Method GetCharPosition

src/gfx_layout.cpp:237–295

* Get the position of a character in the layout. * @param ch Character to get the position of. Must be an iterator of the string passed to the constructor. * @return Upper left corner of the character relative to the start of the string. * @note Will only work right for single-line strings. */

 * @note Will only work right for single-line strings.
 */
ParagraphLayouter::Position Layouter::GetCharPosition(std::string_view::const_iterator ch) const
{
	const auto &line = this->front();

	/* Pointer to the end-of-string marker? Return total line width. */
	if (ch == this->string.end()) {
		Point p = {_current_text_dir == TD_LTR ? line->GetWidth() : 0, 0};
		return p;
	}

	/* Initial position, returned if character not found. */
	const ParagraphLayouter::Position initial_position = Point{_current_text_dir == TD_LTR ? 0 : line->GetWidth(), 0};

	/* Find the code point index which corresponds to the char
	 * pointer into our UTF-8 source string. */
	size_t index = 0;
	{
		Utf8View view(this->string);
		const size_t offset = ch - this->string.begin();
		const auto pos = view.GetIterAtByte(offset);

		/* We couldn't find the code point index. */
		if (pos.GetByteOffset() != offset) return initial_position;

		for (auto it = view.begin(); it < pos; ++it) {
			char32_t c = *it;
			if (!IsConsumedFormattingCode(c)) index += line->GetInternalCharLength(c);
		}
	}

	const ParagraphLayouter::Position *position = &initial_position;

	/* Scan all runs until we've found our code point index. */
	size_t best_index = SIZE_MAX;
	for (int run_index = 0; run_index < line->CountRuns(); run_index++) {
		const ParagraphLayouter::VisualRun &run = line->GetVisualRun(run_index);
		const auto &positions = run.GetPositions();
		const auto &charmap = run.GetGlyphToCharMap();

		auto itp = positions.begin();
		for (auto it = charmap.begin(); it != charmap.end(); ++it, ++itp) {
			const size_t cur_index = static_cast<size_t>(*it);
			/* Found exact character match? */
			if (cur_index == index) return *itp;

			/* If the character we are looking for has been combined with other characters to form a ligature then
			 * we may not be able to find an exact match. We don't actually know if our character is part of a
			 * ligature. In this case we will aim to select the first character of the ligature instead, so the best
			 * index is the index nearest to but lower than the desired index. */
			if (cur_index < index && (best_index < cur_index || best_index == SIZE_MAX)) {
				best_index = cur_index;
				position = &*itp;
			}
		}
	}

	/* At the end of the run but still didn't find our character so probably a trailing ligature, use the last found position. */
	return *position;