Question about functions - GameCreators Forum

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Yodaman Jer

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Posted: 18th Oct 2008 19:46

Sorry for the noobish question, everybody. I've been programming for a year and I still don't quite know how functions...function.

I have a couple of questions. First, does using functions actually keep your game running fast?

Second, how do you call them? I think I read somewhere that you use gosub, but I'm not certain.

Again, I apologize for noobish-ness. I can't believe I waited this long to ask about functions.

Yodaman Jer

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Sinani201

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Posted: 18th Oct 2008 20:33

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I don't know if functions make your games go faster, but they do make them much more organized. Here's how they work:

Lets say you make a function called "make_box" Here's how you do that:

+ Code Snippet

function make_box

Now, lets say you want it to take certain perimeters, so that the box can be different depending on how you call it. For a box, our perimeters would be l,r,t,b. Here's how you'd do that:

+ Code Snippet

function make_box(l,r,t,b)

Now, you have to put stuff in the function. Since the function will make a box, we'll tell it to use the BOX command:

+ Code Snippet

function make_box(l,r,t,b)
box l,r,t,b
endfunction

Now, look at the code. Our BOX command takes the perimeters l,r,t,b, and those are also the perimeters of the function. I also ended the function with ENDFUNCTION, which, ends the function. Now, we have to call the function:

+ Code Snippet

make_box(5,7,8,4)

function make_box(l,r,t,b)
box l,r,t,b
endfunction

Now, it is called. Notice how I put in the numbers as perimeters. Those numbers correspond with the perimeters you put when making the function; hence l=5, r=7, r=8, and b=4. Then, the box command knows what those variables are, so you'd be calling BOX 5,7,8,4.

Those are the basics of functions. Note that you don't have to use numbers for this; you can also use strings and floats, as well.

"I reveal my trap card, GEORGE DUBYA BUSH!
America loses 2000 Life Points! America loses." -Deucalion2

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Yodaman Jer

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Posted: 18th Oct 2008 20:51

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Thanks Sinani! I understand how that works. I'll give it a shot!

Yodaman Jer

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BN2 Productions

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Posted: 19th Oct 2008 01:31

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Here is a couple big things about using functions:

1. Don't go crazy, if you end up having 6+ parameters, you could probably just use a subroutine (using gosub).

2. Variables are only local. That means that variables in your main code won't have any value in the functions that you make unless....

3. Arrays, due to a glitch, are global variables. This means that array(1) in your main code and array(1) in a function are the SAME VARIABLE! This can be used for extra tricks, though it does create problems if you use #include.

4. The variables in the function maintain their value even after the function is finished. This means that if you have a flag variable, make sure to reset it at the beginning or end of the function, otherwise when you call it again, it will still have the same value as it did at the end of the functions last calling.

Ever notice how in Microsoft word, the word "microsoft" is auto corrected to be "Microsoft" but "macintosh" just gets the dumb red underline?

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Sixty Squares

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Posted: 19th Oct 2008 16:54 Edited at: 19th Oct 2008 16:58

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Quote: "4. The variables in the function maintain their value even after the function is finished. This means that if you have a flag variable, make sure to reset it at the beginning or end of the function, otherwise when you call it again, it will still have the same value as it did at the end of the functions last calling."

I beg to differ:

+ Code Snippet


do
cls
set cursor 0,0
IncNum()
loop

End
Function IncNum()
inc g,1
print "variable g: ",g
Endfunction

If what you said is true, then shouldn't the variable "g" keep increasing?

EDIT: Oh wait I'm using DBP it may be different in DBC.

EDIT 2: Odd, I just tested the code and the variable does keep increasing in DBC. They changed the way functions worked when they made DBP. I did not know that. Ignore this post

Snow Demo

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BN2 Productions

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Posted: 19th Oct 2008 18:53

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I think it is a bug, similar to the array bug. It seems too inconvenient to be expected.

Ever notice how in Microsoft word, the word "microsoft" is auto corrected to be "Microsoft" but "macintosh" just gets the dumb red underline?

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Latch

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Posted: 19th Oct 2008 19:16

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The array thing isn't a bug. It's stated specifically in the help that you declare it global outside of a function and you declare it local inside of a function. A local array cannot be accessed outside of a function.

The variables inside of a function being static may or may not be a bug. In other programming languages, you can set a variable inside of a function to be static. The advantage of this may be to have the variable inside the function behave much like a global variable but be influenced and accessible only by the function. This is a lame example but:

+ Code Snippet

sync on

make matrix 1,5000,5000,25,25
make object cube 1,25
do
   accelerate(1)
   turn object right 1,(rightkey()-leftkey())*4
   position camera object position x(1),30,object position z(1)-100
   sync
loop


end

function accelerate(obj)
   inc speed
   move object obj,speed
   if speed > 100 then speed=1
endfunction

You could create a function that performs an oscillation or something.

