Method GetCharAtPosition

src/gfx_layout.cpp:303–339

* 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. */

 * @return String offset of the position (bytes) or -1 if no character is at the position.
 */
ptrdiff_t Layouter::GetCharAtPosition(int x, size_t line_index) const
{
	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);
		const auto &glyphs = run.GetGlyphs();
		const auto &positions = run.GetPositions();
		const auto &charmap = run.GetGlyphToCharMap();

		for (int i = 0; i < run.GetGlyphCount(); i++) {
			/* Not a valid glyph (empty). */
			if (glyphs[i] == 0xFFFF) continue;

			int begin_x = positions[i].left;
			int end_x   = positions[i].right + 1;

			if (IsInsideMM(x, begin_x, end_x)) {
				/* Found our glyph, now convert to UTF-8 string index. */
				size_t index = charmap[i];

				size_t cur_idx = 0;
				Utf8View view(this->string);
				for (auto it = view.begin(), end = view.end(); it != end; ++it) {
					if (cur_idx == index) return it.GetByteOffset();

					char32_t c = *it;
					if (!IsConsumedFormattingCode(c)) cur_idx += line->GetInternalCharLength(c);
				}
			}
		}
	}

	return -1;
}

/**
 * Get a static font instance.