Sponza scene (direct + indirect lighting w/ occlusion)

Sponza scene (only indirect lighting w/ occlusion)

Sponza scene (ony direct lighting)

Sponza scene (boosted indirect lighting w/ occlusion)

Sponza scene (boosted indirect lighting w/o occlusion)

The algorithm approximates global illumination by rendering the light into a reflective shadow map, injecting it into a volume (using a spherical harmonics representation) and propagates the light flux in this volume (hence the name of the algorithm) and taking into account occlusion as possible extension.

The whole algorithm is physically motivated but corners everywhere, of course, to be more efficient. The paper also contains a few errors and doesn’t explain everything needed to implement it in great detail (like eg the solid angles of the side faces), so I’ve written two documents detailing the mistakes I’ve found and the additional calculations I’ve performed.

You can find the mistakes here (including suggested corrections) and the full annotations document here.

Finally I’ve also uploaded the whole prototype (including my code licensed under the FreeBSD license and the media files) here – it’s 68 MB big (and it’s been compressed with 7zip with a compression mode that might not be supported by WinZIP. The Sponza model is from Crytek, too. You can download the original model and textures here.
The project uses DirectX 10.1 and by default it won’t run in DirectX 10, because it uses a texture format that is deprecated in D3D10 but supported again 10.1 (BGRA). See the comment by FatGarfield for the location that needs to be changed for it work in DX10, too. (However red and blue will be swapped then.)

I haven’t implemented cascaded LPVs and I also use only one light/RSM and only inject its depth into the occlusion volume, but the results already look very nice in my opinion.

Stay tuned for more
Cheers,
Andreas

Here is the code dump: PanoramaStitching.zip

It contains many small projects which usually use multiple pictures as inputs or multiple webcams (depending on code or chosen preprocessor macros).

The most advanced prototype is the SnapshotHomographyConfigurator, which allows you to determine homographies between multiple cameras at once by marking shared points between the images.

Another one which works okay is the PanoramaStitching project. It creates panoramas using spherical or cylindircal projections of the input images. However, it is very sensitive to translations of the viewpoint. It works quite well with optimal/artificial images:

(Note: the small misalignment on the right stems from moving the player position slightly. Usually you use a deghosting algorithm to remove such misalignments.)

I’ve used OpenCV for image processing and yaml for loading and storing settings (and also rapidxml). OpenCV’s C++ wrapper is pretty awesome. It’s not perfect but it makes life a lot easier.

Stay tuned for more code/project uploads soon

PS: Here are the links to some papers which proved useful to me (I didn’t implement most of them though, and some are implemented in OpenCV already):

• Eliminating Ghosting and Exposure Artifacts in Image Mosaics
• Pyramidal Implementation of the Lucas Kanade Feature Tracker – Description of the algorithm
• Image Alignment and Stitching: A Tutorial
• Seamless Image Stitching by Minimizing False Edges
• Construction of Panoramic Image Mosaics with Global and Local Alignment
• Image Mosaicing for Tele-Reality Applications
• Good Features to Track

Below is a visualization of the first 4 bands of the SH basis functions (created using Mayavi):

The first 4 bands of the spherical harmonic basis functions

As you can see the first two bands are 4 functions, so 4 coefficients to store which conveniently fits into one RGBA texture.

One of the main transformations that is performed in the LPV paper is the rotation of the spherical harmonics representation of a clamped cosine lobe (that represents surface lighting) onto a normal vector direction.  It took me a while to figure out, but actually it’s quite easy, which is why I write about it

The analytical presentation of the first four base functions is simple:

To evaluate lighting with SH for some direction v, you first determine the coefficients/weights of the SH basis functions and then sum them up.

Let’s assume we know the coefficients of the clamped cosine lobe around the z axis, then we can determine the lighting in direction v for the cosine lobe around the normal n by transforming it into the space where the normal coincides with the z axis (ie rotate n onto the z axis):

where is a rotation matrix that rotates n onto z.

The idea is to expand and rewrite it in terms of .