Enjoy your day.

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Ed222

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Posted: 19th Oct 2008 20:14

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Quote: "Oh wait I'm using DBP it may be different in DBC"

Yes it is different. You can use the same variable in functions and elsewhere else in the game with out declaring it as global and still have the same value.

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Yodaman Jer

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Posted: 19th Oct 2008 20:15 Edited at: 19th Oct 2008 20:35

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Thanks everyone! I'm going to try out functions, now that I'm not scared of them...

Errmmm....I tried running it, and it displayed an error message.
It said 'Runtime error at line 16: Program ran into a function declaration.'

Here's my code:

+ Code Snippet

`%%%%%%%%%%%%%%%%
`SET UP THE PROGRAM
`%%%%%%%%%%%%%%%%
Set display mode 800,600,32
sync on : sync rate 40
backdrop on : autocam off

make_box(5,7,6,8)




`%%%%%%%%%%%%%%%
`FUNCTIONS
`%%%%%%%%%%%%%%%
function make_box(l,r,t,b)
box l,r,t,b
endfunction

Anything look wrong?

Yodaman Jer

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TheComet

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Posted: 19th Oct 2008 20:31

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Any variables inside a function don`t interact with the code outside of the function, and variables outside a function don`t interact with the code inside a function.

Here, g will be 1 outside the function, but inside it will be 0.

+ Code Snippet

rem setup screen
sync on
sync rate 0
backdrop on

rem set a variable
g=1

rem main loop
do

rem print g
text 0,0,"value of g outside the function : "+str$(g)

rem call the function
print_g()

rem refresh screen
sync

rem end of main loop
loop

rem function --------------------
function print_g()

text 0,30,"value of g in the function : "+str$(g)

endfunction

Now, if I put "g=1" in the function, g outside the function will be 0, but inside the function it will be 1:

+ Code Snippet

rem setup screen
sync on
sync rate 0
backdrop on

rem main loop
do

rem print g
text 0,0,"value of g outside the function : "+str$(g)

rem call the function
print_g()

rem refresh screen
sync

rem end of main loop
loop

rem function --------------------
function print_g()

rem set a variable
g=1

text 0,30,"value of g in the function : "+str$(g)

endfunction

Now, if I pass information into the function, both will be 1:

+ Code Snippet

rem setup screen
sync on
sync rate 0
backdrop on

rem set a variable
g=1

rem main loop
do

rem print g
text 0,0,"value of g outside the function : "+str$(g)

rem call the function
print_g(g)

rem refresh screen
sync

rem end of main loop
loop

rem function --------------------
function print_g(g)

text 0,30,"value of g in the function : "+str$(g)

endfunction

And if you wan`t info to leave the function outside the function, add the variable at the end of "endfunction":

+ Code Snippet

rem call function
g=print_g()

rem end of the function
endfunction g

Then it will look like this:

+ Code Snippet

rem setup screen
sync on
sync rate 0
backdrop on

rem main loop
do

rem print g
text 0,0,"value of g outside the function : "+str$(g)

rem call the function
g=print_g()

rem refresh screen
sync

rem end of main loop
loop

rem function --------------------
function print_g(g)

g=1
text 0,30,"value of g in the function : "+str$(g)

endfunction g

Hope that helps!

TheComet

Suicide is away of telling God, You can’t fire me I quit !!!!!

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Latch

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Posted: 19th Oct 2008 20:58

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Quote: "Errmmm....I tried running it, and it displayed an error message.
It said 'Runtime error at line 16: Program ran into a function declaration.'"

As a general rule with DBC, create all of your functions at the end of the code. And before the first declaration, use END

+ Code Snippet

main program
blah
blah

do
   inc g
   hi#=g+1
   myfunction(g hi#)
   thisorthat()
loop

END

function myfunction(g,hi#)
   blah
endfunction

function thisorthat()
   blah blah
endfunction

etc.

Enjoy your day.

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Sixty Squares

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Posted: 19th Oct 2008 20:59 Edited at: 19th Oct 2008 20:59

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Quote: "Errmmm....I tried running it, and it displayed an error message.
It said 'Runtime error at line 16: Program ran into a function declaration.'"

