radiantwave/src/scroller_page.cpp

#include "scroller_page.h"

#include "app_state.h"
#include "audio/audio_downloader.h"
#include "logical_size.h"
#include "proclamation_options_page.h"
#include "scramble/fibonacci_scrambler.h"
#include "timezone_helper.h"
#include "utf8_utils.h"

#include <SDL3/SDL.h>
#include <SDL3_ttf/SDL_ttf.h>
#include <algorithm>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <filesystem>
#include <vector>

using radiantwave::FibonacciLinePattern;
using radiantwave::scroller::ProclamationStream;

namespace {

constexpr float kFadeSeconds = 5.0f;
constexpr float kVelocityMin = -3500.0f;
constexpr float kVelocityMax = 3500.0f;

} // anonymous namespace

void ScrollerPage::onPush(AppState &state) {
	state_ = &state;

	// Save the current logical presentation (LETTERBOX at design resolution)
	// and switch to NONE so we render into the full physical window.  This
	// lets the scroller scroll the entire vertical extent of tall/rotated
	// displays while keeping text at the same pixel scale.  onPop restores
	// the original presentation for other pages.
	SDL_GetRenderLogicalPresentation(state.renderer, &savedLogicalW_,
									 &savedLogicalH_, &savedMode_);

	// Use the renderer's actual output size in pixels, not the window size in
	// points. SDL_GetWindowSize() returns screen coordinates, which can be
	// smaller than the real drawable if the display has a content scale
	// applied (common on some monitors/compositors) — that mismatch caused
	// this page to lay out and center within a sub-region of the screen
	// instead of the full physical canvas. SDL_GetRenderOutputSize() gives us
	// the true pixel dimensions of whatever we're actually rendering into.
	int windowW = 0;
	int windowH = 0;
	SDL_GetRenderOutputSize(state.renderer, &windowW, &windowH);
	if (windowW <= 0) {
		windowW = radiantwave::kDesignWidth;
	}
	if (windowH <= 0) {
		windowH = radiantwave::kDesignHeight;
	}

	SDL_SetRenderLogicalPresentation(state.renderer, windowW, windowH,
									 SDL_LOGICAL_PRESENTATION_DISABLED);

	screenW_ = static_cast<float>(windowW);
	screenH_ = static_cast<float>(windowH);
	// Lines are capped at the full screen width; the widest Fibonacci lines
	// are sized to fill it with whole words (peak word count derived from the
	// screen), independent of resolution.
	maxLineWidth_ = screenW_;

	TTF_Init();
	buildStreams(state);
	createFont(state);
	createPatterns();

	lines_.clear();
	prefilling_ = true;
	prefillLines();
	prefilling_ = false;

	// Start audio. In dynamic mode the current stream's solfeggio-frequency
	// track wins (when its file exists); otherwise the configured manual track
	// plays. A frequency file that is not on disk yet falls back to the manual
	// track rather than playing nothing. A schedule block with dynamicAudio=true
	// forces dynamic audio for its duration; false leaves the device setting be.
	std::string track = state.config.get().audio.current_track;
	if (effectiveDynamicAudio() && !streams_.empty()) {
		const ProclamationStream &stream = streams_[streamIndex_];
		if (stream.solfeggio_frequency_id != 0 &&
			!stream.audioFilename.empty() &&
			std::filesystem::exists(audioFilePath(stream.audioFilename))) {
			track = stream.audioFilename;
		}
	}
	if (std::filesystem::exists(audioFilePath(track))) {
		state.audio.playTrackFadeIn(track, kFadeSeconds);
	}

	state.keybinds.bind(SDLK_ESCAPE, "scroller_exit", [this]() {
		if (state_) {
			state_->pages.pop(*state_);
		}
	});
}

void ScrollerPage::onResume(AppState &state) {
	state_ = &state;
	createFont(state);
	createPatterns();
	rebuildWordTextures();

	state.keybinds.bind(SDLK_ESCAPE, "scroller_exit", [this]() {
		if (state_) {
			state_->pages.pop(*state_);
		}
	});
}

