I was wondering which heuristic could fit better in the following puzzle. This puzzle comes from the game "Professor Layton" and I was trying several popular heuristic like A*, Manhattan, Euclidean... and no one convince me because there are obstacles.
The problem consists in bring the ball (the red circle) to the goal (the green dotted square). Each piece can make one movement. I hear any suggest to help me solving this problem.
The problem image:
I have tried as I said before, several algorithms that could solve the problem but anyone is really useful.
Related
Yesterday I came up with a question that I have no answer for it.
We have a random sized rectangle and we also have some circles with different radius, which we got limited amount of each of those circles. Each circle has a specified cost. We wanted to completely fill our rectangle with those circles, approaching the smallest cost.
Now I wanted to solve this problem with genetic algorithm, but I won't found any article in the web, which is somehow the same with my problem.
Does anyone has any idea?
Your problem is related to the Knapsack problem: Out of a set of N items with weights W and values V you want to select that group of items that have maximal value, but the sum of their weights remains lower than some bound.
Your problem however is more complex, since the evaluation of the weight-constraint is not a simple addition, but depends on the arrangement of the circles. I think that this constitutes another NP-hard problem to solve. You will have to find some quick approximation on that constraint that tell you if it's possible (and which sometimes may tell you it's not possible, even though it would be).
The arrangement of objects inside a container can be described as a packing problem. You may want to look at circle packing and related literature. A simple relaxation could also be based on rectangles. There are quick methods for rectangle packing which you can use if you treat your circles as rectangles. If your circles are of highly different size, however this may be a bad relaxation.
The definition of rigid body in Box2d is
A chunk of matter that is so strong
that the distance between any two bits
of matter on the chunk is completely
constant.
And this is exactly what i don't want as i would like to make 2D (maybe 3D eventually), elastic, deformable, breakable, and even sticky bodies.
What I'm hoping to get out of this community are resources that teach me the math behind how objects bend, break and interact. I don't care about the molecular or chemical properties of these objects, and often this is all I find when I try to search for how to calculate what a piece of wood, metal, rubber, goo, liquid, organic material, etc. might look like after a force is applied to it.
Also, I'm a very visual person, so diagrams and such are EXTREMELY HELPFUL for me.
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Ignore these questions, they're old, and I'm only keeping them here for contextual purposes
1.Are there any simple 2D soft-body physics engines out there like this?
preferably free or opensource?
2.If not would it be possible to make my own without spending years on it?
3.Could i use existing engines like bullet and box2d as a start and simply transform their code, or would this just lead to more problems later, considering my 1 year of programming experience and bullet being 3D?
4.Finally, if i were to transform another library, would it be the best change box2D's already 2d code, Bullet's already soft code, or mixing both's source code?
Thanks!
(1) Both Bullet and PhysX have support for deformable objects in some capacity. Bullet is open source and PhysX is free to use. They both have ports for windows, mac, linux and all the major consoles.
(2) You could hack something together if you really know what you are doing, and it might even work. However, there will probably be bugs unless you have a damn good understanding of how Box2D's sequential impulse constraint solver works and what types of measures are going to be necessary to keep your system stable. That said, there are many ways to get deformable objects working with minimal fuss within a game-like environment. The first option is to take a second (or higher) order approximation of the deformation. This lets you deal with deformations in much the same way as you deal with rigid motions, only now you have a few extra degrees of freedom. See for example the following paper:
http://www.matthiasmueller.info/publications/MeshlessDeformations_SIG05.pdf
A second method is pressure soft bodies, which basically model the body as a set of particles with some distance constraints and pressure forces. This is what both PhysX and Bullet do, and it is a pretty standard technique by now (for example, Gish used it):
http://citeseerx.ist.psu.edu%2Fviewdoc%2Fdownload%3Fdoi%3D10.1.1.4.2828%26rep%3Drep1%26type%3Dpdf
If you google around, you can find lots of tutorials on implementing it, but I can't vouch for their quality. Finally, there has been a more recent push to trying to do deformable objects the `right' way using realistic elastic models and finite element type approaches. This is still an area of active research, so it is not for the faint of heart. For example, you could look at any number of the papers in this year's SIGGRAPH proceedings:
http://kesen.realtimerendering.com/sig2011.html
(3) Probably not. Though there are certain 2D style games that can work with a 3D physics engine (for example top down type games) for special effects.
