Archive for the ‘Bold Pixel Engine’ tag

Performance vs Error Checking

Hi everyone, Vlad here!

Seems like on a thing versus some other thing rampage with Application Design vs Game Design shortly followed by this post. I guess that’s a good thing, it means there are challenges and doubts and that we need to research.

This post is also inspired by some books I’ve been reading lately and that I highly recommend: The Productive Programmer that was influenced by The Pragmatic Programmer.

Problem #1

We are writing code and there’s not such thing as writing code without bugs. Sometimes our oldest, most used code, that code that we trust each of our games with gets into a specific spot where a hidden bug appears and we spend hours and hours figuring out what’s happening.

Solution #1 is Problem #2

There are several solutions to this. Writing code that includes testing is in my opinion the best. The problem with this, game development wise and specifically in scripted languages such as AS3, is that this makes the code much slower. The solution was checking for inconsistencies and not performing operations instead of throwing errors and exceptions.

I ended up creating conditions for use. For instance our blit package uses three different types: the core, the object and the texture. The core keeps the state of the whole system, the object keeps the state of what and where to render and the texture keeps the state of BitmapData. If the object did not have a texture it would simply not render. Sounds pretty cool, right?

To be honest… wrong…

Problem #2.1

First problem was the times where the position had NaN value instead of a Number. This rarely happened but every time it did it was a huge headache to identify why and then track the source of the bug down. While this seems unrelated, the fact was the it looked like the texture did not exist. So I had to check if the texture was created, if it was passed, if it was there at all and the worst part was that if the texture was there as it should, where the hell was the problem?

Problem #2.2

Performance wise checking if there is a texture is absolutely dumb! 99% of the times there is a texture present. More, the object class has a visible variable. If the object does not have a texture why is it visible in the first place?

So while apparently I solved a problem by checking if the texture was present and not performing any blit operation if it wasn’t, the truth is that both performance wise (not that serious by the way, it’s just a if statement) and the unwanted problems it induced in the code backfired from time to time.

I spread this type of behavior through the code. While one if statement does not have a large impact in performance, a lot of checking piles up and I had a lot!

Solution #2

A short story and a riddle both taken from those books that explain my thoughts on the ‘final’ (we’ll see about that!) solution for these problems.

The first one was when one of the authors was hired as a consultant for a development project where the coders sent broken code to the version control system. What he did was to create a routine where the version control server would compile the code that was pushed. Every time the compilation didn’t work the server would send an email with the error. With the amount of mail with errors constantly piling up on mailboxes, one of the coders asked if there was a way of not getting that much email. The consultant replied: “Sure, don’t push code with errors!”

The riddle is… what code takes not time to be executed? The one that is not compiled.

So the solution is to write code that allows zero error tolerance while not compiling it. The way to achieve this is with conditional compilation which can be used in several way but these are the ones I believe the most useful is to use code blocks, like this:

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private function someFunction():void {
    CONFIG::debug {
        // Development code
    }
    CONFIG::release {
        // Final code
    }
    // Both dev and final code
}

Inside the same function, different code is compiled depending on the current configuration. We can have several checks with exceptions and errors being thrown and then have a ‘don’t check at all’ version in the release configuration.

This is a two stage solution really. On one hand every time I do something stupid, I get errors so my code has to be perfectly implemented at least when it comes to our framework. On the other hand the same code that make me code as best as I can is also the code that does not run in the final version.

 

Posted: February 5th, 2012
at 12:55am by Vlad

Tagged with , , , , ,


Categories: Dev Journal: Danger Zone,The code of VGS

Comments: 4 comments


Enhancing by refactoring

Two years ago I read a lot about OOP. Every time I picked a new concept in some forum or chat I’d do my best to understand and apply it. I was eager to improve my coding knowledge and skills but everything we code as a purpose and an audience and if we forget the purpose or the audience we are introducing more problems with the knowledge we have than solving problems.