void ScrollerPage::onPause(AppState &state) {
	state.keybinds.unbindAll();
	destroyResources();
}

void ScrollerPage::onPop(AppState &state) {
	// Restore the original logical presentation so other pages (Home,
	// Settings, etc.) render in the design-resolution LETTERBOX space.
	SDL_SetRenderLogicalPresentation(state.renderer, savedLogicalW_,
									 savedLogicalH_, savedMode_);

	state.audio.stopTrackFadeOut(kFadeSeconds);
	state.keybinds.unbindAll();
	destroyResources();
	TTF_Quit();
}

void ScrollerPage::handleEvent(const SDL_Event &) {}

void ScrollerPage::update(float dt) {
	if (state_) {
		state_->audio.update(dt);
	}

	// Block boundaries are minute-granular, so a one-second poll is plenty and
	// avoids mutating the process timezone every frame.
	schedulePollTimer_ -= dt;
	if (schedulePollTimer_ <= 0.0f) {
		schedulePollTimer_ = 1.0f;
		pollScheduleChange();
	}

	updateAutoVelocity(dt);

	scrollOffset_ += velocity_ * dt;
	float move = std::floor(scrollOffset_);
	if (move != 0.0f) {
		scrollOffset_ -= move;
		for (auto &line : lines_) {
			for (auto &w : line.words) {
				w.y += move;
			}
		}
	}

	if (lines_.empty()) {
		return;
	}

	if (velocity_ > 0.0f) {
		// Lines move downward. Recycle every line that scrolled fully off the
		// bottom this frame (movement is continuous, so one frame can cover
		// several line heights) and add a replacement just above the top.
		while (!lines_.empty() && lines_.back().words[0].y > screenH_) {
			float baseY = lines_.front().words[0].y - lineHeight_;
			lines_.pop_back();
			if (!addLineAt(baseY)) {
				break;
			}
		}
	} else if (velocity_ < 0.0f) {
		// Lines move upward. Recycle every line that scrolled fully off the top
		// this frame and add a replacement just below the bottom.
		while (!lines_.empty() &&
			   lines_.front().words[0].y + lines_.front().words[0].height <
				   0.0f) {
			float baseY = lines_.back().words[0].y + lineHeight_;
			lines_.pop_front();
			if (!addLineAt(baseY)) {
				break;
			}
		}
	}
}

void ScrollerPage::render(SDL_Renderer *renderer) {
	SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0);
	SDL_RenderClear(renderer);

	for (const auto &line : lines_) {
		if (line.words.empty()) {
			continue;
		}
		float startX = std::floor((screenW_ - line.width) / 2.0f);
		for (const auto &w : line.words) {
			SDL_SetTextureColorMod(w.texture, line.r, line.g, line.b);
			SDL_FRect dst{startX + w.x, w.y, w.width, w.height};
			SDL_RenderTexture(renderer, w.texture, nullptr, &dst);
		}
	}
}

void ScrollerPage::buildStreams(AppState &state) {
	streams_.clear();
	fallbackPalette_.clear();
	streamIndex_ = 0;
	scheduleChangePending_ = false;

	// Schedule state: resolve the active Block from the schedule manager (which
	// owns the fetched/cached payload and the local on/off toggle). The block
	// boundary is handled in advanceStream(), so rebuilding mid-playback never
	// truncates the current proclamation.
	const radiantwave::config::AppConfig cfg = state.config.get();
	timezone_ = cfg.timezone;
	// Keep the engine's local toggle in step with config (it may have been
	// changed in System Settings or hot-reloaded).
	state.scheduleManager.setEnabled(cfg.proclamation.schedule_enabled);

