XBox HLSL Peculiarity

While fiddling with my shadow code to try and get more reliable performance on the Xbox I changed my HLSL shader code so I could quickly make changes to a pair of nested loops that calculated the weighted average.

Most of the testing was done on the PC and it all worked fine.  When I tried it on the Xbox the shadows had completely gone!

It took a while to find but it was the simplest code possible that did not work on the Xbox but worked perfectly on the PC.

 float shadowTerm = 0.0f;
 int sampleCount = 0;
 for (float y = 0; y <= sampleRadius; y++)
 {
   for (float x = -sampleRadius; x <= sampleRadius; x++)
   {
     float sample = something();     
     shadowTerm += sample;
     sampleCount++;
   }                      
 }    
 // Average by the number of values
 shadowTerm /= sampleCount;
  

That code does NOT work on the Xbox.
Note the sampleCount immediately following the shadowTerm in the middle of the loop.
What could be simpler code.

Take it out and replace with a sum at the end after the loop and...
the following code does work on the Xbox!

  float shadowTerm = 0.0f;
  for (float y = 0; y <= sampleRadius; y++)
  {
    for (float x = -sampleRadius; x <= sampleRadius; x++)
    {
      float sample = something(); 
      shadowTerm += sample;
    } 
  } 
  // Average by the number of values
  shadowTerm /= 
        (sampleRadius + 1) * 
        ((sampleRadius *2) + 1);
  

If anyone has a reason other than the compilers are different, please let me know.

3D Modeling Tools

I've just read a comment on one of my other posts asking about what I think about the free modeling tools available.  The reply to the comment became too long so I decided to reply by way of this post.

Despite how my blog may appear, I'm not as confident about 3D modeling as I sound.  I've just been learning it for nearly two years on and off so have some experience!  Based on my school results some 30 plus years ago, I do have an aptitude for technical drawing.  I think that helps a bit.

The type of models I produce tend to be architectural.  When it comes to more organic shapes I have to get others to do those.

About 2 years ago I tried most of the free modeling tools.  Some were difficult to use, some too simple for game models and for some there were no working FBX or DirectX exporters suitable for XNA.  I ended up with just three that I gave any serious time to.

I had a brief look at the commercial products but the popular ones used throughout the professional games industry have a price tag of about US$ 3,500.  I suspect that a lot of the people using those for Indie games would be the first to complain about their game being pirated!   Some hobby developers can get away with educational licences.   I want to distribute my game for the Xbox which Microsoft have forced to have a price tag.  Therefore any game released for the Xbox is commercial, no matter what the intention or how low the cost is.

That left me with the shareware, open source or free products.  Without much effort it is easy to establish that by far the most fully featured, continuously developed and suitable tool is Blender.  I have never used 3DS or Maya but from what I can tell Blender is as powerful and in some areas probably more feature rich than those paid for products.

Blender is a powerful tool but like nearly all complicated products it requires quite a while to master.  Having tried it and become very lost, especially with a non-Windows style interface, I looked at other products first.

The three tools that I had reduced my list to were, the free Autodesk Mod Tool, Blender and the free version of Google SketchUp.

To quickly dispense with one of those, Mod Tool.  I tried it, found it's pipeline so confusing I could not work out how to export a model and the whole layout just put me off.  I think but didn't give it much of a chance, that it attempts to simplify some of the technical details about 3D modeling but in the process loses the plot!  I have not looked at it since.

The product I do like is Google SketchUp.  I have only used the free version and I have not spent much time using version 8 but I did use version 7 quite a bit.  It is very quick to learn and easy to produce buildings and things.  The interface is very natural to use.  I wish more powerful tools had this simple and well thought out UI.

For XNA there is a snag with the free SketchUp.  It does not come with any suitable exporters!  The official FBX exporter only comes with the paid for Pro version.  However, if you hunt long enough on the Internet you should find some third party FBX exporters that work with the free SketchUp.  Also SketchUp files are just compressed Colada files and Autodesk do a free converter from Colada to FBX.

SketchUp gets tricky when you want to have more controls to optimise the result for use in game.  Controlling the UV map to minimise the number and sizes of textures or reducing the number of vertices is tricky and may not even be possible in SketchUp.  It's at these times that I kept ending up in Blender to finish a model.  Also I have no idea if SketchUp can do boned animations which I need for my game.  Another plus point for Blender.

Once I had decided that I would need Blender, I spent two weeks just learning the very basics.  Remember I was learning both the product and 3D modeling from nearly scratch.  Over the last two years I have watched numerous tutorials on line and have even purchased two Blender training DVD's.  I also laminated the Blender Hot Key chart and have it permanently to hand.

What I now have is a huge respect for 3D artists.  There is no quick fix that us developers would like.  As a developer I think nothing of spending hours on one small method to get it just right.  That time and more goes in to the fine detail of each good model and each texture on those models.  The work on some of the individual models in AAA games must be as much as I have spent modeling... ever.

