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Member Since 05 Apr 2006
Offline Last Active Jun 20 2015 10:14 AM

#5210472 Entity-Component Confusion

Posted by on 13 February 2015 - 08:06 AM

What confuses me though is how do you store the component in an efficient way? My understanding of the entity-component system is that it simplify things, and reduces cache misses, right?


I have similar topic http://www.gamedev.net/topic/662559-entity-component-system-data-locality-vs-templates/ and I was directed to this bitsquid blog that I found very helpful. Making a manager for each type of component avoids problems with storing inhomogeneous data in arrays. I also liked their idea not to constrain the component managers that much. Different type of components may benefit from different type of component storage and entity<->component indirection. I personally would create base component manager classes for some most typical situations to avoid code dublication.


I.E. When a player shoots a ship, and the ship is now dead. It should be removed. So it's flagged as such, and at the end of the loop, it gets removed from the list, and everything gets shifted down to keep data clustered tightly.


Use the "swap and resize": move the last item to the place of the removed one and reduce the array size by one. Of course if entities refer directly to component arrays, the one moved component will no longer point to the correct entity. You need to add a layer of indirection: one array stores components, the other maps entities to the components.

#5205851 Quick texture array question

Posted by on 21 January 2015 - 03:07 PM

Which doesn't work. The shadow map doesn't seem to be accessible. Again, the texture array on its own is working fine, and the shadow map, when bound with individual textures, works fine as well. But, when I try to use the shadow map, while using an array for the other textures, things aren't rendering properly. To be clear though, there are no errors reported, but the shader is clearly not reading the shadowmap correctly.
If this code looks relatively fine, then my issue is likely elsewhere.


The code looks fine to me as far as I can interpret it without further information. Are you sure that your uniform ids are properly resolved? Are you binding the shaders before calling glUniform etc?

#5205734 Quick texture array question

Posted by on 21 January 2015 - 02:56 AM

As NumberXaero suggested, you bind the array to one location, say 1:

glBindTexture(GL_TEXTURE_2D_ARRAY, texturearray);
glUniform1i(location, 1);

In shaders you use

uniform sampler2DArray arrayTex;

/* ... */

void main()
 float index = 0.0;
 vec4 color = texture(arrayTex, vec3(texCoord.xy, index));
 /* ... */

The third component of the second argument to texture is the array index. Arrays are great for overcoming texture image unit limitations, although the layers will need to have the same properties

#5205487 Projection into Spherical Harmonic Basis

Posted by on 20 January 2015 - 01:56 AM

My understanding is that I should be able to just multiply each of my function's samples with the basis functions evaluated at the sample's XYZ direction, then accumulate the results to get a SH expansion for the function samples.


Practically, yes. In the continuous formalism, the expansion factors a for function f are obtained by

<img src="http://www.codecogs.com/eq.latex? a_{lm} = \int_0^{2\pi}\int_0^\pi Y^*_{lm}(\theta,\phi)f(\theta,\phi)sin(\theta)d\theta d\phi" />

Where the sin factor is the Jacobian. You can use which ever numerical integration you find most fit. For smooth functions, you could use the Simpson rule for both angles in a nested way. This is enabled by the Fubini theorem for smooth integrands. You might also use Gauss family of quadrature (e.g. Gauss-Legendre) to reduce the number of evaluation points.


My question is, how well will this work if I only have a few samples of my function, possibly with irregularly spaced samples? Will the SH basis smoothly interpolate just a few (e.g. 3 or 4 values) samples, or do I need to do a monte carlo integration scheme where I sample a separate function that uses the nearest sampled neighbor for the query direction.


I don't know the precise answer to this, but what you are most likely doing with SH basis is not interpolation, but approximation. When you evaluate your function in the truncated SH basis, there is no guarantee that it will interpolate your sample points. If you have only a few samples, you probably get aliasing issues as with the more traditional Fourier series.