Before doing this, let’s first take a look at the coefficients of the clamped cosine lobe:

The y and x direction are 0 because the cosine lobe is centered isotropic around the z axis:

So let’s look at the expanded version of this formula if , , are the row vectors of the matrix,
and , then:

Since and :

Now the question is: what is the third row of ? If we look at the inverse matrix instead: , we can immediately see that its third column has to be n, because by construction. Since rotations are orthogonal matrices, the inverse is the same as the transposed, so we can deduce that the third row of is the same as the third column of ,  that is: n. Thus with we get:

So the SH coefficients of the clamped cosine lobe along n are:

This is it

Cheers,
Andreas

PS: a few screenshots from the LPV project:

Here are two versions of my presentatio (one with less text and one with more):

Rigid Body Motion Presentation as PPTX; Rigid Body Motion Presentation as PDF
Rigid Body Motion Full Version as PPTM; Rigid Body Motion Full Version as PDF

If you are truly interested in learning about rigid body physics, here are some books/links:

• “Technische Mechanik 1 & 3” by Gross, Hauger, Schröder & Wall
• “Physically Based Modeling” by Pixar (SIGGRAPH 2001)
• “Mathematics for 3D Game Programming & Computer Graphics” by Eric Lengyel
• “Physics for Game Developers” by David M. Bourg
• “Game Physics” by David H. Eberly
• Chris Hecker’s Rigid Body Physics page

Cheers,
Andreas

I’ve also finally added a project page for it to this blog.
More updates might follow soon if I find enough spare time
Cheers,
Andreas

I’m currently preparing for a math exam (calculus) and I’m thinking it would be nice if there was a way to avoid much of the “for every there is an , so that for all some property … holds” stuff you find in textbooks. Some textbooks actually shorten it to “for every some property … holds for almost all “.
However, I haven’t found a quantifier to express this anywhere yet, so I’m proposing to introduce a new one:

should mean “for almost all holds”, which suggests that there are only finitely many elements for which it does not hold.
One can formalize this as:

Of course, a new existential quantifier is required then, too (for negation):
stands for “there exist infinitely many , for which holds”.
And this can be formalized as:

It’s easy to see that

Thus one can use the two quantifiers just as one would use and usually. Note however than and don’t interchange and neither do and .

One last note: it might be worth using a different notation, for example: might be easier to understand than , and might be better than .

I’ll try to formalize these quantifiers some more when I find some spare time.

Stay tuned for coding related updates soon
Cheers,
Andreas

Prototype

Gameplay is okay I guess. Nothing I would spent too much time on though. It looks a lot worse than GTA 4 though (same as Crackdown).

Resident Evil

Seems to be lots of fun and some nice graphics, too.

Red Faction: Guerrilla

Some weird texture filtering issues and the presentation doesn’t knock off my chair (terrain popping and other ugliness), but multiplayer is loads of fun with friends. Physics isn’t completely stable though. I played the game for one hour in MP with friends and there were quite a few cases where geometry dropped through the floor with enough pressure from above (after destroying a building).

Brüno

A bad and quite stupid movie (Ali G in Da House is probably the only movie I kinda like that stars Cohen). If you haven’t watched it already, don’t >_<

Shadow Complex

I bought shadow complex a few weeks ago and I have to say that it is an awesome game. I read somewhere that the developer used the Metroid series as inspiration and it shows. It’s really fun to play and quite addictive. The graphics are pretty awesome (it is using the Unreal 3 engine) and the whole presentation is pretty polished. It certainly is worth its 1200 gamerpoints

Summing Formulas

A month ago I was doing some exercises in an analysis book (Königsberger) and found a nice/interesting problem:

Prove that if we denote of the sum of the numbers 1 to n to the p-th power by , then the following equation by Pascal holds:

It can be used to get recursively/iteratively get formulas for sums of higher powers of numbers.

This is interesting because the proof doesn’t need any advanced maths (like eg the Euler-MacLaurin formula, which can be used to show this, too).

You can download the proof and a few examples here.

Cheers

People on StudiVZ share all their data by default—contrary to Facebook which values a person’s private data a lot more. Thus by simply opening each profile from a dummy user and processing the HTML data from StudiVZ one can extract a lot and some more information from random people who probably don’t even know about it or don’t care.. so I’m not sure about the stealing part.

Apparently there are some captcha’s when you start browsing searches beyond a few pages. I guess that is where the hacking part comes in, because getting around a captcha probably constitutes hacking—maybe?

Anyway I think part of the media coverage is a bit ridiculous because anyone can write a simple harvester in an hour or two. It took me one and half hours, so I think I’m on the safe side with this estimate and I didn’t really have a clue about this stuff before either.

