LiveCode Forums.

Posted: **Thu Nov 13, 2014 10:17 am**

Hello, so I am currently at a stump. I am creating a simple space shooter for my Advanced Higher project (Scottish qualification), and right now I cannot seem to have enemy aliens spawn in. Could anyone give me pointers on how I would go about this?

Many thanks, Conall

Posted: **Thu Nov 13, 2014 2:59 pm**

Hi there,
Check this http://forums.livecode.com/viewtopic.php?f=22&t=19380
a very nice space shooter done by a forum member.
Do you want to spawn based on "time" or by an action "intersect" ?
If you have some code will be nice if you can post ...
This is a must for you to check, will answer many of your questions ...
https://sites.google.com/a/pgcps.org/livecode/home

Regards!
Catalin

Posted: **Mon Nov 24, 2014 12:30 pm**

Hi Catalin, many thanks for taking the time to reply. Also, apologies for taking so long to get back to you, I've had other school work

.

Fortunately, I do have some code! Here it is:

Code: Select all

on startalien
   
   create img
   put it into myImg
   set the text of myImg to the text of img "canvas.png"
   
   set the loc of image "canvas.png" to (random(500),0)
   
   //Undecied on size yet, Decide on size
   
   set the width of "canvas.png" to 128
   set the height of "canvas.png" to 32
   
   movealien
   
end startalien

function checkalien
   if there is an image "shooter" then
      if the top of image "canvas.png" >= the bottom of image "shooter" and the top of image "canvas.png" <= the top of image "shooter" then
         if the left of image "canvas.png" >= the left of image "shooter" and the right of image "canvas.png" <= the right of image "shooter" then
            return true
         end if
      end if
   end if
end checkalien

on movealien
   
   if the visible of "canvas.png" is false then set the visible of image "canvas.png" to true
   set the top of image "canvas.png" to (the bottom of image"canvas.png" + 2)
   if the top of image "canvas.png" >= 582 then
      delete image"canvas.png"
      put (lives - 1) into lives
   else
      if checkalien() is true then
         delete image "canvas.png"
         --         hide group "enemy" with visual effect dissolve very fast 
         set the loc image "shooter" to (327,289)
         send startalien to me in random(1000) milliseconds
         exit movealien
      end if
   end if
   
   if there is an image "canvas.png" then send movealien to me in 4 milliseconds
   
end movealien

This is what I have so far, there is also this too however it does not work.

Code: Select all

on createalien
   
   set the loc of image "canvas.png" to (random(500),0)
   
   set the width of "canvas.png" to 128
   set the height of "canvas.png" to 32
   
   movealien
end createalien

Any help is appreciated!

Posted: **Mon Nov 24, 2014 1:30 pm**

Hi ConallChloride,

when addressing objects in Livecode you ALWAYS need to add the TYPE of object!

##Correct:
...
set the loc of image "canvas.png" to (random(500),0)
...
## NOT correct:
set the width of "canvas.png" to 128
set the height of "canvas.png" to 32
...
## Correct: (img = abbreviation for image)
set the width of IMG "canvas.png" to 128
set the height of IMG "canvas.png" to 32
...

Some general hints!
Whe using lots of nested IF THEN clauses, see, if you can start the other way round!
I mean do not check for TRUE conditions, but for the opposite first, so we can LEAVE the function/handler immediately in that case!
That will shorten your IFs and make them MUCH more readable.

Example, your finction "checkalien", does what it should, but is hardly readable:

Code: Select all

function checkalien
   if there is an image "shooter" then
      if the top of image "canvas.png" >= the bottom of image "shooter" and the top of image "canvas.png" <= the top of image "shooter" then
         if the left of image "canvas.png" >= the left of image "shooter" and the right of image "canvas.png" <= the right of image "shooter" then
            return true
         end if
      end if
   end if
end checkalien

Here my variation, which does exactly the same but is readable and understandable at ONE glance:

Code: Select all

function checkalien
   if there is NOT an image "shooter" then

     ## I think this should ALSO be returned!
      return false
   end if

   if the top of image "canvas.png" < the bottom of image "shooter" and the top of image "canvas.png" > the top of image "shooter" then
      return false
   end if

   if the left of image "canvas.png" < the left of image "shooter" and the right of image "canvas.png" > the right of image "shooter" then
      return true
   end if
    return false
end checkalien

Best

Klaus

Posted: **Wed Nov 26, 2014 12:59 pm**

Many thanks for replying Klaus, I will have a look at what you've said and see what I can do!

Conall

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