#5204199 Multiple Lights on game map with forward rendering

Posted by on 14 January 2015 - 07:38 AM

How is your game map different from a collection of objects? Is it a terrain or some unstructured mesh? Anyway, why not split the map into smaller pieces. Then determine the four most important lights for each pice. Do you anticipate that there will be more than four lights that significantly influence small portions of the map?

#5195189 Resource manager for open world game

Posted by on 28 November 2014 - 08:11 AM

The pseudo-code above is very high-level and just an example. But you got the idea. As with the reference counter and as your should know you must find a way of avoiding hash collision. Actually since you're talking about loading time, this is not a problem to compute because you're loading all resources. If you was doing this while playing the game you could have into problems.


Thanks for the example. Your approach of invoking TextureContainer to get the texture seems fine. In my code attempt, the handles store pointers to managers that created the handles, and then the rendering code can call handle.getData(). There are probably pros and cons in both approaches.


I'm not sure why you mention hash collisions at this point. Anyway, I'm not worried about those. In fact, I'm not convinced I should even use hashes. I could just use directly the names of the resources instead, since seeking the handles by name does not have to be that fast. With "one manager per resource type" there is no fear that sound "fire" is mixed up with particle system "fire".


I don't think that loading resources during game play will be a problem if utilizing handles. In your code, Get() method would just return a dummy texture until the actual texture has been loaded. I also tried to sketch this in my code. Of cource in practice is not very nice if an ogre mesh right in front of the camera is shown as a dummy teapot mesh while the ogre is still loading, but it's better than access violation. The game or higher level engine routine should take care that resources are loaded sensibly.

#5195173 Resource manager for open world game

Posted by on 28 November 2014 - 07:11 AM


The general case manager I use for a lot of things works well.


You just need to add a reference count to each asset.


So something along the lines of.

public class AssetManager
       Dictionary<Hash,AssetType> loaded_assets = new Dictionary<Hash,AssetType>();
public :
       Asset AddAsset(String name)
              if (loaded_assets.Contains(name.Hash))
                    loaded_assets.Add(new AssetType(name));
              return loaded_assets[name.Hash].Asset;
        void RemoveAsset(String name)
                if (load_assets[name.Hash].ReferenceCount==0)




Implementing reference counting is one part of a manager, but perhaps c++11 smart pointers would do a better job if one is only worried about this aspect. I guess that your manager is only supposed to add reference counting on top of dictionary. Some further remarks:


- Your code clearly takes the path that there'll be one manager per resource type. That's already a major desicion. I would like to hear more experiences whether this tends to work or not in games that have many types of resources.


- Your manager directly returns the asset data, not a handle. Another big desicion, which I think won't work well if the manager decides to move that data in memory or the data is destroyed and a dangling pointer remains.


- There seems to be no way to actually load the resource. Or is the idea that after invoking AddAsset(), the asset is loaded? There would have to be some way then to know if it was already loaded.


- It does not seem robust that to remove a resource, one has to call a method of the manager. If some game object using a resource is destroyed, it will have to signal the manager that the resource is not used anymore. Injecting manager dependency to game objects does not seem natural.

#5185116 Is upper division Linear Algebra a good idea or necessary?

Posted by on 05 October 2014 - 07:27 AM

They're all useful. Number theory tends to be a little more essoteric, but is useful for understanding things like the minimum number of bits needed to store (complex) information, or, in understanding how much accuracy you can rely on maintaining through a series of floating-point operations (and strategies to maximize accuracy by ordering operations differently).

The exact cource contents vary between colleges/universities but usually Number theory is about integers, e.g., prime numbers and such. In my university, a course that deals with floating point approximations of real numbers and the like is named Numerical analysis.

#5180637 Advanced heightfields in Bullet physics

Posted by on 16 September 2014 - 01:19 AM

At the moment I'm using Bullet for physics and collision detection with a basic heightfield terrain. The heightmap is 2048*2048 and so cannot yield very high resolution for my roughly 8 km x 8 km terrain.