Since I don’t want to “hack”, I’ve only written a very tame harvester. It connects to your personal StudiVZ account, and retrieves the name and profile ID (and thus profile URL) of all your friends in the “Meine Freunde” pages.

It could do a lot more with that like retrieving everybody’s birthday or random pictures, but I’m too lazy to code that because you use the same pattern for extracting data over and over again and it stops being interesting quite fast.

You can download the project here. It is a one file C# project. I’m releasing it under GPL (whatever).

It’s really easy to explain how it works:

• It uses System.Net‘s HttpWebRequest and HttpWebResponse to get (and post) web pages.
• StudiVZ (like every other portal) uses cookies, so I create a CookieContainer and use it in every http request.
• There are a few hidden values that StudiVZ expects during login. I’m retrieving them from the main page using custom built regular expressions. I’ve found a handy AJAX tester for .NET regular expressions. It was really useful for building the expressions and debugging them. (BTW you can find all URLs I used in the comments.)
• After login I use the same pattern: get page & parse using regex for everything.
• Visual Studio has an awesome “HTML Visualizer” for strings. It displays the content of a string as HTML page, which is really nifty if you’re doing anything related to HTML processing.

The code is quite ugly. Well, it’s not production code and this is only meant as a proof of concept.

Also note that I have at most violated the AGB of StudiVZ and not committed any criminal acts and I’m not planning to sell my friend’s profile IDs or data either

Maybe someone can extend the code and make it more useful. I guess it would be fun to automatically download all your pictures (including tags) and feed them into flickr or picasa… but someone else can do that.

Cheers,
Andreas

Screenshot of Utah

For the last two months I have been working on my bachelor thesis at the Chair of Computer Graphics and Visualization. It is about “Multi-Tile Terrain Rendering with OGL/Equalizer”´.
The chair has a very nice Direct3D 10 terrain rendering engine and they want to run it at the newly founded KAUST (King Abdullah University of Science and Technology´) in a massive CAVE environment. A CAVE is a room whose walls are actually screens.
The CAVE at KAUST even supports stereoscopic rendering. Thus in total 12 views can be rendered to.

My job was to port said terrain engine from Direct3D to OpenGL and afterwards to the Equalizer framework, which is an open-source framework for parallelizing OpenGL applications.

You can find/download an online version of my bachelor thesis here. I’ll upload the LaTeX at a later date and update this post.

I’ve spent the last months writing about all this, so I don’t feel like talking about the thesis itself anymore. Instead the remainder of this post will contain a post-mortem of it.

Post-Mortem

Preparations

I think I did a good job at preparing myself for the thesis: I’m a LaTex noob, so I got lots´ of LaTeX books; I’m a (paper-)writing noob, so I got lots´ of books about writing papers and writing good English.

The books have helped me a lot and it is always a good decision to get as many books as possible, because the more sources you have, the better.

I got all the LaTeX books from our university library:

• [Einstieg in] LaTeX
  A big book (696 pages) but not particularly helpful. The reviewer on Amazon is pretty much right: it contains lots of information., but always stops short of providing the really useful details/information.
• LaTeX – Ge-packt
  A small but thick pocket book (608 pages). I totally forgot I had it and it stood on my bookshelf until I found it yesterday. I’ve used it though while writing another paper last year, and it’s pretty neat. It’s a nifty reference, that’s what it is.
• LaTeX Hacks: Tipps und Techniken für professionellen Textsatz
  This book is very good. It contains 100 “LaTeX hacks” (on 416 pages). These are small, closed sections describing the solution to a specific problem you might encounter while using LaTeX.
  I’ve used the book a lot of times to look up solutions to my problems and it references many useful LaTeX packages, too—so it’s a good start for searches.
• Wissenschaftliche Arbeiten schreiben mit LATEX
  Get this book if you want to write your thesis with LaTeX. It’s incredibly useful and covers most of what you’ll need. It takes you on a journey through all features of LaTeX that you will use and describes the most common use cases. It even has a section describing how to fix common LaTeX errors like overflowed hboxes and others.