(4) Based on what I just said, you should probably know the answer by now. If you are the adventurous sort and got some time to kill and the will to learn, then I say go for it! Of course it will be hard at first, but like anything it gets easier over time. Plus, learning new stuff is lots of fun!
On the other hand, if you just want results now, then don't do it. It will take a lot of time, and you will probably fail (a lot). If you just want to make games, then stick to the existing libraries and build on whatever abstractions it provides you.
Quick and partial answer:
rigid body are easy to model due to their property (you can use physic tools, like "Torseur+ (link on french on wikipedia, english equivalent points to screw theory) to modelate forces applying at any point in your element.
in comparison, non-solid elements move from almost solid (think very hard rubber : it can move but is almost solid) to almost liquid (think very soft ruber, latex). Meaning that dynamical properties applying to that knd of objects are much complex and depend of the nature of the object
Take the example of a spring : it's easy to model independantly (f=k.x), but creating a generic tool able to model that specific case is a nightmare (especially if you think of corner cases : extension is not infinite, compression reaches a lower point, material is non linear...)
as far as I know, when dealing with "elastic" materials, people do their own modelisation for their own purpose (a generic one does not exist)
now the answers:
Probably not, not that I know at least
not easily, see previously why
Unless you got high level background in elastic materials, I fear it's gonna be painful
Hope this helped
Some specific cases such as deformable balls can be simulated pretty well using spring-joint bodies:
Here is an implementation example with cocos2d: http://2sa-studio.blogspot.com/2014/05/soft-bodies-with-cocos2d-v3.html
Depending on the complexity of the deformable objects that you need, you might be able to emulate them using box2d, constraining rigid bodies with joints or springs. I did it in the past using a box2d clone for xna (farseer) and it worked nicely. Hope this helps.
The physics of your question breaks down into two different topics:
Inelastic Collisions: The math here is easy, and you could write a pretty decent library yourself without too much work for 2D points/balls. (And with more work, you could learn the physics for extended bodies.)
Materials Bending and Breaking: This will be hard. In general, you will have to model many of the topics in Mechanical Engineering:
Continuum Mechanics
Structural Analysis
Failure Analysis
Stress Analysis
Strain Analysis
I am not being glib. Modeling the bending and breaking of materials is, in general, a very detailed and varied topic. It will take a long time. And the only way to succeed will be to understand the science well enough that you can make clever shortcuts in limiting the scope of the science you need to model in your game.
However, the other half of your problem (modeling Inelastic Collisions) is a much more achievable goal.
Good luck!
I'm trying to develop an app which allows you to walk around, and where you walked will be drawn on a map. I have this all working fine, but I'm finding that even with a reasonably accurate GPS location the points still jump around a bit. When drawn on a map this has the effect of creating a squiggly or zig-zag line.
I'm looking for suggestions/strategies on how to smooth the data, so that the line drawn on the map is more of a smooth best fit, rather than an accurate point to point drawing.
There are many different types of smoothing algorithms you could apply to the data (for a few starting points, see this Wikipedia article). The only way to know for sure which is/are suitable for your application is to implement and test them.
Simple or weighted moving averages are fairly common (taking the last n samples and averaging them), but have the problem of lagging behind the data. A common one for filtering signal noise is a high-pass filter, which attenuates small (noisy) movements while passing through larger ones. Apple has some code for this in their AccelerometerGraph sample.
I'd suggest trying those out first as they're easy to implement, before looking at the move complex ones.
I haven't taken any advanced math courses or anything (I'm still in high school) and I just don't really understand all the triangle collision systems online.
I have two triangular objects in a 2D space. How should I write Obj-C code so that a collision/intersection between the two can be detected? I'm stumped.
Perhaps one of these techniques will help:
http://www.blackpawn.com/texts/pointinpoly/default.html
Basically, to simplify things you could start by just trying to figure out if each of the three points of a triangle is inside the other one - since having a corner from one or the other enter the other one is the only way they can be overlapping.
There are lots of non-image-based CAPTCHA ideas floating around. But what about the old-fashioned way?
What are the elements of a good image CAPTCHA? What visual elements are hard for computers, but easier for humans? What about mistakes, elements that are easier for computers than they are for humans? What are good techniques for increasing the speed of a CAPTCHA generator?