There is nothing wrong with your code. However, it runs the "Make_Box" function, then keeps going. The compiler can't actually run the Function command, which declares the function. It can only run function calls. So, just declare all of your functions at the end (like you have) and write END before them. This way the program ends before it can get to the functions and give you that error.

EDIT: It seems Latch just beat me to it

Snow Demo

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Yodaman Jer

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Posted: 19th Oct 2008 21:03

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Yes yes, that seems to have solved the problem.

Thanks latch and Sixty Squares!

Yodaman Jer

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Libervurto

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Posted: 20th Oct 2008 01:36

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@Yodaman
You're not alone, it took me aaages to finally understand how to use functions properly.
I had a bit of a break-through recently when I realised I could make a function that used a "lower-level" function, this helped make everything a lot simpler.
Here's an example of this tiered function idea.

+ Code Snippet

`------------
` Functions
`------------
`---Tier 3---
Function IsoCube(x,y,z,size)
   `get vertex co-ords
   ax= x-size : bx= x+size
   ay= y-size : by= y+size
   az= z-size : bz= z+size

   rem base
   IsoLine(ax,ay,az,ax,ay,bz)
   IsoLine(bx,ay,az,ax,ay,az)
   rem left side
   IsoLine(ax,ay,bz,ax,by,bz)
   rem right side
   IsoLine(bx,ay,az,bx,by,az)
   rem centre side
   IsoLine(ax,ay,az,ax,by,az)
   rem top face
   IsoLine(ax,by,bz,bx,by,bz)
   IsoLine(bx,by,bz,bx,by,az)
   IsoLine(ax,by,az,ax,by,bz)
   IsoLine(bx,by,az,ax,by,az)
Endfunction

`---Tier 2---
rem Isometric Line
Function IsoLine(ax,ay,az,bx,by,bz)
  cx= IsoX(ax,ay,az)
  cy= IsoY(ax,ay,az)
  dx= IsoX(bx,by,bz)
  dy= IsoY(bx,by,bz)
  line cx,cy,dx,dy
Endfunction

`---Tier 1---
rem Isometric X
Function IsoX(x,y,z)
  sx = w(0)+ (x+x)/3. - (z+z)/3.
Endfunction sx

rem Isometric Y
Function IsoY(x,y,z)
  sy = h(0)- (x/3. + z/3. + (y+y)/3.)
Endfunction sy

Writing the functions in tiers gives me more flexibility. If I decided I wanted to write some text at an isometric position I could use the lower-tier IsoX/Y/Z functions; if I'd written the IsoLine or IsoCube functions containing the formulas for the IsoX/Y/Z conversion I wouldn't have access to the formulas independently.

Here's a program I used them in.

rem setup
Dim w(0)
Dim h(0)
w(0)= 512
h(0)= 384
Set Display Mode w(0)*2,h(0)*2,32
h(0)= 512 : rem reposition vertical centre for drawing purposes
hide mouse
set text font "tahoma",1
set text size 18
sync on : sync rate 40

rem Define some colours
white = rgb(255,255,255)
grey  = rgb(127,127,127)
red   = 255*65536
green = 255*256
blue  = 255

rem --Axis Lines--
ink white,0
text 0,0,"Here are the 3D axis as they are represented in isometric 2D."

rem X axis
ink red,0
IsoLine(0,0,0,400,0,0)
center text IsoX(420,10,0),IsoY(420,10,0),"X"
rem Y axis
ink green,0
IsoLine(0,0,0,0,400,0)
center text IsoX(0,440,0),IsoY(0,440,0),"Y"
rem Z axis
ink blue,0
IsoLine(0,0,0,0,0,400)
center text IsoX(0,10,420),IsoY(0,10,420),"Z"

sync
wait key
cls 0

rem --Ground Level X/Z Grid--
ink white,0
text 0,0,"This is an X/Z grid positioned at 0 on the Y axis."

For n= 0 to 400 step 40
  rem X axis
  ink red,0
  IsoLine(0,0,n,400,0,n)
  rem Z axis
  ink blue,0
  IsoLine(n,0,0,n,0,400)
Next n

sync
wait key

rem --First Floor X/Z Grid--
rem animate extruding second floor
For y= 0 to 110
  cls
  ink white,0
  text 0,0,"A second floor is extruded to show how 3D height affects 2D position."

For n= 0 to 400 step 40
    rem -Ground-
    ink white,0
    rem X axis
    IsoLine(0,0,n,400,0,n)
    rem Z axis
    IsoLine(n,0,0,n,0,400)

rem -Floor 1-
    ink green,0
    rem X axis
    IsoLine(0,y,n,400,y,n)
    rem Z axis
    IsoLine(n,y,0,n,y,400)
  Next n

sync
Next y

wait key
cls

rem --Join by Y axis--
ink white,0
text 0,0,"The two floors are joined to make an array of cuboids."