	const int now = radiantwave::timezone::currentLocalMinutes(timezone_);
	const radiantwave::schedule::Weekday weekday =
		radiantwave::schedule::weekdayFromIndex(
			radiantwave::timezone::currentLocalWeekday(timezone_));
	const radiantwave::schedule::Decision decision =
		state.scheduleManager.activeBlock(now, weekday);
	scheduleActive_ = state.scheduleManager.enabled();
	if (decision.hasBlock) {
		activeBlockProclamationIds_ = decision.block.proclamation_ids;
		activeBlockDynamicAudio_ = decision.block.dynamic_audio;
		activeBlockIndex_ = 1; // any non-negative marker: a block is active
	} else {
		activeBlockProclamationIds_.clear();
		activeBlockDynamicAudio_ = false;
		activeBlockIndex_ = -1;
	}

	auto proclamations = state.db.getActiveProclamations();
	if (proclamations.empty()) {
		return;
	}

	for (const auto &c :
		 state.db.getPaletteForFrequencyId(5)) { // 528 Hz palette
		fallbackPalette_.push_back({c.r, c.g, c.b, c.a});
	}

	std::unordered_map<int, std::vector<radiantwave::scroller::StreamColor>>
		palettesByFreqId;
	for (const auto &rec : proclamations) {
		int freqId = rec.solfeggio_frequency_id;
		if (palettesByFreqId.count(freqId) != 0) {
			continue;
		}
		std::vector<radiantwave::scroller::StreamColor> colors;
		for (const auto &c : state.db.getPaletteForFrequencyId(freqId)) {
			colors.push_back({c.r, c.g, c.b, c.a});
		}
		palettesByFreqId[freqId] = std::move(colors);
	}

	std::unordered_map<int, radiantwave::db::AudioFileRecord> audioByFreqId;
	for (const auto &af : state.db.getAudioFiles()) {
		int freqId = af.solfeggio_frequency_id;
		// Self-heal for databases seeded from a legacy manifest that left the
		// frequency id at 0 for every row: recover the id from the filename.
		if (freqId == 0) {
			freqId = radiantwave::audio::frequencyIdForHz(
				radiantwave::audio::hzFromFilename(af.filename));
		}
		if (freqId != 0) {
			audioByFreqId[freqId] = af;
		}
	}

	const std::vector<std::string>* scheduledIds = nullptr;
	std::vector<std::string> scheduledOrder;
	if (activeBlockIndex_ >= 0 && !activeBlockProclamationIds_.empty()) {
		scheduledOrder = activeBlockProclamationIds_;
		scheduledIds = &scheduledOrder;
	}

	streams_ = radiantwave::scroller::buildStreams(
		proclamations, palettesByFreqId, fallbackPalette_, audioByFreqId,
		DEFAULT_PROPLEAMATION_ID, scheduledIds);
}

bool ScrollerPage::scheduleBlockActiveNow() const {
	if (!state_) {
		return false;
	}
	const int now = radiantwave::timezone::currentLocalMinutes(timezone_);
	const radiantwave::schedule::Weekday weekday =
		radiantwave::schedule::weekdayFromIndex(
			radiantwave::timezone::currentLocalWeekday(timezone_));
	return state_->scheduleManager.activeBlock(now, weekday).hasBlock;
}

void ScrollerPage::pollScheduleChange() {
	// The manager owns the local toggle; when off, there is never an active block.
	if (!state_) {
		return;
	}
	const bool activeNow = scheduleBlockActiveNow();
	const bool hadBlock = activeBlockIndex_ >= 0;
	if (activeNow != hadBlock) {
		scheduleChangePending_ = true;
	}
}

bool ScrollerPage::effectiveDynamicAudio() const {
	// dynamicAudio=true on the active block forces dynamic audio, overriding
	// whatever the device selected. false means "don't override": the device's
	// own selection (dynamic or a fixed track) applies as usual.
	if (scheduleActive_ && activeBlockIndex_ >= 0 && activeBlockDynamicAudio_) {
		return true;
	}
	return state_ ? state_->config.get().audio.dynamic_audio : false;
}

void ScrollerPage::createFont(AppState &state) {
	if (font_) {
		TTF_CloseFont(font_);
		font_ = nullptr;
	}