Here's an example of a CAPCHA I've been working on. It generates the functions for two sine waves, then stretches a text between them. It lays that over a background drawn from a pool of images.
How could this be improved? (Specifically, I'm using PHP GD.) Things that come to mind are:
Change the color of the text, possibly making it multicolored.
Add "scratches" or marks that mildly obscure the text.
Add to the distortion so that it's affected by sine waves horizontally as well.
What goes into a superb image CAPTCHA?
Edit:
I know that there are some very worthy third-party CAPTCHA resources. I'm looking for attributes that make them good. I'd like to use my own CAPTCHAs, just for the purpose of self-improvement. So, you can talk about reCAPTCHA, but it's not exactly what I'm looking for.
Also, it has been brought up that not only the image, but also the experience matters, so feel free to comment on that.
Make each letter/number out of a pattern, I.E. unconnected dots. Meaning the computer has no way of knowing that a dot is part of a letter other than pattern recognition (which they don't have yet.) Then the usual distortions and random lines.
How you do this is the challenge.
EDIT: Also, bonus points for patterns of different shapes, and try alpha transparency on the characters (on the edges or the whole character), so they merge with the background.
Make letters difficult to separate. Use handwriting-like font or add lines that join letters. Decrease and randomize spacing between letters.
Add wave distortion in other axis too. Distortion in one axis only can be relatively easily analyzed and reversed.
Don't bother with color background at all. It's super-easy to automatically filter black from other colors. Your background hinders only humans.
Don't add scratches or other noise unless it has the same thickness as letters. Noise-removal algorithms can easily remove things that are thinner than letters.
What if the color of the letters faded into other colors... for instance the 5 can start off as yellow on top and fade into blue or something. The colors chosen should be random.
With the multicolored background it might make it hard for the computer to pickup where the background ends and the character begins.. and hopefully it would not be too difficult for the human to actually pick up the pattern.
Instead of generating captcha you can create a captcha table in your database and you yourself create the table by search on google for good captcha images.
So no need to worry "Will this generation method work?"
I really hate CAPTCHA on sites, they just annoy me, but if you want to try and make a robust one try the following:
Ability to get a new image without submitting
Spoken version for the visually impaired
Non-uniform characters
I've used Recaptcha on a few sites, it's a nice and robust solution.
Or if you want to be really funky about it check out this: http://research.microsoft.com/asirra/
Algorithms that try to break captcha are pattern matchers that work by a few different ways: scaling and skewing the symbols that they already know about, finding and tracing edges, and counting interior holes to help. If you can break the letter up into pieces, vary the letter quality, or add strong lines or “scratches” along the letters these techniques will help. However all of this is fairly moot considering we have recaptcha for this purpose and it’s a wonderful third party app for this. Additionally captcha will help the security of your site, but will not stop those who are truly enticed.
I like the idea of KittenAuth and Microsoft's Asirra project. The idea is that, while OCR will eventually evolve to break your traditional captcha, the ability to distinguish a kitten from a dog is many orders of magnitude more complex a problem, while absolutely trivial for humans.
This solution, while probably the sexiest captcha idea ever, has the limitation of not being easily portable to hearing-impaired methods.
What about shearing and shuffling bands to mangle display and mouse-only input?
Start by taking your sine-wave morphed text, divide into horizontal bands or maybe even a grid.
That makes optical recognition harder and might allow you to avoid the kind of nasty background games that make some captchas hard for humans.
For a site where you can rely on local drag in the browser, instead of typing in an entry use shuffling requiring the user to re-order pieces (just in sloppy order, not like one of those puzzles). Or, if you wanted to use clicks alone, the classic sliding tile puzzle.
Note, I've run into a captcha where you had to identify which of N cartoons had an animal in them which succeeded in blocking me!
Wellington Grey sums up the AI CAPTCHA race nicely.
You could add a random array of fonts so that GD renders each character using a different one.
Be wary of suggestions of ReCaptcha. I have submitted incorrect input into it a couple few dozen times, and have had success each time. Several of those times I have submitted incorrect input for both words rather than just the most obscured word; the success rate, as I said, has been 100%.
I also think that image-based CAPTCHAs are user-hostile and should be avoided wherever possible. The advantage of text-based solutions is that you can tailor them to your site's audience, adding a level of obscurity that may trip up machines as they become more savvy with text-based solutions.
At the very least, don't use this all the time:
(source: codinghorror.com)