Java Game Development - 26 - Watching the Sprite Move Video Lecture | How to create Games in Java - Gaming Development - Software Development

what is going on guys welcome to your
26th java game development tutorial and
in this story we're finally gonna finish
up the stupid spray and actually why
shouldn't move around the screen so
before I get started this store I just
want to vent to you guys a little bit
because I just got back from downtown
Raleigh where I had an appointment and I
actually had to park my car in some
weird place to make sure I got to my
appointment outside because I couldn't
find a parking spot and when I came out
I forgot where I parked it because I'm
not familiar with downtown Raleigh so I
had to walk around downtown Raleigh for
about an hour and a half up and down
every street until I found my car and uh
yeah it was pretty annoying but now that
I am done venting I will finish this
tutorial so let's go ahead and make the
method update because remember we're
going to air up here it says create
method update all right you talked me
into it update um sprites positioning
and all this is going to do is check if
the sprite is off the screen and if it
goes off the screen is going to put it
back on the screen now let's go ahead
and name public void update in long time
past and we're going to use this time
passed one time in the final update so
that's pretty cool so now that before we
start building this method I need to
tell you guys about one thing now
whenever we have any image we're working
with the image is actually a box it's
has a width and it has a height now
there are a lot of pixels in the image
so when you're testing what part of it
goes off the screen java only cares
about the top left portion of that image
so that would be zero zero of the image
since it doesn't care about the bottom
right top right it only cares whenever
we're testing if this sprays off the
screen it only is going to look at the
top left portion of the image so that's
a little thing that you want to keep in
mind so and you'll see why this is
useful later on but what we want to test
first thing at the spray well we want to
test where it is
if sprite dot get X which means it's x
value is less than zero which means if
its leftmost side of the spray is less
than 0 well 0 is the left more left most
part of your screen
because remember top left to 0 0 so if
this your spray is less than 0 its X
positioning it means it must be off to
the left hand side off your screen
somewhere so what do we want to do if it
goes off your screen past 0 like a
negative 5 or negative 10 that that's
when this would be true but what we want
to do is we want to set the speed
because here's what must happen if it
got off the screen to your left
somewhere then when it was going from
right to left it must have just never
stopped its speed or velocity and just
kept going left so we want to just
change the velocity to the same exact
velocity but we wanted to go left to
right instead of right to left so it
stays in your viewing area so let's go
ahead and put a sprite dot set velocity
of X because remember that's what we're
checking right now and what we want to
do is we want to get the absolute value
because if you remember from math class
absolute value is always positive no
matter what so the absolute value of
negative 10 is 10 absolute value of 9 is
9 of negative 32 is 32 again it takes
any number and makes it positive so math
dot absolute value and in your absolute
value just type sprite how fast you
wanted to go well just get those old
velocities before because that was good
enough so what this pretty much does is
if your sprite went off your screen to
the left hand side it must have been
going from right to left until it
finally just went off into lala land so
what this does is it just changes its
velocity and reverses it so it goes back
from left to right and destruction so we
need to do this for um the let's see the
X and we need to do this for else if
now else is come on Hoss else if sprite
dot get X and we need to do plus sprite
dot get width and remember that X is the
top left portion of your image so if you
have X plus the width it would be the
right corner you get it and let me try
to explain when we're done with this but
in other words you're always whenever
you do get X it says give me the top
left or excuse me the left side of your
image so if you have the left side plus
the width it's there for the right side
so um just think about it and I guess
that's as best as I can explain it and
then what do you need to do for this if
this is greater than the screens dot
screens that get width right there what
do we want to do so if this the right
side of our image is greater than or
again but greater than or equal to does
it really matter
the screens width that means if the
right side of your image surpasses or
goes past the right side of your screen
so therefore that part of the image is
not visible what do we want to do well
we wanted to do the same thing so
actually we can just go ahead and copy
this we want to set it's a velocity but
instead of having a positive velocity
and this means left to right it's
getting bigger and bigger we want to
have a negative velocity so negative
absolute value right there and let's see
how much time I have left five minutes
not bad so this pretty much says all
right at the left side of your images or
suit if the left side of your image goes
off the screen to the left give it a
positive velocity if the right side of
your image or spray goes off the right
side of your screen then give it a
negative velocity to keep it moving this
way so now all we have to do is change
this for y so just copy this whole thing
remind you do sprite get why is less
than zero Sprint's the philosophy why
absolute value get philosophy why also
spray get why get height because
remember why is up and down so you're
not testing for width anymore you
testing for height of your screen get
height and set why and get why and let
me make sure I didn't mess anything up
and if I did I'll correct there later
but all you need to do is this checks um
if it goes off the screen left and right
and this checks if it goes off the
screen up and down and if does it
corrects it accordingly so now the only
thing we need to do is update the
spreads position using sprite the update
and remember this update sprite the
update is the update in this class
wherever we put it right there it
updates the spray position based on how
much time has passed so let's go ahead
and spray update and pass in time and
unless we forgot a Y or a height or
anything
this should work so I know you guys
can't see it but let's go ahead and run
this and I'll tell you guys what's
happening yep my sprite is bouncing
around my screen in all kinds of
directions and when it hits one of the
corners of my screen set it hit this top
corner it bounces this way and when it
hits this corner it bounces this way and
this erected me side I mean not corner
it bounces like this and as soon as it
gets to the top left bottom or right
size of your screen it just bounces off
and that's because it when it gets to
the one of those sides of screen and one
of those sides of your image exceeds the
in bounds portion it changes its
velocity so you guys need to see it and
once you see it I mean again I'm sorry
that you guys can't see on my screen
recorder but that's just how it works
once you guys see it for yourself in
code this you'll under
and perfectly how this is working but
for now I just want to thank you guys
for staying subscribe and thank you guys
for watching and make sure to check out
my next tutorials where we will be going
over some other cool stuff but I am
going to probably go to school and go to
McDonald's and eat like five double
cheeseburgers again for watching don't
forget to subscribe and I'll see you
next time