  
Welcome to Ventspace! Most posts here are delayed copies of posts from the real Ventspace.
| Thursday, October 1, 2009 |
  Subtleties of .NET and a SlimDX Crash Bug | 
Posted - 10/1/2009 1:49:25 PM | Let's look at a real, in the trenches SlimDX bug that results from a problematic subtlety in .NET. This one isn't even fixed in trunk yet. Here's our main function of interest:
generic<typename T> where T : value class
Result BaseEffect::SetValue( EffectHandle^ parameter, T value )
{
HRESULT hr;
D3DXHANDLE handle = parameter != nullptr ? parameter->InternalHandle : NULL;
if( T::typeid == bool::typeid )
{
BOOL newValue = Convert::ToInt32( value, CultureInfo::InvariantCulture );
hr = InternalPointer->SetBool( handle, newValue );
}
else if( T::typeid == float::typeid )
{
hr = InternalPointer->SetFloat( handle, static_cast<FLOAT>( value ) );
}
else if( T::typeid == int::typeid )
{
hr = InternalPointer->SetInt( handle, static_cast<INT>( value ) );
}
else if( T::typeid == Matrix::typeid )
{
hr = InternalPointer->SetMatrix( handle, reinterpret_cast<D3DXMATRIX*>( &value ) );
}
else if( T::typeid == Vector4::typeid )
{
hr = InternalPointer->SetVector( handle, reinterpret_cast<D3DXVECTOR4*>( &value ) );
}
else
{
hr = InternalPointer->SetValue( handle, &value, static_cast<DWORD>( sizeof(T) ) );
}
return RECORD_D3D9( hr );
}
This function will crash randomly on good input. Specifically, D3D will return a D3DERR_INVALIDCALL, which then gets translated to an exception. Again, that's on known-good input. The call to the function looks like this:
effect.SetValue<float>("alpha", 0.5f);
When this call is made, an EffectHandle is implicitly constructed that copies the string into native memory. Here's the relevant bits of EffectHandle:
EffectHandle::EffectHandle( String^ name )
{
m_StringData = Marshal::StringToHGlobalAnsi( name );
m_HasString = true;
m_StringDataSize = name->Length;
GC::AddMemoryPressure( m_StringDataSize );
m_Handle = reinterpret_cast<D3DXHANDLE>( m_StringData.ToPointer() );
}
void EffectHandle::Destruct()
{
if( m_HasString )
{
Marshal::FreeHGlobal( m_StringData );
GC::RemoveMemoryPressure( m_StringDataSize );
}
}
So. Do you see where we screwed this up?
In case it's not clear:
* EffectHandle::InternalHandle returns EffectHandle::m_Handle
* D3DXHANDLE is a typedef for char*
* Although there's plenty of interop, the interop is NOT the root cause.
HINT: EffectHandle is finalizable. Answer is in comments.
| |
| Tuesday, September 29, 2009 |
| Oh hell yes. | |
Posted - 9/29/2009 8:39:15 AM | 
| |
| Thursday, September 24, 2009 |
| Revolution, Part 2: BioReplicant Animation | |
Posted - 9/24/2009 11:52:13 PM | I promised this a long time ago, and here it is. I prefer to let the video speak for itself. This is a demo from January, so it’s actually a much older iteration of what we’ve got now.
Link!
| |
| Friday, September 18, 2009 |
| Our iPhone/iPod Touch game is out! | |
Posted - 9/18/2009 5:31:06 PM | Link
I'll concede it doesn't look like much, but honestly, the game is really addictive and fun. And it's a dollar.
One of the technologies in this is the binaural audio system that I discussed earlier. On the above page, there's a linked video -- put on headphones and watch it. You'll get the point very quickly. It's even better in-game than in the video, was my experience.
There's also the animation system, which is not really shown off that well here, but it's procedurally constructed, like NaturalMotion (but better, we believe). At no point were any animations build in a modeler. It's all done dynamically using relatively simple rules. The future games will leverage this tech more heavily, but at least as developers I think you can appreciate how awesome that is. The flying, the hits -- it's all physics based.
Did I mention it's a dollar? Try it out. And if you do try it out, please take the time to write an honest (and hopefully positive!) review. It'll go a long way for us if you do.
| |
| Windows API Code Pack -- Is It Any Good? | |
Posted - 8/21/2009 6:29:29 PM | This post is a late copy from Ventspace.
Just to be clear, I'm restricting my comments to the DirectX section of the codepack. I'll probably be integrating some of the other bits (jump list support etc) into SlimTune, so we'll see how that goes later. But around a week ago, they finally released 1.0. Same day as Windows 7 was out on MSDN actually -- I'm pretty sure that's not a coincidence. SlimDX's release with DX 11, Direct2D, and DirectWrite should come later this month, if all goes well. Now, the code pack does cover a few things we don't, like the Windows Imaging Component.
So it's not beta anymore. Now, I'm fairly sure that they haven't looked at our code for legal reasons, but I did make some harsh comments about their work. They've made some changes that seem to follow directly from those comments. I'm about to make some more. I've been perusing the release and frankly, it's just not any good. They seem to have spent most of their time implementing equally shoddy support for D3D 10 than fixing the actual problems. I'm going to run through all the reasons I see that this thing is not well done.
Okay, so they added a math library. I very pointedly slammed them for not having one in the 0.90 release, so let's start with the bread and butter of graphics -- Vector3F, as it's called in the Code Pack. It offers X, Y, Z, Normalize, NormalizeInPlace, static Dot, static Cross, operator +, operator -, and (in)equality comparisons. Yes, that's the entire class. No ref overloads, which are important for performance. No other helper methods of any kind. No PropertyGrid or System.ComponentModel compatibility. Matrix is even sadder -- it has operator * (by-value only) and Identity. That's it. Compare to ours, or XNA.
