A test example for https://codereview.qt-project.org/148563

cursor.cpp

#include <QtGui/QFont>
#include <QtWidgets/QApplication>
#include <QtWidgets/QTextEdit>

int main(int argc, char **argv) {
  QApplication app(argc, argv);
  QTextEdit edit;

  edit.resize(640, 480);
  edit.setHtml(
    "<p style=\"background-color: white;\">"
    " <span style=\"color: black\">black</span>"
    " <span style=\"color: darkred;\">darkred</span>"
    " <span style=\"color: darkgreen;\">darkgreen</span>"
    " <span style=\"color: darkblue;\">darkblue</span>"
    "</p>"
    "<p style=\"background-color: black;\">"
    " <span style=\"color: white\">white</span>"
    " <span style=\"color: #ff9999;\">lightred</span>"
    " <span style=\"color: lightgreen;\">lightgreen</span>"
    " <span style=\"color: lightblue;\">lightblue</span>"
    "</p>"
    "<p style=\"color: black;\">"
    " <span style=\"background-color: #ff9999;\">black on red</span>"
    " <span style=\"background-color: lightgreen;\">black on green</span>"
    " <span style=\"background-color: lightblue;\">black on blue</span>"
    "</p>"
    "<p style=\"color: white;\">"
    " <span style=\"background-color: darkred;\">white on red</span>"
    " <span style=\"background-color: darkgreen;\">white on green</span>"
    " <span style=\"background-color: darkblue;\">white on blue</span>"
    "</p>"
  );

  edit.setFont(QFont("monospace", 18));
  QFontMetrics metrics = edit.fontMetrics();
  edit.setCursorWidth(metrics.width(' '));
  edit.show();

  return app.exec();
}