For n= 0 to 400 step 40
  ink white,0
  rem -Ground-
  rem X axis
  IsoLine(0,0,n,400,0,n)
  rem Z axis
  IsoLine(n,0,0,n,0,400)

rem -Floor 1-
  rem X axis
  IsoLine(0,110,n,400,110,n)
  rem Z axis
  IsoLine(n,110,0,n,110,400)

rem -Joiners-
  ink green,0
  for z= 0 to 400 step 20
    IsoLine(n,0,z,n,110,z)
  next z
Next n

sync
wait key
cls

rem --3D Shapes--
ink white,0
text 0,0,"Isometric coordinates can be used to represent 3D objects with relative ease."

rem -Cube-
ink red,0
IsoCube(-75,25,25,25)

rem -Pyramid-
ink green,0
rem base
IsoLine(0,0,0,0,0,50)
IsoLine(50,0,0,0,0,0)
rem left side
IsoLine(0,0,50,25,50,25)
rem right side
IsoLine(50,0,0,25,50,25)
rem centre line
IsoLine(0,0,0,25,50,25)

sync
wait key
cls

END

`------------
` Functions
`------------
`---Tier 3---
Function IsoCube(x,y,z,size)
   `get vertex co-ords
   ax= x-size : bx= x+size
   ay= y-size : by= y+size
   az= z-size : bz= z+size

rem base
   IsoLine(ax,ay,az,ax,ay,bz)
   IsoLine(bx,ay,az,ax,ay,az)
   rem left side
   IsoLine(ax,ay,bz,ax,by,bz)
   rem right side
   IsoLine(bx,ay,az,bx,by,az)
   rem centre side
   IsoLine(ax,ay,az,ax,by,az)
   rem top face
   IsoLine(ax,by,bz,bx,by,bz)
   IsoLine(bx,by,bz,bx,by,az)
   IsoLine(ax,by,az,ax,by,bz)
   IsoLine(bx,by,az,ax,by,az)
Endfunction

`---Tier 2---
rem Isometric Line
Function IsoLine(ax,ay,az,bx,by,bz)
  cx= IsoX(ax,ay,az)
  cy= IsoY(ax,ay,az)
  dx= IsoX(bx,by,bz)
  dy= IsoY(bx,by,bz)
  line cx,cy,dx,dy
Endfunction

`---Tier 1---
rem Isometric X
Function IsoX(x,y,z)
  sx = w(0)+ (x+x)/3. - (z+z)/3.
Endfunction sx

rem Isometric Y
Function IsoY(x,y,z)
  sy = h(0)- (x/3. + z/3. + (y+y)/3.)
Endfunction sy

+ Code Snippet

rem setup
Dim w(0)
Dim h(0)
w(0)= 512
h(0)= 384
Set Display Mode w(0)*2,h(0)*2,32
h(0)= 512 : rem reposition vertical centre for drawing purposes
hide mouse
set text font "tahoma",1
set text size 18
sync on : sync rate 40

rem Define some colours
white = rgb(255,255,255)
grey  = rgb(127,127,127)
red   = 255*65536
green = 255*256
blue  = 255

rem --Axis Lines--
ink white,0
text 0,0,"Here are the 3D axis as they are represented in isometric 2D."

rem X axis
ink red,0
IsoLine(0,0,0,400,0,0)
center text IsoX(420,10,0),IsoY(420,10,0),"X"
rem Y axis
ink green,0
IsoLine(0,0,0,0,400,0)
center text IsoX(0,440,0),IsoY(0,440,0),"Y"
rem Z axis
ink blue,0
IsoLine(0,0,0,0,0,400)
center text IsoX(0,10,420),IsoY(0,10,420),"Z"

sync
wait key
cls 0

rem --Ground Level X/Z Grid--
ink white,0
text 0,0,"This is an X/Z grid positioned at 0 on the Y axis."

For n= 0 to 400 step 40
  rem X axis
  ink red,0
  IsoLine(0,0,n,400,0,n)
  rem Z axis
  ink blue,0
  IsoLine(n,0,0,n,0,400)
Next n

sync
wait key

rem --First Floor X/Z Grid--
rem animate extruding second floor
For y= 0 to 110
  cls
  ink white,0
  text 0,0,"A second floor is extruded to show how 3D height affects 2D position."

