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Enhance line breaking logic with detailed comments for clarity and maintainability

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This commit is contained in:
Arthur Tazhitdinov 2025-12-26 01:54:43 +05:00
parent 73c8b17737
commit 4ee9783e49
1 changed files with 18 additions and 5 deletions
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23
lib/Epub/Epub/ParsedText.cpp
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@ -166,10 +166,14 @@ std::vector<size_t> ParsedText::computeLineBreaks(const GfxRenderer& renderer, c
auto runDp = [&](std::vector<size_t>& lineBreaks) { auto runDp = [&](std::vector<size_t>& lineBreaks) {
const size_t totalWordCount = wordWidths.size(); const size_t totalWordCount = wordWidths.size();
// DP table to store the minimum badness (cost) of lines starting at index i
std::vector<int> dp(totalWordCount); std::vector<int> dp(totalWordCount);
// 'ans[i]' stores the index 'j' of the *last word* in the optimal line starting at 'i'
std::vector<size_t> ans(totalWordCount); std::vector<size_t> ans(totalWordCount);
// Base Case
dp[totalWordCount - 1] = 0; dp[totalWordCount - 1] = 0;
ans[totalWordCount - 1] = totalWordCount - 1; ans[totalWordCount - 1] = totalWordCount - 1;
@ -178,6 +182,7 @@ std::vector<size_t> ParsedText::computeLineBreaks(const GfxRenderer& renderer, c
dp[i] = MAX_COST; dp[i] = MAX_COST;
for (size_t j = i; j < totalWordCount; ++j) { for (size_t j = i; j < totalWordCount; ++j) {
// Current line length: previous width + space + current word width
currlen += wordWidths[j] + spaceWidth; currlen += wordWidths[j] + spaceWidth;
if (currlen > pageWidth) { if (currlen > pageWidth) {
@ -200,13 +205,14 @@ std::vector<size_t> ParsedText::computeLineBreaks(const GfxRenderer& renderer, c
cost = 0; cost = 0;
} else { } else {
const int remainingSpace = pageWidth - currlen; const int remainingSpace = pageWidth - currlen;
// Use long long for the square to prevent overflow
const long long cost_ll = static_cast<long long>(remainingSpace) * remainingSpace + dp[j + 1]; const long long cost_ll = static_cast<long long>(remainingSpace) * remainingSpace + dp[j + 1];
cost = cost_ll > MAX_COST ? MAX_COST : static_cast<int>(cost_ll); cost = cost_ll > MAX_COST ? MAX_COST : static_cast<int>(cost_ll);
} }
if (cost < dp[i]) { if (cost < dp[i]) {
dp[i] = cost; dp[i] = cost;
ans[i] = j; ans[i] = j; // j is the index of the last word in this optimal line
} }
} }
} }
@ -222,6 +228,7 @@ std::vector<size_t> ParsedText::computeLineBreaks(const GfxRenderer& renderer, c
} }
}; };
// Stores the index of the word that starts the next line (last_word_index + 1)
std::vector<size_t> lineBreakIndices; std::vector<size_t> lineBreakIndices;
while (true) { while (true) {
@ -307,19 +314,22 @@ void ParsedText::extractLine(const size_t breakIndex, const int pageWidth, const
const size_t lastBreakAt = breakIndex > 0 ? lineBreakIndices[breakIndex - 1] : 0; const size_t lastBreakAt = breakIndex > 0 ? lineBreakIndices[breakIndex - 1] : 0;
const size_t lineWordCount = lineBreak - lastBreakAt; const size_t lineWordCount = lineBreak - lastBreakAt;
// Calculate total word width for this line
int lineWordWidthSum = 0; int lineWordWidthSum = 0;
for (size_t idx = lastBreakAt; idx < lineBreak; ++idx) { for (size_t i = lastBreakAt; i < lineBreak; i++) {
lineWordWidthSum += wordWidths[idx]; lineWordWidthSum += wordWidths[i];
} }
const bool isLastLine = breakIndex == lineBreakIndices.size() - 1;
// Calculate spacing
const int spareSpace = pageWidth - lineWordWidthSum; const int spareSpace = pageWidth - lineWordWidthSum;
int spacing = spaceWidth; int spacing = spaceWidth;
const bool isLastLine = breakIndex == lineBreakIndices.size() - 1;
if (style == TextBlock::JUSTIFIED && !isLastLine && lineWordCount >= 2) { if (style == TextBlock::JUSTIFIED && !isLastLine && lineWordCount >= 2) {
spacing = spareSpace / (lineWordCount - 1); spacing = spareSpace / (lineWordCount - 1);
} }
// Calculate initial x position
uint16_t xpos = 0; uint16_t xpos = 0;
if (style == TextBlock::RIGHT_ALIGN) { if (style == TextBlock::RIGHT_ALIGN) {
xpos = spareSpace - (lineWordCount - 1) * spaceWidth; xpos = spareSpace - (lineWordCount - 1) * spaceWidth;
@ -327,6 +337,7 @@ void ParsedText::extractLine(const size_t breakIndex, const int pageWidth, const
xpos = (spareSpace - (lineWordCount - 1) * spaceWidth) / 2; xpos = (spareSpace - (lineWordCount - 1) * spaceWidth) / 2;
} }
// Pre-calculate X positions for words
std::list<uint16_t> lineXPos; std::list<uint16_t> lineXPos;
for (size_t i = lastBreakAt; i < lineBreak; i++) { for (size_t i = lastBreakAt; i < lineBreak; i++) {
const uint16_t currentWordWidth = wordWidths[i]; const uint16_t currentWordWidth = wordWidths[i];
@ -334,11 +345,13 @@ void ParsedText::extractLine(const size_t breakIndex, const int pageWidth, const
xpos += currentWordWidth + spacing; xpos += currentWordWidth + spacing;
} }
// Iterators always start at the beginning as we are moving content with splice below
auto wordEndIt = words.begin(); auto wordEndIt = words.begin();
auto wordStyleEndIt = wordStyles.begin(); auto wordStyleEndIt = wordStyles.begin();
std::advance(wordEndIt, lineWordCount); std::advance(wordEndIt, lineWordCount);
std::advance(wordStyleEndIt, lineWordCount); std::advance(wordStyleEndIt, lineWordCount);
// *** CRITICAL STEP: CONSUME DATA USING SPLICE ***
std::list<std::string> lineWords; std::list<std::string> lineWords;
lineWords.splice(lineWords.begin(), words, words.begin(), wordEndIt); lineWords.splice(lineWords.begin(), words, words.begin(), wordEndIt);
std::list<EpdFontStyle> lineWordStyles; std::list<EpdFontStyle> lineWordStyles;