All modelling tools, except perhaps SketchUp require a lot of practice to be able to work with.  I decided to concentrate on knowing just one rather than a little about all.  I now almost exclusively use Blender.

Blurring Variance Shadow Maps

Before we get too far, let me point out from the start I have not got this working!

This is the original Variance Shadow Map (VSM) article I have been reading:
http://developer.download.nvidia.com/SDK/10/direct3d/Source/VarianceShadowMapping/Doc/VarianceShadowMapping.pdf

This is one of several Gaussian Blurs I have tried:
http://www.dhpoware.com/demos/xnaGaussianBlur.html


The process sounded simple.  Take the RenderTarget for the shadow map.  Apply the blur in a shader and use that blurred shadow map to render the scene.

Well after lots of late night fiddling with samples and blurs, and after solving the errors about Vector2 requiring Point filtering I still get blurred shadows that are too blurred at the wrong edge where it should be solid and still pixelated at the shadow margin where I want it blurred! 

If anyone knows what important information I am missing, please post a comment telling me how.

I have stuck with my edge filtering for now and intend to try ID based shadow maps next.

Revisit Shadows

The inclusion of the new model in my first scene highlighted limitations in my shadow effects.  Shadows from overhangs and concave objects were stretched down vertical faces producing rough unsightly and distracting shadow margins.  Particularly when moving.

Most shadow maps produce waving edges but the trick is to make them so small that they are not noticed during normal game play.  Mine were unfortunately very noticable in some situations!

I have plenty of other things to do and should have left it but I could not and had to make an attempt at fixing it.

My first attempt was to change to using variance shadow maps (VSM) instead of single depth based with percentage closer filtering (PCF).

VSM uses both the depth and the depth squared and some maths to minimise artifacts caused by the depth buffer being of insufficient resolution.  It avoids the need for a shadow depth bias value.  Much to my surprise it was easy to drop in to my most recent shaders.  VSM works very well.  I am unlikely to go back to PCF.

VSM did not solve my problem.  It removed other artifacts and gave me a much crisper edge but that margin was still stretched and unsightly!

As a quick fix, I used the edge tap smoothing code from my PCF methods.  That worked to reduce the sharp edges but the margins were still too big.  The solution, which I could have also done with my PCF code was to increase the number of samples.  I was using 3x3 samples, I tried 5x5 samples.

As you can see from the picture not a bad edge.  I was happy with that.

Unfortunately there was still a problem...   When I tried it on the Xbox, it could not cope!

The frame rate dropped a bit but worse it just stopped texturing some surfaces!  Aaaaah!

I dropped it to 4x4 sampling, that worked on the Xbox but I was not happy with the shadow margin again, too pixelated!  I had and still have loads of time consuming things I could try to impliment but I had another problem to solve which has given me acceptable results.

The concave objects that were causing me problems had light bleeding near all the inner edges.  I wanted to pull the shadow towards the corner to use more of the dark area and less of the light area.  To do this I wanted to offset the area used for the weighting so it was not central but based on the colour away from the light.

Much to my surprise this solved two problems.  My 5x5 samples became 5x3, 25 down to only 15 samples, just about workable on the Xbox.  Plus the light in the corners of concave objects was reduced to a more acceptable level.

I am not claiming that the results are perfect.  I am learning this as I go along, so there is little hope that I will ever get to AAA game levels of detail.  The results are now acceptable to me although the frame rate on the Xbox is still a little poor.  The wavy edges are no longer distracting during normal game play.

The end result is still a bit stretched and the offset sampling results in an uneven blurred edge but this is for a fast moving shooter not an atmospheric spooky adventure.

I have to have two different quality shaders to get an acceptable frame rate.  A lower number of samples on the terrain (3x3) and a higher number of samples on the structures (5x3) to get the better stretched vertical margin.

You have to get pretty close to see all this and if you did that in a game someone would have shot you by now :-)

Now I just need to try blurring the VSM instead...

http://developer.download.nvidia.com/SDK/10/direct3d/Source/VarianceShadowMapping/Doc/VarianceShadowMapping.pdf

And In The Game...

The hut model in the game.

And Textured...

The finished hut.

Just need to make it one mesh to improve performance and export to XNA.

Developer Art

This weekend I've been working on one of the buildings for Diabolical: The Shooter.

It is a building that will be in the first scene.  Archaeologists digging for alien remains were living in the these demountable buildings.  Several of them will form a small encampment.

I did the concept art a week ago.

Yesterday afternoon and this morning I worked on the mesh using Blender.

Next job is to add the texture.  If I decide to do all the models myself, at one a week, it is going to take a very long time to get the game out.  For more generic items I may have to purchase some finished models to speed things up.