I'm using a vertex shader for some portions of the terrain, which locally masks another heightmap, which is repeated 100 times, over the terrain. The heightmaps and mask are read in vertex shader to displace the terrain grid. The grid itself can be quite dense, so that the additional information from the masked heightmap is visibly utilized. This way I can achieve nice bumpy appearance for, e.g., forests and fields.


The problem is communicating this masked heightfield to the physics part of the game. My quick hack was to make a higher resolution map, say 4096x4096, where the two heightmaps are combined, and pass it to the Bullet physics. Of course this has still insufficient resolution in some cases and it wastes memory.


I started wondering if it would be easy to modify Bullet's btHeightfieldTerrainShape.cpp module to allow for such additional masked heightmap. A quick look gave me the idea that Bullet just samples the given heightmap on demand and doesn't do any costly pre-processing or caching. This suggests that I could add my masked heightmap easily by modifying getRawHeightFieldValue function and storing the other heightmap and mask in btHeightfieldTerrainShape. Can anyone confirm this?


Another related topic is that in the future, I may want to divide my terrain into, say 1 km x 1 km blocks that have their own heightmaps. The heightmaps would then be stored at varying resolutions and streamed from the disk. I would need to be able to update the Bullet heightfield quickly after a stream is complete and this requires that Bullet does not do any heavy processing on heightfield updates. Has anyone experience with anything similar?


Thank you in advance.

#5171358 multiple source files and global varaibles.......................

Posted by on 04 August 2014 - 12:49 AM

I recognize that you are still learning basic programming, but I still would like to give one design hint: don't use global variables. It will eventually lead to errors that are very difficult to trace and it will also make the code difficult to read. For instance, if I take a look at Function.cpp and its function clip_tiles(). It seems to reference the array clips, but it is not at all clear to the reader where this array is defined. Try to construct your functions so that they only act on the given arguments and have no reference to global things, except for global constants. Global constants are ok.


I remember the time when I was a beginner programmer and global variables seemed like an ok way to do things (I had also Basic background). I though it was impossible to write a big real life program without global variables. Boy was I wrong. It's very much possible to construct your game with something like

int main()
 CGame game;




 return 0;

No globals needed, everything is contained in class CGame. Some might say that this is not the best approach either, but it is certainly an improvement to using a number of global variables.

#5164871 object space normals and skinning?

Posted by on 05 July 2014 - 07:35 AM

I'm using object space normal maps with skinned meshes and at least I think it works just fine. 


I pass an object space light vector to the vertex shader. This is then more precisely in the object bind pose space. Then I transform that by the transposes of the bone matrices (which transform from bind pose to skin pose) in the vertex shader and pass that to fragment shader, where a dot product is calculated with the object space normal sampled from a texture.


To see how this works mathematically, say that n is object space (bind pose) normal and L is light vector in the object space (also bind pose). Let S be a bone matrix for one bone that transforms from bind pose to skin pose. We want to evaluate dot(Sn,L). This is just dot(Sn,L) = dot(n,S^T L). This is done for all bone matrices that affect the vertex in question and a weighted sum is calculated.

#5029019 +4 bones vertex skinning

Posted by on 05 February 2013 - 07:00 AM

I'm confused. Is was under the impression that in fact this is the "bind pose approach" - these weight positions are provided only in bind pose (scratch that, they are pose independant, they only inform about mesh "volume", combined with bones, bind pose or not, they give the final result) and I also have bind pose skeleton provided. So how do I get rid of these weight positions? What's the usual approach here? Right now I have bind pose skeleton but in fact I don't use it while animating. It's only helpful when "unpacking" animation (skeleton) frames but it looks like there's a reason it's there. I have no idea if Doom3 uses these weight positions in shaders. I just followed mentioned tutorial and ended up here.


I animate MD5 meshes in a way C0lumbo implied. Post multiply your animation pose matrices with the inverse bind pose. Then you can just send the bind posed vertices to the GPU.


