL_Surface* surface = 0;
	SDL_Texture* t = 0;
	SDL_FRect dstR{};
	bool autoAdjustW = false;
	bool autoAdjustH = false;
	float wMultiplier = 1;
	float hMultiplier = 1;

	~Text()
	{
		if (surface) {
			SDL_FreeSurface(surface);
		}
		if (t) {
			SDL_DestroyTexture(t);
		}
	}

	Text()
	{

	}

	Text(const Text& rightText)
	{
		text = rightText.text;
		if (surface) {
			SDL_FreeSurface(surface);
		}
		if (t) {
			SDL_DestroyTexture(t);
		}
		if (rightText.surface) {
			surface = SDL_ConvertSurface(rightText.surface, rightText.surface->format, SDL_SWSURFACE);
		}
		if (rightText.t) {
			t = SDL_CreateTextureFromSurface(renderer, surface);
		}
		dstR = rightText.dstR;
		autoAdjustW = rightText.autoAdjustW;
		autoAdjustH = rightText.autoAdjustH;
		wMultiplier = rightText.wMultiplier;
		hMultiplier = rightText.hMultiplier;
	}

	Text& operator=(const Text& rightText)
	{
		text = rightText.text;
		if (surface) {
			SDL_FreeSurface(surface);
		}
		if (t) {
			SDL_DestroyTexture(t);
		}
		if (rightText.surface) {
			surface = SDL_ConvertSurface(rightText.surface, rightText.surface->format, SDL_SWSURFACE);
		}
		if (rightText.t) {
			t = SDL_CreateTextureFromSurface(renderer, surface);
		}
		dstR = rightText.dstR;
		autoAdjustW = rightText.autoAdjustW;
		autoAdjustH = rightText.autoAdjustH;
		wMultiplier = rightText.wMultiplier;
		hMultiplier = rightText.hMultiplier;
		return *this;
	}

	void setText(SDL_Renderer* renderer, TTF_Font* font, std::string text, SDL_Color c = { 255,255,255 })
	{
		this->text = text;
#if 1 // NOTE: renderText
		if (surface) {
			SDL_FreeSurface(surface);
		}
		if (t) {
			SDL_DestroyTexture(t);
		}
		if (text.empty()) {
			surface = TTF_RenderUTF8_Blended(font, " ", c);
		}
		else {
			surface = TTF_RenderUTF8_Blended(font, text.c_str(), c);
		}
		if (surface) {
			t = SDL_CreateTextureFromSurface(renderer, surface);
		}
#endif
		if (autoAdjustW) {
			SDL_QueryTextureF(t, 0, 0, &dstR.w, 0);
		}
		if (autoAdjustH) {
			SDL_QueryTextureF(t, 0, 0, 0, &dstR.h);
		}
		dstR.w *= wMultiplier;
		dstR.h *= hMultiplier;
	}

	void setText(SDL_Renderer* renderer, TTF_Font* font, int value, SDL_Color c = { 255,255,255 })
	{
		setText(renderer, font, std::to_string(value), c);
	}

	void draw(SDL_Renderer* renderer)
	{
		if (t) {
			SDL_RenderCopyF(renderer, t, 0, &dstR);
		}
	}
};