Why is movement logic inverted for y axis?

[firepro20]

I am following the book SFML Game Development, and noticed to go up or down, logic is inverted.

sf::Vector2f movement(0.f, 0.f);
   if (mIsMovingUp)
      movement.y -= PlayerSpeed;
   if (mIsMovingDown)
      movement.y += PlayerSpeed;

And it works!

Is there a reason for this? Thanks in advance

[G.]

It's just convention, and it's not unusual. In SFML the y axis increases downwards.

[firepro20]

Ok thanks did not know that!