	// A different font or size changes every rasterized glyph, so the scrambled
	// tile atlas is invalid. clearCharTextures() also runs on pause/pop, but
	// this covers a re-entry that re-creates the font without a destroy cycle.
	clearCharTextures();

	fontPxSize_ = state.config.get().proclamation.font_size;
	if (fontPxSize_ <= 0) {
		fontPxSize_ = 32;
	}

	font_ = TTF_OpenFont("assets/fonts/Roboto-Regular.ttf", fontPxSize_);
	if (!font_) {
		return;
	}

	int w = 0;
	int h = 0;
	TTF_GetStringSize(font_, "Mg", 0, &w, &h);
	lineHeight_ =
		h > 0 ? static_cast<float>(h) : static_cast<float>(fontPxSize_);

	spaceWidth_ = measureWidth(" ");
	if (spaceWidth_ <= 0.0f) {
		spaceWidth_ = static_cast<float>(fontPxSize_) * 0.5f;
	}
}

void ScrollerPage::createPatterns() {
	patterns_.clear();
	patterns_.reserve(streams_.size());
	for (size_t i = 0; i < streams_.size(); ++i) {
		int peak = computePeakWordCount(streams_[i].words);
		patterns_.emplace_back(
			peak, maxLineWidth_, spaceWidth_,
			[this](const std::string &word) { return measureWidth(word); });
	}
}

int ScrollerPage::computePeakWordCount(
	const std::vector<std::string> &words) const {
	if (words.empty() || screenW_ <= 0.0f) {
		return 1;
	}

	// Average rendered cost of one word, including its share of inter-word
	// spacing. The peak is the number of whole words that fit across the
	// screen, so the widest Fibonacci lines fill the width at natural spacing.
	double total = 0.0;
	for (const auto &w : words) {
		total += measureWidth(w);
	}
	double n = static_cast<double>(words.size());
	double perWord = (total + (n - 1.0) * spaceWidth_) / n;
	if (perWord <= 0.0) {
		perWord = 1.0;
	}

	int fit = static_cast<int>(std::lround(screenW_ / perWord));
	return fit < 1 ? 1 : fit;
}

void ScrollerPage::destroyResources() {
	clearCharTextures();

	for (auto &entry : wordTextures_) {
		if (entry.second.texture) {
			SDL_DestroyTexture(entry.second.texture);
		}
	}
	wordTextures_.clear();

	if (font_) {
		TTF_CloseFont(font_);
		font_ = nullptr;
	}
}

void ScrollerPage::rebuildWordTextures() {
	wordTextures_.clear();
	for (auto &line : lines_) {
		float width = 0.0f;
		for (auto &item : line.words) {
			ensureWordTexture(item.text);
			const CachedWord &cached = wordTextures_[item.text];
			if (!cached.texture) {
				continue;
			}
			item.texture = cached.texture;
			item.width = cached.width;
			item.height = cached.height;
			if (width > 0.0f) {
				width += spaceWidth_;
			}
			item.x = width;
			width += item.width;
		}
		line.width = width;
	}
}

void ScrollerPage::prefillLines() {
	if (streams_.empty() || lineHeight_ <= 0.0f) {
		return;
	}

	int n = static_cast<int>(std::ceil(screenH_ / lineHeight_)) + 2;
	for (int i = 0; i < n; ++i) {
		float baseY = -lineHeight_ + static_cast<float>(i) * lineHeight_;
		addLineAt(baseY);
	}
}

bool ScrollerPage::addLineAt(float baseY) {
	if (streams_.empty() || !font_) {
		return false;
	}

	ProclamationStream &stream = streams_[streamIndex_];
	if (stream.words.empty()) {
		advanceStream();
		return false;
	}

	FibonacciLinePattern &pattern = patterns_[streamIndex_];