  For n= 0 to 400 step 40
    rem -Ground-
    ink white,0
    rem X axis
    IsoLine(0,0,n,400,0,n)
    rem Z axis
    IsoLine(n,0,0,n,0,400)

    rem -Floor 1-
    ink green,0
    rem X axis
    IsoLine(0,y,n,400,y,n)
    rem Z axis
    IsoLine(n,y,0,n,y,400)
  Next n

  sync
Next y

wait key
cls

rem --Join by Y axis--
ink white,0
text 0,0,"The two floors are joined to make an array of cuboids."

For n= 0 to 400 step 40
  ink white,0
  rem -Ground-
  rem X axis
  IsoLine(0,0,n,400,0,n)
  rem Z axis
  IsoLine(n,0,0,n,0,400)

  rem -Floor 1-
  rem X axis
  IsoLine(0,110,n,400,110,n)
  rem Z axis
  IsoLine(n,110,0,n,110,400)

  rem -Joiners-
  ink green,0
  for z= 0 to 400 step 20
    IsoLine(n,0,z,n,110,z)
  next z
Next n

sync
wait key
cls

rem --3D Shapes--
ink white,0
text 0,0,"Isometric coordinates can be used to represent 3D objects with relative ease."

rem -Cube-
ink red,0
IsoCube(-75,25,25,25)


rem -Pyramid-
ink green,0
rem base
IsoLine(0,0,0,0,0,50)
IsoLine(50,0,0,0,0,0)
rem left side
IsoLine(0,0,50,25,50,25)
rem right side
IsoLine(50,0,0,25,50,25)
rem centre line
IsoLine(0,0,0,25,50,25)

sync
wait key
cls

END

`------------
` Functions
`------------
`---Tier 3---
Function IsoCube(x,y,z,size)
   `get vertex co-ords
   ax= x-size : bx= x+size
   ay= y-size : by= y+size
   az= z-size : bz= z+size

   rem base
   IsoLine(ax,ay,az,ax,ay,bz)
   IsoLine(bx,ay,az,ax,ay,az)
   rem left side
   IsoLine(ax,ay,bz,ax,by,bz)
   rem right side
   IsoLine(bx,ay,az,bx,by,az)
   rem centre side
   IsoLine(ax,ay,az,ax,by,az)
   rem top face
   IsoLine(ax,by,bz,bx,by,bz)
   IsoLine(bx,by,bz,bx,by,az)
   IsoLine(ax,by,az,ax,by,bz)
   IsoLine(bx,by,az,ax,by,az)
Endfunction

`---Tier 2---
rem Isometric Line
Function IsoLine(ax,ay,az,bx,by,bz)
  cx= IsoX(ax,ay,az)
  cy= IsoY(ax,ay,az)
  dx= IsoX(bx,by,bz)
  dy= IsoY(bx,by,bz)
  line cx,cy,dx,dy
Endfunction

`---Tier 1---
rem Isometric X
Function IsoX(x,y,z)
  sx = w(0)+ (x+x)/3. - (z+z)/3.
Endfunction sx

rem Isometric Y
Function IsoY(x,y,z)
  sy = h(0)- (x/3. + z/3. + (y+y)/3.)
Endfunction sy

@All
Does this method slow down the computer?

A small program that works is better than a large one that doesn't.

DBC Challenge Rank: Rookie

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Ed222

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Posted: 20th Oct 2008 02:14

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Quote: "Here, g will be 1 outside the function, but inside it will be 0"

woops guess I was wrong but it does work if you declear is as global

+ Code Snippet

rem setup screen
sync on
sync rate 0
backdrop on

rem set a variable
global g=1

rem main loop
do

rem print g
text 0,0,"value of g outside the function : "+str$(g)

rem call the function
print_g()

rem refresh screen
sync

rem end of main loop
loop

rem function --------------------
function print_g()

text 0,30,"value of g in the function : "+str$(g)

endfunction

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TheComet

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Posted: 20th Oct 2008 20:55

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DBC doesn`t have the command "Global"...

But yes, that`s true.

Suicide is away of telling God, You can’t fire me I quit !!!!!

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Yodaman Jer

User Banned

Posted: 20th Oct 2008 21:17

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Thanks everyone! Great help here! I now understand the basic use of a function.

Yodaman Jer

Guitarist, 3D modeler, Video editor, Renaissance Faire performer, Christian, and all-around GEEK. With a capital 'G'.

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Latch

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Posted: 22nd Oct 2008 18:10

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Also make sure you check out TDK's tutorials:

Functions

Enjoy your day.

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DarkBASIC Discussion / Question about functions