I'm pretty new to HTML5, and want to know if this is possible.
I want to be able to create a canvas in which I can load an image in it, and then draw on it for other people to see, and allow them to make changes to it as well.
It doesn't have to be super complicated with lots of different tools, just basic stuff. I just want to be able to change the image every now and again.
Is this possible, and if so, can someone point me towards a tutorial of some sort?
Do you already know how to do non-image collaboration?
The way you do collaborative editing of any medium is pretty much the same.
The main difference between one medium and the next is the content of the updates (DOM elements vs. paint events). The other big thing you'll run into has nothing to do with the medium, but whether you want to use AJAX or WebSockets or what have you - this is a question more about the method through which you accomplish the collaboration.
The essential concept is (from the user's perspective):
Submit my own changes
Check periodically via AJAX to see if anyone else has made changes, or use WebSockets/long polling to be notified immediately of changes from others
Update each person's view with the changes from other users
Figure out a way to resolve conflicts if two changes are incompatible, if this applies to your problem
Provide some way for users to "undo" things
Not to blow my own horn, but last year I wrote a collaborative scratch paper/brainstorming app called cortex, and I blogged about each commit and how I figured out how to do the realtime collaboration. I did it in Rails using an AJAX approach, but the concepts I used for real-time collaboration are applicable to most any app that wants to take a similar approach. This post includes a video simulating two users collaborating on the same page, and how soon/how often updates from one client are shown on the other client browswer.
cortex isn't the prettiest or most advanced thing in the world, but I think it's a good intro app to get the concepts down. It may not even be the best designed (it was my first collaboration app), but I use it nearly every day and it seems to work well enough.
I'd like to start developing a "simple" game with HTML5 and I'm quite confused by the many resources I found online. I have a solid background in development, but in completely different environments (ironically, I started programming because I wanted to become a game developer, and it's the only thing I've never done in 13 years...).
The confusion derives from the fact that, although I know JavaScript very well and I have some knowledge of HTML5, I can't figure out how to mix what I know with all this new stuff. For example, here's what I was thinking of:
The game would be an implementation of chess. I have some simple "ready made" AI algorithm that I can reuse for single player; the purpose here is to learn HTML5 game development, so this part is not very important at the moment.
I'd like build a website around the game. For this I'd use a "regular" CMS, as I know many of them already and it would be faster to put it up.
Then I'd have the game itself, which, in its "offline" version, has nothing to do with the website, as, as far as I understand, it would live in a page by itself. This is the first question: how to make the Game aware of User's session? The login would be handled by the CMS (it should be much easier this way, as User Managememt is already implemented).
As a further step, I'd like to move the AI to the server. This is the second question: how do I make the game send player's actions to the Server, and how do I get the answer back?
Later on, I'd like to bring a PVP element to the game, i.e. one-against-one multiplayer (like the good old chess). This is the third question: how to send information from a client to another, and keep the conversation going on. For this, people recommended me to have a look at Node.js, but it's one more element that I can't figure out how to "glue" to the rest.
Here's an example of a single action in a PVP session, which already gives me a headache: Player 1 sends his move to the Server (how does the game talk to Node.js?). I'd need to identify the Game Id (where and how should I store it?), and make sure the player hasn't manually modified it, so it won't interfere with someone else's game (how?).
I'm aware that the whole thing, as I wrote it, is very messy, but that's precisely how I feel at the moment. I can't figure out where to start, therefore any suggestion is extremely welcome.
Too many things and probably in the wrong order.
A lot of the issues don't seem to me to be particularly related to HTML5 in the first instance.
Start with the obvious thing - you want a single page (basically a javascript application) that plays chess, so build that. If you can't build that then the rest is substantially irrelevant, if you can build (and I don't doubt that you can) then the rest is about building on that capability.
So we get to your first question - well at the point at which you load the page you will have the session, its a web page, like any other web page, so that's how you get the session. If you're offline then you've persisted that from when you were online by whatever means - presumably local storage.
You want to move the AI to the server? Ok, so make sure that the front end user interaction talks to an "interface" to record the player moves and retrieve the AI moves. Given this separation you can replaces the AI on the client with an ajax (although I'd expect the x to be json!) call to the server with the same parameters.
This gets better, if you want to do player to player you're just talking about routing through the server from one user/player to another user/player - the front end code doesn't have to change, just what the server does at the far end of the ajax call.