Functions that return object references still create brand new instances, which then not only have to be garbage collected, but if you don't remember to Dispose them, they'll be queued for finalization too. (These USED to be properties...it's an improvement, I guess.) This is a similar effect to the original MDX's event problems, just smeared out over time and difficult to track. There's certainly no leak tracking functionality like SlimDX has. (OTOH they will be released eventually, which SlimDX does not promise.) These are lots of small allocations, which the .NET GC is good at handling, but if you don't remember to Dispose them, or have a lot of them in general, this could really sour your day. It's a problem that just doesn't exist in SlimDX.
As for 64 bit support, it's simply not configured at all in the solution (remember, the code pack is source code only, no binaries). I set up and ran an x64 build that went off without a hitch, and there's no inherent reason for x64 to not work. I haven't tested it though, and neither has anyone else apparently.
Lastly, even though they've added D3D 10 support, there's no D3DX support in here at all. They basically invite you to go ahead and write what you need yourself, but none of it is done for you. For something that's intended to make your job easier by letting you use managed code, this is another odd omission.
The 1.0 of the code pack IS dramatically improved in several respects -- 0.90 had no math code at all, the memory situation was far worse, etc. Even so, this really doesn't inspire a lot of confidence. Although the core APIs are wrapped, the support code is basically non-existent. There's no binary distribution or redistributable, so you're on your own there. I know this is probably a small team at Microsoft with nowhere near the level of resources it needs, and I'm sorry that I'm continually trashing your work. But if this is what constitutes the successor to Managed DirectX, I don't think SlimDX is in any danger and I can't say I mind.
| |
| Thursday, August 13, 2009 |
| SlimTune Profiler 0.1.5 Released! | |
Posted - 8/13/2009 7:57:24 PM | Let's recap. For about two months now, I've been working on a brand new profiling tool for .NET, C#, CLR, and all that jazz. It's open source, completely free, and supports frameworks 2.0 and later (no 1.x, sorry). Some of the notable features include remote profiling, real time results analysis, and multiple visualizers. Today, the first public release, version 0.1.5, is available to the public.
Project Homepage
Direct Link to Installer
Although this is still an early version, it is already quite capable. It supports sampling mode profiling for both x86 and x64 applications, and provides views that will be familiar to users of NProf or dotTrace. Speaking of NProf, it's my belief that this completely replaces it for .NET 2.0+, with a better UI and more features too. (And a far more lenient source code license as well.) There is still a lot to come, of course, but with this release I finally feel that this is ready for the general public.
I'm looking forward to getting lots of feedback, both positive and negative, and I hope that this is a useful tool for everyone.
(P.S. If you want to build from source, you'll need to do it with a non-express version of VC++ 2008 SP1 and VC# 08, with a full boost installation. Also install the SQL Server Compact redist, which is in the repository under trunk\install\ExtraFiles.)
| |
| SlimTune's Hybrid Mode | |
Posted - 8/8/2009 11:58:33 AM | I decided to try out the dotTrace Profiler, which runs $200 for a personal license and $500 per developer for organizations. IOW, it's expensive. That $200 license makes it the cheapest of the commercial options, and I ran the trial on one of my games. They have some nice UI touches I like. The data is valuable as well -- I would not have guessed that my MainGame.Update function takes five billion percent of total program time.
Generally speaking, profilers operate in one of two modes: sampling (statistical), and tracing (instrumenting). Sampling operates by suspending the process at high frequency and examining the program state. It converges to a decent overview of where your code is spending time, but it doesn't produce meaningful timing information. The frequency simply isn't high enough. Tracing injects calls to the profiler every time a function is entered or exited, allowing it to monitor the complete progression of your code. You get accurate results with fairly reliable timings, but it's incredibly slow. (Oh, and it crashes dotTrace. People pay for this?)
I've been looking at doing a hybrid mode since the beginning of the project; I finally came up with a concrete approach when a friend gave me a rough overview of SN Tuner, the profiler for the PS3. The idea is fairly simple: you don't generally want tracing-level accuracy for the vast majority of the code. All you really need is an overview, which sampling does a good job of, and then tracing when you're focusing on one specific piece. You also don't really need detailed profiling of framework code (everything in System, for example). Although I'm still working on the front-end, SlimTune is now able to do this type of selective instrumentation at runtime.
Using it is pretty simple. When you start up the target, select Hybrid in the SlimTune UI. This will cause the program to run in sampling mode, and you'll get your overview results. Then, you can select a function from the overview and ask it to be traced, and then results will flow in from that function and its children only. You can also turn it off again, and you can ask for entire namespaces to be skipped in either tracing or hybrid mode. Hybrid mode is a little slower than sampling overall, but it allows you to get very detailed results without the huge performance hit that normally accompanies that level of detail.
Internally, it's a little tricky to pull this off but it's not too bad. I discovered early on that taking a lock on the function hooks is hideously expensive, even at zero contention. I use a few lockfree tricks to get the necessary data much faster. It's also very important not to let the sampling profiler attempt to sample inside the hooks, as this leads to some nasty deadlocks; again, lockfree code is used to lay out some unsafe zones that the sampler can detect and avoid. SuspendThread is one messy son of a bitch.
So there are at least three features I'm giving you for free which a five hundred dollar competitor doesn't have. Sure they have a much cleaner interface, VS integration, memory profiling, and so forth...but I've only been doing this for a month. Kinda makes me wonder. Oh, and guess what I spent the last day or so doing...
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