Change: Text Layouter support querying all lines for character at pixel

src/gfx.cpp

@@ -899,7 +899,7 @@ ptrdiff_t GetCharAtPosition(std::string_view str, int x, FontSize start_fontsize
 	if (x < 0) return -1;
 
 	Layouter layout(str, INT32_MAX, TC_FROMSTRING, start_fontsize);
-	return layout.GetCharAtPosition(x);
+	return layout.GetCharAtPosition(x, 0);
 }
 
 /**

src/gfx_layout.cpp

@@ -270,11 +270,14 @@ Point Layouter::GetCharPosition(std::string_view::const_iterator ch) const
 /**
  * Get the character that is at a pixel position in the first line of the layouted text.
  * @param x Position in the string.
+ * @param line_index Which line of the layout to search
  * @return String offset of the position (bytes) or -1 if no character is at the position.
  */
-ptrdiff_t Layouter::GetCharAtPosition(int x) const
+ptrdiff_t Layouter::GetCharAtPosition(int x, size_t line_index) const
 {
-	const auto &line = this->front();
+	if (line_index >= this->size()) return -1;
+
+	const auto &line = this->at(line_index);
 
 	for (int run_index = 0; run_index < line->CountRuns(); run_index++) {
 		const ParagraphLayouter::VisualRun &run = line->GetVisualRun(run_index);

src/gfx_layout.h

@@ -177,7 +177,7 @@ public:
 	Layouter(std::string_view str, int maxw = INT32_MAX, TextColour colour = TC_FROMSTRING, FontSize fontsize = FS_NORMAL);
 	Dimension GetBounds();
 	Point GetCharPosition(std::string_view::const_iterator ch) const;
-	ptrdiff_t GetCharAtPosition(int x) const;
+	ptrdiff_t GetCharAtPosition(int x, size_t line_index) const;
 
 	static void ResetFontCache(FontSize size);
 	static void ResetLineCache();