Bob does not exist?? - GameCreators Forum

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palex3

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Joined: 15th Dec 2004

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Posted: 18th Jan 2005 09:36

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I'm doing a space invaders-type game... Whenever I check for collision, I get a "Bob does not exist" message and the program ends...I just have one ship and one alien for now... Source code included...

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pizzaman

21

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Joined: 18th Feb 2004

Location: Gateshead, UK

Posted: 18th Jan 2005 10:32

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The problem is your checking for a sprite collision between sprites 2 and 3, yet sprite 2 is not created until you press the space bar, thats why you get the error.

Your code should be (note I've cleaned it up a bit)

+ Code Snippet

sync on
load bitmap "ship.bmp",1

Get image 1,0,0,24,24

load bitmap "bullet.bmp",1

get image 2,0,0,24,24

load bitmap "alien.bmp",1

get image 3,0,0,24,24




pos#=240
bullet#=351

hide mouse


do

   Sprite 1,pos#,375,1 
   sprite 3,pos#,24,3

   if rightkey()=1
      pos#=pos#+10
   endif

   if leftkey()=1
      pos#=pos#-10
   endif

   if spacekey()=1 
      bullet#=351

      repeat
	 sprite 2,pos#,bullet#,2
	 bullet#=bullet#-10
         sync
      until bullet#<-30

   endif


   if sprite exist(2) = 1
      if sprite collision(2,3)>0 then hide sprite 3
   endif

   sync

loop

or instead of checking if the sprite exists you could create it before hand like so

+ Code Snippet

sync on
load bitmap "ship.bmp",1

Get image 1,0,0,24,24

load bitmap "bullet.bmp",1

get image 2,0,0,24,24

load bitmap "alien.bmp",1

get image 3,0,0,24,24


sprite 2,pos#,bullet#,2
hide sprite 2

pos#=240
bullet#=351

hide mouse


do

   Sprite 1,pos#,375,1 
   sprite 3,pos#,24,3

   if rightkey()=1
      pos#=pos#+10
   endif

   if leftkey()=1
      pos#=pos#-10
   endif

   if spacekey()=1 
      bullet#=351
      show sprite 2

      repeat
	 sprite 2,pos#,bullet#,2
	 bullet#=bullet#-10
         sync
      until bullet#<-30

   endif

   if sprite collision(2,3)>0 then hide sprite 3

   sync

loop

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palex3

20

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Joined: 15th Dec 2004

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Posted: 18th Jan 2005 23:30

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thanks, I don't get the error message, but the bullet still goes right through...

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The Game Programmer

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Joined: 4th Dec 2004

Location: Sitting, and waiting, and staring, and..

Posted: 19th Jan 2005 03:40

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Hi, I'm also making a space shooter thing. I'm basing mine off the tutorial stickied in the 2d section, you're answer might be in the code there, take a look, and if you have any questions just email or IM me and I'll try to help. I'm probably having the same basic problems that you are. I posted in the newcomers forum if you want to look, including all my code and media.

Well, I'm trying aren't I.....

When Life gives you lemons make orange juice. Then sit back and wonder how it was done.

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pizzaman

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Joined: 18th Feb 2004

Location: Gateshead, UK

Posted: 19th Jan 2005 09:02

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The problem is when you fire the bullet it goes into its own loop, which sends the bullet across the screen, but you not checking for any collision.

Try this, examine it closely, and make sure you know what each part does, before you continue to work on this.

+ Code Snippet

sync on
load bitmap "ship.bmp",1

Get image 1,0,0,24,24

load bitmap "bullet.bmp",1

get image 2,0,0,24,24

load bitmap "alien.bmp",1

get image 3,0,0,24,24




pos#=240
bullet#=351

hide mouse


do

   Sprite 1,pos#,375,1
   sprite 3,pos#,24,3

   if rightkey()=1
      pos#=pos#+10
   endif

   if leftkey()=1
      pos#=pos#-10
   endif

   if spacekey()=1 and BulletFired = 0
      bullet#=351
      BulletFired = 1
   endif

   if BulletFired = 1
      sprite 2,pos#,bullet#,2
      bullet#=bullet#-10
      if bullet# < -30 then BulletFired = 0
   endif

   if sprite exist(2) = 1
      if sprite collision(2,3)>0 then hide sprite 3
   endif

   sync

loop

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palex3

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Joined: 15th Dec 2004

Location:

Posted: 20th Jan 2005 03:20

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ok, I got it this time...thaks a lot, that cleared up a lot of stuff!

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2D All the way! / Bob does not exist??