But for all this, take a step back and solve the problems one at a time - if you do that you should arrive where you want to go without driving yourself nuts trying to worry about a bucket full of problems that seem scary that you can probably easily solve one at a time and I'd start by getting your game to run, all on its own, in the browser.
About question one: You could maybe give the user a signed cookie. E.g. create a cookie that contains his userid or so and the SHA2 hash of his userid plus a secret, long salt (e.g. 32 bytes salt or so).
About question two: For exchanging stuff and calling remote functions, I'd use the RPC library dnode.
About question three: Use the same thing for calling methods between clients.
Client code (just an example):
DNode.connect(function (remote) {
this.newPeer = function(peer) {
peer.sendChatMessage("Hello!");
};
});
You don't have to use game IDs if you use dnode - just hand functions to the browser that are bound to the game. If you need IDs for some reason, use a UUID module to create long, random ones - they're unguessable.
As far as I know, it's really not possible, but I just want to be sure before I'm moving to flash.
can I make an html5 game secure enough so people won't be able to change their score and other variables while playing?
thanks!
There is no "depends", the straight answer to your question is "no" and I think my fellow answerers simply muddied the waters.
You cannot trust the client. With any language, whether you're writing assembly or HTML or Flash, you cannot trust the client. No matter how much you wrap your code in obfuscation and such, it can and will be figured out (and often quicker than you might think).
This is stressed everywhere and yet people keep getting bit by it. Online games get "speedhacked" because they don't check the velocity of players, or they get item duplication because they don't verify that a player actually has an item that they're trying to do something with, or the lame little flash games get hiscore entries of 9999999 because a simple tool like Tamper Data (a Firefox add-on) is all it takes to change the score as it's sent to the server.
You can't trust the client, whether HTML5 or Flash.
If it's a single-player game, let the player cheat. That is their decision. If it's a multiplayer game, the server verifies every step of the game and anything outside of the rules is thrown out. If it's hiscores, send a replay of the game to the server and analyze it for any cheating rather than sending just a numeric score.
since your users can see all the source code this is a rather complex problem.
they can easily change any function or variable at runtime without your script ever knowing.
even if use a complicated signing function to validate the results.
and i am sorry but i don't think colins way would work either. i could just change any input to make the server do whatever i want.
maybe a constant monitoring of the score thru the server would be able to detect any impossible changes. still someone cheating in the realms of "possible" results would be uncaught.
in the end i would say u can only make it rather difficult to cheat but not impossible for someone with a little bit of skill.
don't use it for any games where u can win something by scoring the highest.
since the matter seems rather puzzling to people:
flash delivers compiled swf files, that cannot (since flash 9) be decompiled to useful.smth
so u can put a secret in there which you use to sign the score.
i.e. send the score and the md5 of score+secretkey. so the server (which also knows the key, can check it).
furthermore flash variables are not so easy to temper with (you would have to find them in ram and alter them there, which is a very complex task), while javascript vars can be easily edited using, for example, webkit developer tools
update
actually i correct myself => all swfs can be decompiled
this just leaves us with code obfuscating and "encrypting"
i guess the world is a bad place after all ;)
Depends on the way your game is coded, but if all the logic is sent to the client and only the score returned then you have no hope. Only by returning the inputs and calulating the score on the server side can you try to prevent the users submitting any score they wish.
Don't forget, by definition the user must change their score or it could never be more than 0...
One Thought!!
You may use Knockout.js to modify your score and other variables as observable properties.
The steps are:
Create ViewModal for your game
Create observable properties for all the variables (i.e score)
You need to store the score in cache so that you can access it when new score arrives.
Attach custom subscriber to these properties and write logic to check the score should be updated by a "UNIT" at a time ( by unit I mean, how you suppose to update user's score at a time). The difference between the last score and current score should not go beyond the "UNIT"
update scroe as ViewModal.Score(newScore); //this would fire an event to the subscriber of observable property.!
For a major school project I am implementing a real-time collaborative editor. For a little background, basically what this means is that two(or more) users can type into a document at the same time, and their changes are automatically propagated to one another (similar to Etherpad).
Now my problem is as follows:
I want to be able to detect what changes a user carried out onto an HTML textfield. They could:
Insert a character
Delete a character
Paste a string of characters
Cut a string of characters
I want to be able to detect which of these changes happened and then notify other clients similar to "insert character 'c' at position 2" etc.
