revJournal - Features

Making of ArcadeEngine

Once I started with Revolution I was looking for a more affordable alternative to Macromedias Director. I just had finished Multimedia Highschool and had my diploma as Mediengestalter Bild und Ton (Mediadesigner for Video and Audio) from Hamburgs Chamber of Commerce in my pocket. Setting up my one man company I wanted to create Multimedia CD-Roms as advertising medium and thought I needed an authoring system that allowed me to build nice menus around my movies.

Looking on versiontracker for an alternative to Director I discovered the Revolution 1.1.1 Starter Kit and became hooked. With the help of the use-list I managed to solve the problems I had on my learning curve. I was in touch with one of the biggest german Macintosh magazines at that time and they asked me to write a review and workshop on using Revolution and that´s how the story started.

I thought that I should test more of Revs multimedia abilities, as I needed to compare features directly to other autjoring systems, emphasis on the comparison with Director. So I created a few simple animations. Soon I discovered that the animation manager that came with Revolution by that time had its weaknesses. So I tried scripting my animations and came up with the first versions of circular movement. I experimented a lot and soon I found it was a good idea to poduce reusable code.

The first version worked pretty well for moving things but was too clumsy to be used by other people than me. I produced a game for a recycling company using the library and it worked well. But it was not convenient enough to share it with other developers. All functions required numerical input to produce meaningful results. I used to explicitly pass parameters to the functions I used, so if I wanted to do something with two controls locations, I needed to split those locations into their x and y coordinates in the calling script. A calling script snipped looked like this:

   put item 1 of the loc of btn "myButton1" into x1
   put item 2 of the loc of btn "myButton1" into y1
   put item 1 of the loc of btn "myButton2" into x2
   put item 2 of the loc of btn "myButton2" into y2
   get distance(x1,y1,x2,y2)

The distance function looked like this:

   function distance x1,y1,x2,y2
     put x1-x2 into oppositeLeg
     put y1-y2 into adjacentLeg
     put round(sqrt (oppositeLeg^2+adjacentLeg^2)) into hypotenuse
     return hypotenuse
   end distance

This worked, but required a lot of scripting in the stack. What I wanted to be able to do was a single function call like this:

   get distance(the loc of btn "myButton1",the loc of btn "myButton2")

So I needed to revise all the functions I had. That meant a few more lines of script in the library, but ease of use when working with it. The same function, including error checking for the parameters now looks like this:

   function distance
      repeat with i=1 to paramcount()
        if i<paramcount() then
          put param(i)&"," after theValue
        else
          put param(i) after theValue
        end if
      end repeat
      repeat with i=1 to the number of items of theValue
        if item i of theValue is not a number then
          return "Error: All Parameters must be numbers!"
          exit distance
          exit repeat
        end if
      end repeat
      put item 1 of theValue into x1
      put item 2 of theValue into y1
      put item 3 of theValue into x2
      put item 4 of theValue into y2
      if y2 is empty then
        return "Error: Syntax is distance(x1,y1,x2,y2)"&cr&theValue
      end if
      put x1-x2 into oppositeLeg
      put y1-y2 into adjacentLeg
      put round(sqrt (oppositeLeg^2+adjacentLeg^2)) into hypotenuse
      return hypotenuse
   end distance

Now the function allowed both numerical and easy input which is eactly what I wanted it to.

My little library now had some functions and handlers to move controls and also the first basic collision detection routine. I produced another game for the recycling company which was well received. I was asked to talk on the EuroRevCon on Malta. So I put together a few simple demo stacks and met many nice people there. I had the chance to talk to Kevin Miller about the things I do with Revolution and we discussed the furture of my library in a later meeting in Edinburgh.

It soon became clear that it had the potential to help others creating games and animations. But still there were a few things missing. I added pixel precise collision detection for images, some nice path creation routines and a few more geometric functions.

I concentrated on optimizing existing handlers and functions for speed. My goal was to make everything run smoothly on my oldest machine, a G4-400 MHz. And it needed to be as stable as possible.

There were quite a few people helping me a lot throughout development with constructive critisism, suggestions and kicks in the butt when I needed them. The 1.0 version was very well received. After taking a few days off I looked at the documentation again and thought: "Hey, it is a multimedia library, but it looks horrible!" So I invested a few days in a new documentation system and added a few functions for point in polygon tests and polygon polygon collisions.

If you want to see the library in action you can download a demo app here:

Windows:
http://www.runrev.com/section/revselect/arcadeengine/downloads/aedemo_win.zip

Mac Os X:
http://www.runrev.com/section/revselect/arcadeengine/downloads/aedemo_x.dmg

Linux:
http://www.runrev.com/section/revselect/arcadeengine/downloads/aedemo_linux.zip

Rev Library
If you want to play with the library you can download the trial version here:
http://www.runrev.com/section/revselect/arcadeengine/downloads/Arcade_Engine_1.5_Trial.zip