C++ GUI Programming with Qt 4, Second Edition 中chap05 plotter 問題 [复制链接]

這個是"雙緩沖"技術裏面的一個函數,我還是讀不明白裏面幾個變量的含義,請各位指教
void Plotter::mouseReleaseEvent(QMouseEvent *event)下面的
{...
        double dx = prevSettings.spanX() / (width() - 2 * Margin);
        double dy = prevSettings.spanY() / (height() - 2 * Margin);
        settings.minX = prevSettings.minX + dx * rect.left();
        settings.maxX = prevSettings.minX + dx * rect.right();
        settings.minY = prevSettings.maxY - dy * rect.bottom();
        settings.maxY = prevSettings.maxY - dy * rect.top();
...
}
dx  dy 是什麽呢?


感謝!

dx 是每像素点对应的数曲线宽度，dy是每像素点对应的曲线高度