fix: render <br> between paragraphs as a visible section break (#2548)

Co-authored-by: Brooks Ilg <brooksmilg@gmail.com>

lib/Epub/Epub/blocks/BlockStyle.h

@@ -32,6 +32,11 @@ struct BlockStyle {
   bool isRtl = false;              // true if resolved direction is RTL
   bool directionDefined = false;   // true if direction was explicitly set in CSS/HTML
 
+  // Set when this block was created by a <br> element. Used by startNewTextBlock to inject
+  // a full line-height gap when the <br> block stays empty (section-break use case).
+  // NOT propagated through getCombinedBlockStyle so it can't leak into sibling blocks.
+  bool fromBrElement = false;
+
   // Combined insets (margin + padding)
   [[nodiscard]] int16_t leftInset() const { return marginLeft + paddingLeft; }
   [[nodiscard]] int16_t rightInset() const { return marginRight + paddingRight; }
@@ -92,6 +97,9 @@ struct BlockStyle {
       result.directionDefined = true;
     }
 
+    // fromBrElement is consumed by startNewTextBlock when an empty <br> block
+    // is merged with the following paragraph; never propagate it further.
+    result.fromBrElement = false;
     return result;
   }
 

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -239,7 +239,16 @@ void ChapterHtmlSlimParser::startNewTextBlock(const BlockStyle& blockStyle) {
       // open. Merge those into the new style so the first child in a container inherits
       // the container's vertical spacing.
       const auto style = currentTextBlock->getBlockStyle();
-      currentTextBlock->setBlockStyle(style.getCombinedBlockStyle(blockStyle, BlockStyle::CombineAxis::Vertical));
+      BlockStyle incoming = blockStyle;
+      if (style.fromBrElement) {
+        // The empty block was created by a <br> section separator. Inject a full line of
+        // blank space before the following paragraph so the scene/section break is visible.
+        // This only fires when the <br> block stayed empty (i.e. no inline text was added).
+        const int16_t lineHeight = static_cast<int16_t>(renderer.getLineHeight(fontId) * lineCompression + 0.5f);
+        incoming.marginTop = static_cast<int16_t>(incoming.marginTop + lineHeight);
+      }
+
+      currentTextBlock->setBlockStyle(style.getCombinedBlockStyle(incoming, BlockStyle::CombineAxis::Vertical));
 
       flushPendingAnchor();
       return;
@@ -855,7 +864,14 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
         // flush word preceding <br/> to currentTextBlock before calling startNewTextBlock
         self->flushPartWordBuffer();
       }
-      self->startNewTextBlock(self->blockStyleStack.back().withoutBottom());
+      // Tag the new block so startNewTextBlock can inject a full line-height gap if
+      // the block remains empty (i.e. <br> is a section separator between paragraphs).
+      // If the block gets text added before the next block opens it becomes non-empty,
+      // goes through makePages() normally, and the flag has no effect (inline <br> case).
+      BlockStyle brStyle =
+          self->currentTextBlock ? self->currentTextBlock->getBlockStyle() : self->blockStyleStack.back();
+      brStyle.fromBrElement = true;
+      self->startNewTextBlock(brStyle);
     } else {
       self->currentCssStyle = cssStyle;
       const auto accumulated = self->blockStyleStack.back().getCombinedBlockStyle(userAlignmentBlockStyle,