自由调整的心形

/* 当窗口大小发生变化时，触发重绘事件。 */
void resizeEvent(QResizeEvent *)
{
    update();
}

/* 画心形 */
void paintEvent(QPaintEvent *)
{
    float scale = 1;
    if (width() > height()) {
        scale = height()/28.9233;
    }
    else {
        scale = width()/32.0;
    }

    QPainter painter(this);
    painter.translate(width()/2, (height() - scale * 5.0767)/2);
    painter.setRenderHint(QPainter::Antialiasing);

    painter.setPen(Qt::NoPen);
    painter.setBrush(QBrush(Qt::red));

    QVector<QPointF> lines;
    for (float t = 0; t < 2 * M_PI; t += 0.001) {
        float x = 16 * pow(sinf(t), 3); // -16 <= x <= 16
        float y = 13 * cosf(t) - 5 * cosf(2 *t) - 2 * cosf(3 * t) - cosf(4 * t); // -17 <= y <= 11.9233
        lines.append(QPointF(x*scale, -y*scale));
    }

    painter.drawPolygon(lines);
}