I’ve also bought some books about writing papers and the English language in general:

• A Manual for Writers of Research Papers, Theses, and Dissertations, Seventh Edition: Chicago Style for Students and Researchers
  This book covers everything you need to know about the style and format of a thesis. It has a huge chapter about how to add citations and what format the bibligraphy should use, etc.
  In retrospect reading it was probably overkill, because a bachelor thesis apparently doesn’t have very strict requirements (well, I’ll see about that when I get my feedback..).
  It, however, contains a few nice chapters about editing your text and improving its readability, and the punctuation and spelling chapters are nice, too.
• Oxford Guide to Effective Writing and Speaking
  I’ve only read this book in parts but it’s not bad. It contains a useful introduction to English grammar, if you want to refresh that knowledge.
• Oxford Guide to Plain English
  This book is simply awesome. Plain English refers to writing English in a simple and easily understood way. This book describes what makes a text ‘plain’ and easy to read and how to transform your texts to improve readability. It contains lots and lots of examples of complicated texts an shows how easy it is to improve them with few changes.
  The book itself is a very nice read and in parts even funny. The author clearly knows what he is teaching and it helped me a lot while writing my bachelor thesis.

Writing the Thesis

I had two months for the implementation of the project and for writing the thesis. The plan was to implement everything in August and write everything in September and be done at the beginning of October (before my birthday).

Instead last week I ended up being in crunch mode working 15 hours on it every day

The implementation went mostly as planned. I found a few driver bugs though, bought gDEBugger for debugging shader issues and found some bugs in it, too. I think I reported 5-7 bugs in gDEBugger’s support forum in a matter of days and still have to write/extend a few reports.

I wrote my thesis in LaTeX and used the very good Texmaker as editor. It supports multiple file projects and allows you to select a main file (usually latex is called with the file that is currently being edited).

jEdit also supports LaTeX editing through a plugin: LaTeXTools. It isn’t working as well as Texmaker though, but it has generally more text editing options and supports directory searches and regexp which is useful for a multi-file project.

I used subversion for version management, which proved useful at times, even though TortoiseSVN’s difference viewer doesn’t support line wrapping, which sucks a bit because I always write long blocks of text in Texmaker and it made diff’ing difficult.

For creating vector graphics, a very cool LaTeX package exists. It’s called TikZ (“Tikz ist kein Zeichenprogramm”), and it allows you to create illustrations the LaTeX way: by coding them.
See http://www.texample.net/tikz/examples/ for some neat looking examples.

I really wanted to use it to create my illustrations, but due to time constraints I couldn’t read the whole manual (it’s huge!) and I think even then it would have been too difficult.
You see, it suffers from the same problem TeX and LaTeX suffer from in general. It’s easy to write something that looks okay, but as soon as you want to tweak something to look exactly the way you imagine it and it is not a standard option, you end up reading weird package code and wishing you had a Phd in TeX editing.

TikZ has exactly the same problem. I’ve understood the tutorials and the manual well enough, but I wanted to create class diagrams with it. I got lost quickly and the 500 page manual didn’t offer a straight-forward way either.

In the end I installed the latest version of Inkscape and created all my illustrations with it. Well, actually I always tried to create them with TikZ first, got frustrated after losing an hour or two, and spent another hour creating them in Inkscape.

While Inkscape makes it harder to change an illustration later on and there is no way to layout diagrams automatically, you can still become quite fast with it after learning a few hotkeys.

I wanted to use Eclipse and Omondo’s UML plugin to create some diagrams of a Java subproject and it failed horribly..

Having to wait 20 minutes, while it hogs your computer at 100% CPU usage and 400 MB memory usage, to create a UML model of a 5 classes project is quite unacceptable!

Starting Eclipse later crashed it every time, too, by the way. I had to uninstall the damned plugin for Eclipse to start at all again.

In the end I recreated the classes in C++ and used Visual Studio’s class diagram viewer to display the classes. You can then print the diagram to PDF and edit it some more in Inkscape, which supports importing single-page PDFs.

I hope I’ll find time to write about game development related topics again in the next weeks. There are a few things I want to work on, but sadly university starts on Monday again and it will probably use up most of my time.

Cheers,
Andreas

To sum it up, it is somewhat awkward, at least if you use the IDE itself. FlashDevelop still is as nice as ever, but you can quickly develop games nonetheless. I prefer Torque Game Builder though in retrospect.

Before I continue talking about the development itself, let’s take a look at the actual game. Sploidz was the first game I wrote using Torque Game Builder for Joshua Dallman, and since I still had all the assets in my subversion repository, it was an easy decision to try and port this game. If you want to play it, you can download it for free here.
I haven’t ported everything: I’ve just rewritten the main characteristic features that make up Sploidz’s code in ActionScript.