Anyway I was hoping to get some advice on how I would go about implementing the detection of these changes?
My first attempt was to consider the carot position before and after a change occurred, but this failed miserably.
For my second attempt I was thinking about doing a diff on the entire contents of the textfields old and new value. Am I missing anything obvious with this solution? Is there something simpler?
It is a really hard work make this working today, for several reasons, but
maybe you will need to restrict only to some browsers. read: https://developer.mozilla.org/en/XUL/Attribute/oninput the alternative to "oninput" is listen to all input events (keyboard, mouse, dragdrop) I suggest to use "oninput"
html is not perfect... even html5. input and textareas supports only single-range
selections. you can solve this using designmode/contenteditable instead of
textareas/textfield
detecting offsets of what changed is a hard work: read
-- https://developer.mozilla.org/en/Document_Object_Model_%28DOM%29/window.getSelection
-- http://www.quirksmode.org/dom/range_intro.html -- http://msdn.microsoft.com/en-us/library/ms535869%28v=VS.85%29.aspx -- http://msdn.microsoft.com/en-us/library/ms535872%28v=VS.85%29.aspx
you may need a "diff" algorithm written in javascript! http://ejohn.org/projects/javascript-diff-algorithm/
one personal note: detecting words, characters changes may be totally non-sense and not useful, detect instead paragraphs changes, or in case of an excel-like worksheet, the single cell
I hope this helps
feel free to correct my English!
My pseudocode/written out response would be (if I understand your question exactly) to use jQuery to detect keyup events and then save the input to the server via ajax, then also take the response and post it back to the input. This isn't very efficient, but basically the idea is that you're constantly posting and checking what else has been posted. If you want to see what someone else is doing in real time, you can ping the server every second or so and update with the response.
All of this of course can be optimized, but it still is kind of taxing for a server. You could also see if you can implement Google Topeka Wave for your project, or get in touch with Google Topeka to see how they do it :)
Stacker Nobody asked about the most shocking thing new programmers find as they enter the field.
Very high on the list, is the impact of inheriting a codebase with which one must rapidly become acquainted. It can be quite a shock to suddenly find yourself charged with maintaining N lines of code that has been clobbered together for who knows how long, and to have a short time in which to start contributing to it.
How do you efficiently absorb all this new data? What eases this transition? Is the only real solution to have already contributed to enough open-source projects that the shock wears off?
This also applies to veteran programmers. What techniques do you use to ease the transition into a new codebase?
I added the Community-Building tag to this because I'd also like to hear some war-stories about these transitions. Feel free to share how you handled a particularly stressful learning curve.
Pencil & Notebook ( don't get distracted trying to create a unrequested solution)
Make notes as you go and take an hour every monday to read thru and arrange the notes from previous weeks
with large codebases first impressions can be deceiving and issues tend to rearrange themselves rapidly while you are familiarizing yourself.
Remember the issues from your last work environment aren't necessarily valid or germane in your new environment. Beware of preconceived notions.
The notes/observations you make will help you learn quickly what questions to ask and of whom.
Hopefully you've been gathering the names of all the official (and unofficial) stakeholders.
One of the best ways to familiarize yourself with inherited code is to get your hands dirty. Start with fixing a few simple bugs and work your way into more complex ones. That will warm you up to the code better than trying to systematically review the code.
If there's a requirements or functional specification document (which is hopefully up-to-date), you must read it.
If there's a high-level or detailed design document (which is hopefully up-to-date), you probably should read it.
Another good way is to arrange a "transfer of information" session with the people who are familiar with the code, where they provide a presentation of the high level design and also do a walk-through of important/tricky parts of the code.
Write unit tests. You'll find the warts quicker, and you'll be more confident when the time comes to change the code.
Try to understand the business logic behind the code. Once you know why the code was written in the first place and what it is supposed to do, you can start reading through it, or as someone said, prolly fixing a few bugs here and there
My steps would be:
1.) Setup a source insight( or any good source code browser you use) workspace/project with all the source, header files, in the code base. Browsly at a higher level from the top most function(main) to lowermost function. During this code browsing, keep making notes on a paper/or a word document tracing the flow of the function calls. Do not get into function implementation nitti-gritties in this step, keep that for a later iterations. In this step keep track of what arguments are passed on to functions, return values, how the arguments that are passed to functions are initialized how the value of those arguments set modified, how the return values are used ?