	// Capture palette state before any stream advance.
	std::vector<radiantwave::scroller::StreamColor> paletteCopy =
		stream.palette;
	int lineColorIndex = stream.colorIndex;
	stream.colorIndex++;

	std::vector<std::string> wordStrs;
	int placed = pattern.nextLine(stream.words, wordStrs);

	stream.wordsPlaced += placed;
	// First word of a fresh pass is the "start" of the proclamation; print to
	// stdout once so the console shows the current title while it plays.
	if (stream.wordsPlaced == placed) {
		std::printf("Playing %s\n", stream.name.c_str());
	}
	bool advanced = false;
	while (!advanced && !stream.words.empty() &&
		   stream.wordsPlaced >= static_cast<int>(stream.words.size())) {
		stream.wordsPlaced -= static_cast<int>(stream.words.size());
		stream.completed++;
		if (stream.completed >= stream.repeat) {
			stream.completed = 0;
			advanceStream();
			advanced = true;
		}
	}

	ScrollerLine line;
	float width = 0.0f;
	for (const auto &text : wordStrs) {
		ensureWordTexture(text);
		const CachedWord &cached = wordTextures_[text];
		if (!cached.texture) {
			continue;
		}
		WordItem item;
		item.text = text;
		item.texture = cached.texture;
		item.width = cached.width;
		item.height = cached.height;
		item.y = baseY;
		if (width > 0.0f) {
			width += spaceWidth_;
		}
		item.x = width;
		width += item.width;
		line.words.push_back(item);
	}

	if (line.words.empty()) {
		return false;
	}
	line.width = width;

	if (!paletteCopy.empty()) {
		const auto &c =
			paletteCopy[lineColorIndex % static_cast<int>(paletteCopy.size())];
		line.r = c.r;
		line.g = c.g;
		line.b = c.b;
	}

	if (!lines_.empty() && baseY < lines_.front().words[0].y) {
		lines_.push_front(std::move(line));
	} else {
		lines_.push_back(std::move(line));
	}
	return true;
}

void ScrollerPage::advanceStream() {
	if (streams_.empty()) {
		return;
	}
	if (scheduleChangePending_ && state_) {
		// A schedule block changed while the previous proclamation was playing.
		// Apply it only now, at a stream boundary, so the current proclamation
		// finishes instead of being cut off.
		buildStreams(*state_);
		createPatterns();
		streamIndex_ = 0;
	} else {
		streamIndex_ = (streamIndex_ + 1) % static_cast<int>(streams_.size());
	}
	if (streams_.empty()) {
		return;
	}
	// Diagnostic: report the palette the incoming stream will render so the
	// console shows whether colors should change when this stream starts.
	const ProclamationStream &stream = streams_[streamIndex_];
	if (!stream.palette.empty()) {
		const auto &c = stream.palette[0];
		std::printf("[Scroller] -> %s freqId=%d palette[0]=#%02X%02X%02X\n",
					stream.name.c_str(), stream.solfeggio_frequency_id, c.r,
					c.g, c.b);
	} else {
		std::printf("[Scroller] -> %s freqId=%d palette=EMPTY\n",
					stream.name.c_str(), stream.solfeggio_frequency_id);
	}
	switchAudioForCurrentStream();
}

void ScrollerPage::switchAudioForCurrentStream() {
	if (prefilling_ || streams_.empty() || !state_) {
		return;
	}

	// Dynamic audio only: with a fixed manual track selected the audio must
	// never switch as proclamations change. An active schedule block's
	// dynamicAudio flag overrides the device-wide setting.
	if (!effectiveDynamicAudio()) {
		return;
	}

	const ProclamationStream &stream = streams_[streamIndex_];
	if (stream.solfeggio_frequency_id == 0 || stream.audioFilename.empty()) {
		return; // default stream: never touch audio
	}
	if (!std::filesystem::exists(audioFilePath(stream.audioFilename))) {
		return; // keep current track; retried on the next activation
	}
	// Crossfades over kFadeSeconds; a no-op when the requested track is the
	// same one already playing.
	state_->audio.playTrackCrossfade(stream.audioFilename, kFadeSeconds);
}