Without further ado´ here is the game:

Click to open Sploidz in its own window

Because the art is still copyrighted and I haven’t heard back from Joshua yet ´, I decided to create a free version that only uses “coder art” – in this hand-drawn coder art

Some´ have said that this version looks cuter, decide for yourself:

Click to open SploidzCC in its own window

Below you’ll find a description of the development and at least one helpful trick and most importantly a link to the source code of the “copyright-free” version.

Because the orginal version is way too difficult to be really fun, I actually sat down one more time and added code to make the platform slower if you’re in danger of losing (up to 3 times slower):

Click to open SploidzMoreFun in its own window

Development

I think I spent less than 20 hours on the project. It’s hard to say because I worked on it on three different days, but only probably less than 6 hours on each.

The main problems during the development were:

• How do I get the art assets into Flash?
• How do I use the IDE and objects in a way that is helpful?

Lessons learned:

Even though the project isn’t that big, it didn’t take long for annoying bugs to appear – mainly in the matching code, because it’s somewhat asynchronous and you have to make sure that an item doesn’t get removed between events, etc.
So again, I can only say that assertions and lots of debug messages are your friend and are really useful for understanding the sometimes mysterious ways of non-obvious code interaction.

Again one of the biggest headache was how to make the game a game (so you don’t always and feel some reward while playing) and this resulted in implementing the platform game element from the original Sploidz game, although I wanted to avoid that in the beginning because of the added complexity.
Someone´ pointed out though, that if you have 8 columns and only 5 different item types, the main idea of matching items becomes trivial. It’s obvious, but I didn’t think of it while coding the proof of concept code.
Of course you have to somewhat tune the speed and animation durations of everything to make it playable. I think the game is really hard at the moment, but that’s better than too easy and I especially added the “survival timer” in the upper right panel to allow for some competition and personal best times.
I might change the platform code at some point to be more player-friendly, but I have more pressing projects to do at the moment: my Bachelor Thesis… /o\.
As said above, I actually sat down and added a time scaler to the platform. The code is quite simple but helps the game a bit (I managed to survive 2 minutes and it was more challenging and less depressing to play the game ^ ^). The code is quite simple:

public function getPlatformTimeScale():Number {
	var maxRow:int = 0;
	for ( var column:int = 0 ; column < Grid.numColumns ; column++ ) {
		var firstEmptyRow:int = grid.getFirstEmptyCellRow( column );
		if ( firstEmptyRow > maxRow ) {
			maxRow = firstEmptyRow;
		}
	}

	const minScale:Number = 1.0;
	const maxScale:Number = 3.0;
	var scale:Number = minScale + (maxScale - minScale) * Math.pow( maxRow / (Grid.numRows - 1), 8 );
	trace( "Using platform scale: " + scale );
	return scale;
}

As you see, it uses a power function to make the platform slower only if really few empty rows are left.

Interesting things to know

• If you want to important a sequence of images (say you have an animation stored as picture frames diamond_black00.png to diamond_black15.png, only select the first image when “importing to stage” in Flash, otherwise you won’t get the dialog asking you whether you want to import an image sequence as animation.
  (Cost me a few hours of searching to find this out.)
• If you have animations that stores multiple frames in one image, you’ll have to split the images up into the respective frames. To do this in Photoshop make use of “guides” and slicing and notice the “Slices from Guides” button that is offered. It’s really helpful.
  You can also store the creation of the guides and the slicing as action/macro and reuse it which also saves some time.
• If you ever get the error “type was not defined or was not a compile-time constant”, you might have a symbol instance that has the same name and class name. Flash freaks out for some reason and displays this weird error message.

For added fanciness, I’ve also included two older builds that show the evolution of the game code.

Note: There are bugs in these builds, so they are really just meant to show the progress on the first and second day.

Click to open Sploidz0810 in its own window

Click to open Sploidz0813 in its own window

Fun note: I implemented most of the fancy features (combo matches, the score bubbles, the platform) today in a few hours (a lot less than expected). I think ActionScript is an okay language, although it lacks quite a few comfort features of regular modern programming languages (function overloading, delegate types that actually check parameter type).

Last but not least here is the link to the code: FlashySploidz Source
I release the code itself under GPL and the art under Common Creative.

Over and out,
Andreas