2.) After one iteration of step 1.) after which you have some level of code and data structures used in the code base, setup a MSVC (or any other relevant compiler project according to the programming language of the code base), compile the code, execute with a valid test case, and single step through the code again from main till the last level of function. In between the function calls keep moting the values of variables passed, returned, various code paths taken, various code paths avoided, etc.
3.) Keep repeating 1.) and 2.) in iteratively till you are comfortable up to a point that you can change some code/add some code/find a bug in exisitng code/fix the bug!
-AD
I don't know about this being "the best way", but something I did at a recent job was to write a code spider/parser (in Ruby) that went through and built a call tree (and a reverse call tree) which I could later query. This was slightly non-trivial because we had PHP which called Perl which called SQL functions/procedures. Any other code-crawling tools would help in a similar fashion (i.e. javadoc, rdoc, perldoc, Doxygen etc.).
Reading any unit tests or specs can be quite enlightening.
Documenting things helps (either for yourself, or for other teammates, current and future). Read any existing documentation.
Of course, don't underestimate the power of simply asking a fellow teammate (or your boss!) questions. Early on, I asked as often as necessary "do we have a function/script/foo that does X?"
Go over the core libraries and read the function declarations. If it's C/C++, this means only the headers. Document whatever you don't understand.
The last time I did this, one of the comments I inserted was "This class is never used".
Do try to understand the code by fixing bugs in it. Do correct or maintain documentation. Don't modify comments in the code itself, that risks introducing new bugs.
In our line of work, generally speaking we do no changes to production code without good reason. This includes cosmetic changes; even these can introduce bugs.
No matter how disgusting a section of code seems, don't be tempted to rewrite it unless you have a bugfix or other change to do. If you spot a bug (or possible bug) when reading the code trying to learn it, record the bug for later triage, but don't attempt to fix it.
Another Procedure...
After reading Andy Hunt's "Pragmatic Thinking and Learning - Refactor Your Wetware" (which doesn't address this directly), I picked up a few tips that may be worth mentioning:
Observe Behavior:
If there's a UI, all the better. Use the app and get a mental map of relationships (e.g. links, modals, etc). Look at HTTP request if it helps, but don't put too much emphasis on it -- you just want a light, friendly acquaintance with app.
Acknowledge the Folder Structure:
Once again, this is light. Just see what belongs where, and hope that the structure is semantic enough -- you can always get some top-level information from here.
Analyze Call-Stacks, Top-Down:
Go through and list on paper or some other medium, but try not to type it -- this gets different parts of your brain engaged (build it out of Legos if you have to) -- function-calls, Objects, and variables that are closest to top-level first. Look at constants and modules, make sure you don't dive into fine-grained features if you can help it.
MindMap It!:
Maybe the most important step. Create a very rough draft mapping of your current understanding of the code. Make sure you run through the mindmap quickly. This allows an even spread of different parts of your brain to (mostly R-Mode) to have a say in the map.
Create clouds, boxes, etc. Wherever you initially think they should go on the paper. Feel free to denote boxes with syntactic symbols (e.g. 'F'-Function, 'f'-closure, 'C'-Constant, 'V'-Global Var, 'v'-low-level var, etc). Use arrows: Incoming array for arguments, Outgoing for returns, or what comes more naturally to you.
Start drawing connections to denote relationships. Its ok if it looks messy - this is a first draft.
Make a quick rough revision. Its its too hard to read, do another quick organization of it, but don't do more than one revision.
Open the Debugger:
Validate or invalidate any notions you had after the mapping. Track variables, arguments, returns, etc.
Track HTTP requests etc to get an idea of where the data is coming from. Look at the headers themselves but don't dive into the details of the request body.
MindMap Again!:
Now you should have a decent idea of most of the top-level functionality.
Create a new MindMap that has anything you missed in the first one. You can take more time with this one and even add some relatively small details -- but don't be afraid of what previous notions they may conflict with.
Compare this map with your last one and eliminate any question you had before, jot down new questions, and jot down conflicting perspectives.
Revise this map if its too hazy. Revise as much as you want, but keep revisions to a minimum.
