Game Programming Using Qt

Time for action – moving the background

Now the question is how to move them at different speeds. The solution is quite simple: the slowest one, the sky, is the smallest image. The fastest background, the ground and the grass, are the largest images. Now when we have a look at the end of the movePlayer() function's slot we see this:

qreal ff = qMin(1.0, m_skippedMoving/(m_fieldWidth - width()));
m_sky->setPos(-(m_sky->boundingRect().width() - width()) * ff, 0);
m_grass->setPos(-(m_grass->boundingRect().width() - width()) * ff, m_grass->y());
m_trees->setPos(-(m_trees->boundingRect().width() - width()) * ff, m_trees->y());
m_ground->setPos(-(m_ground->boundingRect().width() - width()) * ff, m_ground->y());

What just happened?

What are we doing here? ...