void ScrollerPage::updateAutoVelocity(float dt) {
	switch (velocityState_) {
	case 0: // ramping to the negative extreme
		velocity_ -= velocityStep_ * dt;
		if (velocity_ <= kVelocityMin) {
			velocity_ = kVelocityMin;
			velocityTimer_ = velocityDelay_;
			velocityState_ = 1;
		}
		break;
	case 1: // holding at the negative extreme
		velocityTimer_ -= dt;
		if (velocityTimer_ <= 0.0f) {
			velocityState_ = 2;
		}
		break;
	case 2: // ramping to the positive extreme
		velocity_ += velocityStep_ * dt;
		if (velocity_ >= kVelocityMax) {
			velocity_ = kVelocityMax;
			velocityTimer_ = velocityDelay_;
			velocityState_ = 3;
		}
		break;
	case 3: // holding at the positive extreme
		velocityTimer_ -= dt;
		if (velocityTimer_ <= 0.0f) {
			velocityState_ = 0;
		}
		break;
	default:
		velocityState_ = 0;
		break;
	}
}

void ScrollerPage::ensureWordTexture(const std::string &word) {
	if (wordTextures_.count(word) != 0) {
		return;
	}

	// Proclamation text is never rendered as human-readable type
	// ([This implementation] rendering pipeline). Each word is assembled from
	// per-glyph scrambled tiles instead:
	//   1. split the word into code points (utf8_utils.h) -- letters, digits,
	//      and common punctuation such as ` , ' " . - all get their own tile;
	//   2. each code point's glyph is rasterized once, permuted into an N x N
	//      tile by the Fibonacci affine map
	//      (scramble/fibonacci_scrambler.h), and cached in charTextures_
	//      keyed by the glyph string (one scramble per code point per font
	//      size, amortized O(N^2 * rounds));
	//   3. the word surface is built by blitting each tile's top-left
	//      glyphW x glyphH crop (the crop-window convention) at the glyph's
	//      advance position.
	// Scrambling is per glyph rather than per word so a single tile serves
	// every occurrence of a code point across the whole proclamation set.
	// Word layout widths still come from TTF_GetStringSize(), so line
	// breaking, centering, and the Fibonacci line pattern are unchanged; only
	// the glyph pixels move.
	CachedWord cached;
	if (font_ && state_) {
		std::vector<uint32_t> codePoints;
		if (radiantwave::splitUtf8(word, codePoints) && !codePoints.empty()) {
			std::vector<CharEntry *> glyphs;
			float totalWidth = 0.0f;
			float glyphHeight = 0.0f;
			for (uint32_t cp : codePoints) {
				const std::string glyphText = radiantwave::encodeUtf8(cp);
				if (glyphText.empty()) {
					continue;
				}
				ensureCharTexture(glyphText);
				CharEntry &entry = charTextures_[glyphText];
				if (!entry.surface) {
					continue;
				}
				glyphs.push_back(&entry);
				totalWidth += entry.advance;
				if (entry.glyphH > glyphHeight) {
					glyphHeight = entry.glyphH;
				}
			}

			if (!glyphs.empty()) {
				const int wordW =
					std::max(1, static_cast<int>(std::lround(totalWidth)));
				const int wordH =
					std::max(1, static_cast<int>(std::lround(glyphHeight)));
				SDL_Surface *wordSurface =
					SDL_CreateSurface(wordW, wordH, SDL_PIXELFORMAT_RGBA8888);
				if (wordSurface) {
					// Every glyph surface carries the font's full line height
					// (probe-verified), so y = 0 keeps every crop on the shared
					// baseline and per-word textures stay line-height tall.
					float x = 0.0f;
					for (const CharEntry *entry : glyphs) {
						SDL_Rect srcRect{0, 0, static_cast<int>(entry->glyphW),
										 static_cast<int>(entry->glyphH)};
						SDL_Rect dstRect{static_cast<int>(std::lround(x)), 0,
										 static_cast<int>(entry->glyphW),
										 static_cast<int>(entry->glyphH)};
						SDL_BlitSurface(entry->surface, &srcRect, wordSurface,
										&dstRect);
						x += entry->advance;
					}
					cached.texture = SDL_CreateTextureFromSurface(
						state_->renderer, wordSurface);
					// The scroller steps glyphs in whole pixels, so bilinear
					// filtering can only smear them: nearest-neighbor keeps
					// every frame pixel-sharp.
					if (cached.texture) {
						SDL_SetTextureScaleMode(cached.texture,
												SDL_SCALEMODE_NEAREST);
					}
					cached.width = static_cast<float>(wordSurface->w);
					cached.height = static_cast<float>(wordSurface->h);
					SDL_DestroySurface(wordSurface);
					if (!cached.texture) {
						cached.width = 0.0f;
						cached.height = 0.0f;
					}
				}
			}
		}
	}
	wordTextures_[word] = cached;
}