Pretend Its Not Code:
If you can put it into mechanical terms, do so. The most important part of this is to come up with a metaphor for the app's behavior and/or smaller parts of the code. Think of ridiculous things, seriously. If it was an animal, a monster, a star, a robot. What kind would it be. If it was in Star Trek, what would they use it for. Think of many things to weigh it against.
Synthesis over Analysis:
Now you want to see not 'what' but 'how'. Any low-level parts that through you for a loop could be taken out and put into a sterile environment (you control its inputs). What sort of outputs are you getting. Is the system more complex than you originally thought? Simpler? Does it need improvements?
Contribute Something, Dude!:
Write a test, fix a bug, comment it, abstract it. You should have enough ability to start making minor contributions and FAILING IS OK :)! Note on any changes you made in commits, chat, email. If you did something dastardly, you guys can catch it before it goes to production -- if something is wrong, its a great way to get a teammate to clear things up for you. Usually listening to a teammate talk will clear a lot up that made your MindMaps clash.
In a nutshell, the most important thing to do is use a top-down fashion of getting as many different parts of your brain engaged as possible. It may even help to close your laptop and face your seat out the window if possible. Studies have shown that enforcing a deadline creates a "Pressure Hangover" for ~2.5 days after the deadline, which is why deadlines are often best to have on a Friday. So, BE RELAXED, THERE'S NO TIMECRUNCH, AND NOW PROVIDE YOURSELF WITH AN ENVIRONMENT THAT'S SAFE TO FAIL IN. Most of this can be fairly rushed through until you get down to details. Make sure that you don't bypass understanding of high-level topics.
Hope this helps you as well :)
All really good answers here. Just wanted to add few more things:
One can pair architectural understanding with flash cards and re-visiting those can solidify understanding. I find questions such as "Which part of code does X functionality ?", where X could be a useful functionality in your code base.
I also like to open a buffer in emacs and start re-writing some parts of the code base that I want to familiarize myself with and add my own comments etc.
One thing vi and emacs users can do is use tags. Tags are contained in a file ( usually called TAGS ). You generate one or more tags files by a command ( etags for emacs vtags for vi ). Then we you edit source code and you see a confusing function or variable you load the tags file and it will take you to where the function is declared ( not perfect by good enough ). I've actually written some macros that let you navigate source using Alt-cursor,
sort of like popd and pushd in many flavors of UNIX.
BubbaT
The first thing I do before going down into code is to use the application (as several different users, if necessary) to understand all the functionalities and see how they connect (how information flows inside the application).
After that I examine the framework in which the application was built, so that I can make a direct relationship between all the interfaces I have just seen with some View or UI code.
Then I look at the database and any database commands handling layer (if applicable), to understand how that information (which users manipulate) is stored and how it goes to and comes from the application
Finally, after learning where data comes from and how it is displayed I look at the business logic layer to see how data gets transformed.
I believe every application architecture can de divided like this and knowning the overall function (a who is who in your application) might be beneficial before really debugging it or adding new stuff - that is, if you have enough time to do so.
And yes, it also helps a lot to talk with someone who developed the current version of the software. However, if he/she is going to leave the company soon, keep a note on his/her wish list (what they wanted to do for the project but were unable to because of budget contraints).
create documentation for each thing you figured out from the codebase.
find out how it works by exprimentation - changing a few lines here and there and see what happens.
use geany as it speeds up the searching of commonly used variables and functions in the program and adds it to autocomplete.
find out if you can contact the orignal developers of the code base, through facebook or through googling for them.
find out the original purpose of the code and see if the code still fits that purpose or should be rewritten from scratch, in fulfillment of the intended purpose.
find out what frameworks did the code use, what editors did they use to produce the code.
the easiest way to deduce how a code works is by actually replicating how a certain part would have been done by you and rechecking the code if there is such a part.
it's reverse engineering - figuring out something by just trying to reengineer the solution.
most computer programmers have experience in coding, and there are certain patterns that you could look up if that's present in the code.
there are two types of code, object oriented and structurally oriented.
if you know how to do both, you're good to go, but if you aren't familiar with one or the other, you'd have to relearn how to program in that fashion to understand why it was coded that way.
in objected oriented code, you can easily create diagrams documenting the behaviors and methods of each object class.
if it's structurally oriented, meaning by function, create a functions list documenting what each function does and where it appears in the code..
i haven't done either of the above myself, as i'm a web developer it is relatively easy to figure out starting from index.php to the rest of the other pages how something works.
goodluck.