GAMES

[ MAKE GAMES WITH PYTHON ]
First, on line 52, we check to see whether our square is travelling
upwards at a speed greater than 1 pixel per frame. If it is, then we
multiply that value by 0.9 so it will eventually come to a point where it
is travelling less than 1 pixel per second; when that happens, we set the
value to 0 so that we can start falling back to the bottom of the screen.
Next, our code checks whether or not our square is in the air: if it is, it
will need to come back down. On lines 59-61, we check that the square
is in the air and then start adding the gravity value to the playerVY
value; this will make our square move back down to the bottom of the
screen. Each time we add the gravity value to the playerVY value, we
multiply the former by 1.1; this makes the square speed up as it falls
back to the bottom of the screen, just as it would if you threw a ball in
the air. Lines 63-64 reset the gravity and playerVY values when the
bottom of the square hits the bottom of the screen. Lines 68-70 are fun,
in that they stop the square from moving any faster left or right once our
square has jumped in the air. You can’t change direction after you jump;
you can only change direction when you hit the ground again, so that’s
what our square does too.
Above A
demonstration
of the varying
effects of the
X velocity
when jumping
Pygame mouse events
That’s enough of the keyboard for now; it’s time for the mouse to
shine. The mouse is a simple bit of kit, so the code for it is far less
complicated than our keyboard code. If you copy out mouse.py and run
it, you’ll see a familiar red square sitting at the bottom of the screen.
Pressing your keyboard keys will do nothing this time, for this square is
different. If you want to move it, you’ve got to use the mouse to pick it
up. Drag your mouse over the square, hold down the left mouse button
[ Taking Control of the Keyboard & Mouse ]
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