That happened with Bold Pixel. At some point in time Bold Pixel became a monster to please developers instead of a tool to be more productive in my purpose to my audience: create games for players! People play games, not code!

I stopped over-engineering sometime ago and started reading about how to become a better programmer not by writing better code, but by writing the exact code to solve the exact problem. This brought a new problem: what to do with Bold Pixel and how to maintain and evolve it? First thing was to start a new package and only bring in classes that I needed but wire the classes up to be as slim and straight to the point as possible. I do that all the time to build up my code base right now, but that’s not all. Here’s the whole process I’m using right now.

Start simple

 

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class BlitObject {
    // Position
    public var x:Number = 0;
    public var y:Number = 0;
    // Rendering
    public var visible:Boolean = true;
    public function BlitObject():void {
        // Constructor
    }
    internal function render():void {
        // Render stuff here
    }
}

The class above can be a stub for a simple blit object. From a OOP perspective it breaks encapsulation completely since x, y and visible variables should be private but seriously, do I really need those to be private or protected and have getters and setters? No I don’t so no need to over-engineer it. The only thing I want to have contained is the render method that should only be called by the blit engine that lives in the same package.

The blit object only responsibility is to copyPixels or draw on a given world position translating camera position on the fly.

Writing a simple class like this is fast, performs fast, case closed.

Evaluate new needs

Now I need a tile map class. This class is also a blit object so following the “is a” versus “has a” rule tile map should inherit blit object. Considering the blit engine has a camera, the tile map won’t move. This brings two new problem.

1. If the tile map doesn’t move, why do I have x and y publicly accessible?
2. I want my camera to follow blit objects so blit objects must have x and y variables (or properties). How can I make tile map be recognized as a blit object, have x and y and have none of those altered?

Sounds messy…

I could write a Blittable interface that would define a render function and getter and setter methods for x and y. The problem is that if there’s something I want to keep in the package scope is the render function and interfaces define public interfaces.

The solution is to convert blit object in an abstract class and have its original functionality moved to a new graphic class.

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class BlitObject {
    // Rendering
    public var visible:Boolean = true;
    internal function render():void {
        throw new Error("Abstract function called. Override render()!");
    }
    public function get x():Number {
        return NaN;
    }
    public function set x(v:Number):void {
        throw new Error("Abstract function called or property x not available.");
    }
    public function get y():Number {
        return NaN;
    }
    public function set y(v:Number):void {
        throw new Error("Abstract function called or property y not available.");
    }    
}
class Graphic extends BlitObject {
    // Position
    private var _x:Number = 0;
    private var _y:Number = 0;
    override internal function render():void {
        // Render stuff here
    }
    // Position
    override public function get x():Number { return _x }
    override public function set x(v:Number):void { _x = v }
    override public function get y():Number { return _y }
    override public function set y(v:Number):void { _y = v }
}
class TileMap extends BlitObject {
    override internal function render():void {
        // Render the tile map
    }
}

Problem solved. The class responsibilities are much better defined.

1. A blit object renders and has x and y coordinates. Since it is an abstract class everything we try to do with it directly will result in an error.
2. A graphic is a world movable blit object that renders by copyPixel or draw.
3. A tile map is a world static blit object that renders very large objects by copyPixel or draw  based on a predefined xml specification.

Conclusion

What’s the conclusion here? Well for starters by this time I’d have a couple of interfaces and probably a helpers. I’m not saying it is wrong to have interfaces and helpers, actually it is preferable, but it would be coding for the sake of coding instead of coding for the sake of making a game. It took me 10 minutes to do this and while I was at it the BlitObject class also extends a ListObject class that really speed up the iteration, addition and removal of objects from the blit engine.

Still… I did repeat my self and the code has suffered another refactoring since then. I’ll leave that for another post but I wonder if you know what’s repeated… :)

Posted: January 28th, 2012
at 2:00am by Vlad

Tagged with , , , , ,


Categories: Dev Journal: Danger Zone,The code of VGS

Comments: No comments


BADJ Day 19: So much stuff…

Nineteen days have gone… WOW! After getting full speed ahead for a number of days, I had a stop for a day… domestic stuff kicked in. A lot of work was finished in those quick days though.

