<!DOCTYPE html> <meta charset="UTF-8"> <style> body { padding: 0; margin: 0; font-size: 2px; line-height: 1; } </style> <body> <script> // This is the constant in nsTextFrame.cpp of the number of lines // which a text run can be built up to. const NUM_LINES_TO_BUILD_TEXT_RUNS = 200; // Since the font-size is small, we need lots of blocks so that it can // be seen clearer whether difference is fuzzy or real failure. let x = '\u2588'.repeat(100) + '<br>'; for (let i = 0; i < NUM_LINES_TO_BUILD_TEXT_RUNS / 2 - 1; i++) { document.write(x) } // We want this piece to be in whatever place inside the first // NUM_LINES_TO_BUILD_TEXT_RUNS lines. document.write('あ\nあ<br>'); // And we want another NUM_LINES_TO_BUILD_TEXT_RUNS lines to check. for (let i = 0; i < NUM_LINES_TO_BUILD_TEXT_RUNS * 1.5; i++) { document.write(x) } </script>