I'm not sure how animating is done in Doom 3, but maybe it is possible that they did not use GPU skinning, because they needed the transformed vertices for constructing shadow volumes. Then it should be faster to have the vertices in weight space so that post multiplication by inverse bind pose is avoided.

#5029016 Trouble with very slow rendering with nvidia under Linux

Posted by on 05 February 2013 - 06:52 AM

Which drivers are you using? The default open source drivers have poor 3D performance, so make sure you have the nvidia's closed drivers installed.

#5021147 Losing interest in game development...

Posted by on 13 January 2013 - 12:15 PM

I can relate to this topic very well, and I can share bits of my story:


Game programming has interested me ever since I got my first computer. At the beginning of high school, many years ago, I started learning OpenGL and more advanced graphics techniques. With a few friends, we started a very ambitious first person shooter project with very little experience. I thought I could implement all the fancy stuff I read about, such as per-pixel lighting, dynamic shadows and so on, even though these were emerging techniques at the time and robust implementation was very challenging. The focus started shifting more and more towards making a 3D engine, not a game. I wrote a lot of code. Not having a good idea of how things will eventually connect, I often ended up with a bloated and non-inspiring code base. Then I rewrote all. Then I rewrote all again. And again.


There were many times when I just fed up with not completing the engine or a game and I decided to stop. Designing and programming games, however, always kept lingering in my head, and eventually I have returned to the topic.


Two years ago, after having some break again, I decided that I will start a new 3D game project and I will keep it small and finish it. I wanted to have something complete to show that I can do game programming. The project is still under active development, but I managed to keep it graphically very simple at the beginning, and actually wrote a lot of game related stuff. Then I succeeded in having a playable version running, before starting to add fancy graphics. This is what I should have done many many years ago. But I think I learned a huge amount of stuff and I learned what it will take to implement certain techniques. So when I started this particular project from scratch, I had a pretty good idea how things work.


I guess that the thing about game programming and programming in general, that keeps me being interested in it, is that you can be creative. You can come up with some cool idea, design it, code it and when you get to see your creation, the feeling can be very satisfying.


The other thing, that pinebanana also brought up, is deciding the level to work on. There are so many game and graphics engines, that making your own from scratch can be difficult to justify. Of course, if the aim is to learn and if the game does not need that much technology, making most of the stuff yourself can still be reasonable. But to me it seems that saying "I made this game all by myself" might carry a different weight depending on just how many libraries I used or if I used an existing engine.


I'm not sure If it is a problem for any of you guys, but to me it has started to be increasingly important that a code and a program is usable after, say, 10 years. It seems that 3D graphics schemes and API:s evolve at a huge pace, so ensuring future compatibility can be difficult. If I doubt that the code might not compile or  the program might not run in the near future, this is a major discouragement.

#4986302 Improving Terrain Textures (getting banding)

Posted by on 03 October 2012 - 12:35 AM

I've also been working on terrain texturing lately and the greatest problem has been avoiding noticable tiling. Basically I have an array of textures, four noise channels and a mask for up to four "painted" textures. In addition to these pained textures, there is a base texture, cliff texture whose weight is determined by slope and a shore texture whose weight is determined by height. At the moment, I use two slightly different texture maps for each texture type and use carefully chosen noise to mix these. This gives quite nice results and makes tiling quite difficult to notice, but the noise must be well adjusted. The noise should be quite high contrast and patches of 0.0 and 1.0 should occur on the scale of the texture period. I basically used a cloud filter in Gimp and made the contrast higher.

Previously I tried mixing the same texture with different scales. This made tiling much less apparent, but it also makes the texture fuzzy and close up detail is pretty much lost.

As to the banding, it seems that you use slope to smoothly blend between textures, but a strict if condition to switch textures by height. Make some transition height ranges to smoothly blend by height. Insted of if(heightPercentage < 0.05f), define two height values around 0.05f and interpolate two textures along these values.