With all physics and blit done, I went straight ahead into coding the level. First task was to look at what I had done previously and finding out… it would be easier to just start over, which I did! One very cool thing is that a Finite State Machine class I wrote earlier really proved its worth and is the base for all stuff in the level. I really have to go through how the level code is structured as soon as the dust settles down since right now a lot can change and it will probably make no sense.

One thing I had to change was the Manager class. Remember I mentioned a dependency to a specific class that put all in motion. That is easier to manage now.

But the really cool thing I did today was to quickly test a console class! I used Junkbyte’s Console 2.4 and I just love it! With it we will be able to change a lot of aspects in the game without recompiling.

What is happening right now? Visually? Not much, there’s a circle representing Bruce on screen. Code wise there’s a lot of stuff going on. For starters all the level classes (controller, factory, scene, blit, physics, etc) are created and doing their thing, so it’s just a matter of adding features to it. The state management system is just beautiful and it will save tons of work!

What is missing? Graphics and stuff getting kicked!

Posted: October 19th, 2010
at 12:29am by Vlad

Tagged with , , ,


Categories: Dev Journal: Bruce Ali

Comments: 1 comment


BADJ Day 12: Quick Update

Today was FANTASTIC! A super productive rainy Thursday brought the rewrite of the blit core. Marco complained he can’t see anything… well… debug and tracing is all I can offer right now since textures and blit entities are not working yet, but at this pace a lot of goodies will appear soon.

To celebrate the sensation of being (finally) at full speed, I’ll prepare a sweet thing tomorrow that I hope will be good for new developers and bring a lot of discussion for more experienced ones. Stay tuned!

Posted: October 7th, 2010
at 11:09pm by Vlad

Tagged with , ,


Categories: Dev Journal: Bruce Ali

Comments: No comments


BADJ Day 11: A successful frustration

So I coded and recoded, tested and retested a Object Pool class with a high degree of success and frustration. I wrote and tested three different pool managers, here’s the story…

Objective: Centralized management of pools

This one was easy. There is a PoolManager that has a static method to get a pool for a certain class. If the pool for that class does not exist, it is created, if it does, it is returned. Objective achieved.

Objective: Lightweight pools

I don’t need pools to be amazingly complex, I just need the pools to get the job done, which is: be faster at getting new objects at the expense of memory. That didn’t go very well. The pools were lightweight alright, but I was not able to make it any faster than creating a objective directly.

This lead to the three versions of the pool manager and still the best performance gain is below 5% for any Bold Pixel entity. I was so frustrated, but then I saw the light!

Not my fault really

After testing and more testing I had a epiphany! What if Bold Pixel’s entities are simply too light to make pooling worth. It would not be something I’d consider. It really never crossed my mind that a instancing a object could be faster than getting it from a linked list kind of pool, but it is and the classes I was dealing with are somewhat heavy considering the inheritance and and composition of several.

The highest gain I got was 8ms in 1000 object. Creating 1000 objects took 54ms and getting 1000 objects from the object pool took 46ms.

The unexpected success

So either my classes are very light or flash behaves rather poorly in managing this. So I tested against some movie clip I had around. Creating 1000 movie clips took 102ms, almost doubling the worst case scenario.

Not only I was happy to note that my classes are lightweight, both pool manager and entity type classes, but I also proved that getting movie clips would make a difference.

Conclusion

I’m not happy with the pool manager for now, but I’ll work on it some other day. It gets the job done, but the objects I really wanted to make a better use of pooling are the ones that problably will have less impact.

If I regret anything in this bits of code is that I over engineered it at first. Tomorrow blit engine!

Posted: October 7th, 2010
at 12:56am by Vlad

Tagged with , , , ,


Categories: Dev Journal: Bruce Ali

Comments: 8 comments


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