void ScrollerPage::ensureCharTexture(const std::string &glyph) {
	if (charTextures_.count(glyph) != 0) {
		return;
	}

	// Rasterize, scramble, and cache one glyph tile. `charTextures_` is keyed
	// on the glyph's UTF-8 text, so a code point is scrambled at most once per
	// font size; createFont() clears the atlas whenever the font or its size
	// changes, and pause/pop clear it as part of destroyResources().
	CharEntry entry;
	if (font_ && state_) {
		SDL_Surface *surface = TTF_RenderText_Blended(font_, glyph.c_str(), 0,
													  {255, 255, 255, 255});
		if (surface) {
			const int gW = surface->w;
			const int gH = surface->h;
			const int n = radiantwave::scramble::canvasSize(gW, gH);
			if (n > 0) {
				// The scrambler needs tightly packed RGBA8888; a TTF surface's
				// pitch can exceed gW * 4, so copy row by row.
				std::vector<uint8_t> source(static_cast<size_t>(gW) * gH * 4);
				const uint8_t *pixels =
					static_cast<const uint8_t *>(surface->pixels);
				for (int y = 0; y < gH; ++y) {
					std::memcpy(source.data() + static_cast<size_t>(y) * gW * 4,
								pixels +
									static_cast<size_t>(y) * surface->pitch,
								static_cast<size_t>(gW) * 4);
				}

				std::vector<uint8_t> scrambled(static_cast<size_t>(n) * n * 4);
				// Default key: compile-time seed (kDefaultSeed) and 4 rounds.
				// The fixed seed makes every device render the same glyph as
				// the same scrambled pattern, with no key to persist or ship.
				radiantwave::scramble::ScrambleConfig config;
				if (radiantwave::scramble::scramble(
						source.data(), scrambled.data(), gW, gH, config)) {
					SDL_Surface *tile =
						SDL_CreateSurface(n, n, SDL_PIXELFORMAT_RGBA8888);
					if (tile) {
						uint8_t *dst = static_cast<uint8_t *>(tile->pixels);
						for (int y = 0; y < n; ++y) {
							std::memcpy(dst + static_cast<size_t>(y) *
												  tile->pitch,
										scrambled.data() +
											static_cast<size_t>(y) * n * 4,
										static_cast<size_t>(n) * 4);
						}
						entry.surface = tile;
						entry.glyphW = static_cast<float>(gW);
						entry.glyphH = static_cast<float>(gH);
						entry.advance = measureWidth(glyph);
						if (entry.advance <= 0.0f) {
							entry.advance = entry.glyphW;
						}
					}
				}
			}
			SDL_DestroySurface(surface);
		}
	}
	charTextures_[glyph] = entry;
}

void ScrollerPage::clearCharTextures() {
	for (auto &entry : charTextures_) {
		if (entry.second.surface) {
			SDL_DestroySurface(entry.second.surface);
		}
	}
	charTextures_.clear();
}

float ScrollerPage::measureWidth(const std::string &text) const {
	if (!font_) {
		return 0.0f;
	}
	int w = 0;
	int h = 0;
	TTF_GetStringSize(font_, text.c_str(), 0, &w, &h);
	return static_cast<float>(w);
}

std::string ScrollerPage::audioFilePath(const std::string &filename) const {
	std::string path1 =
		std::string(std::getenv("HOME") ? std::getenv("HOME") : "/tmp") +
		"/.local/radiantwave/audio/" + filename;
	std::string path2 = "assets/audio/" + filename;
	return std::filesystem::exists(path1) ? path1 : path2;
}