Develop Reference

A maze game for touch-devices

Purpose: I want to create a game like this one
Problem: How to make it so that when dragging an item it does not go beyond the borders of the cell? I can do it like this, but you can easily control it from the keyboard, but somehow I’ll find it difficult to work with dragging. In other words, it is required that dragging an item is only possible along a particular path (as in the example of the game above)
Any thoughts? Any options and solutions are welcome. Thanks!

Judging by the example you gave you can do this by placing the walls around the item. Whenever the system detects collision with the walls movement of the item will stop. I have mostly used this functionality with Unity Engine so i am afraid i can't provide you with specific codes.
Check this video: https://www.youtube.com/watch?v=hNV-xEMALr8
I think you will be able to figure this out after watching it.

logic to see if board game pieces have been captured (go)

im developing an online version of the board game go, a japanese game which players take it in turns to place their stone on the grid. When one players stones are surrounded by their opponents, they are destroyed.
This is the logic i cant get my head around how i would program. So far ive made the 2 player grid where all the stones placment are stored in an array. I will include a picture which will make it much clearer here
So as you can see, the grid shows that black has 2 white stones surrounded in which case they should be destoryed, note that it can be any number of surrounded stones but in this case its 2.
To the right you can also see the array of stones which i will use to check if a player has been surrounded. I tried to make some pysudo code but it was becoming a mess and way over complicated, is this task really that complicated? any adivice or logic behind how i would do this would be appriated so if anyone online has done something similar that would be good too. Im not even sure making an array like i have done is the best way in the end so if theres a better way please let me know

I would recommend a different data model--essentially a two-dimensional array, holding values of 0, +1, and -1, for empty, black, and white respectively. For purposes of your algorithm, maintain a parallel array of booleans for "has liberty".
Your algorithm will need to scan the board multiple times. Prior to the scan, set the "has liberty" flag for a location to false if and only if the location is occupied. On each scan, find all the cells with "has liberty" of true and mark the cell to the left, right, top, and bottom as "has liberty"; if the location is occupied, restrict this marking to adjacent locations of the same color. When nothing changes on the board after a scan, you are done. At that point, all the stones with "has liberty" remaining false are captured and should be removed.
This is a simple, inefficient algorithm. Go engines such as GNU go have much more sophisticated algorithms that involve keeping track of "chains" or "groups" of connected stones, with their number of liberties, and then update those as stones are played. If you are planning to write a go-playing program, you will be doing this calculation thousands or millions of times as you read out different sequences, so that kind of optimization will become crucial.
Note that you will need to do special casing for the situation known as "ko" and similar situations where a stone is played in a seemingly "captured" position but survives because it itself takes other stones. . If you simply place the stone taking the ko on the board, and run the above algorithm, then both the stone being taken and the stone just played will be considered to be captured, which is wrong. Therefore, you need a board-level variable for most recent stone, and consider that stone to always be in the "has liberty" state, with appropriate logic to handle illegal moves.

A general rough outline for the algorithm:
Determine all the spots adjacent to your white pieces (let's use white here for clarity):
create two buckets (arrays): white pieces to check, adjacent spots
take any white piece, put it into the white-pieces bucket
for all the white pieces in your white-pieces bucket, determine their adjacent spots (up, down, left, right)
if there's no white piece on that spot, put the spot into the adjacent-spots bucket
if there's a white piece on that spot, put it into the white-pieces bucket
repeat this process until your white-pieces bucket is empty (you have found all the white pieces in a group)
(make sure you deduplicate your buckets in the process so you're not running around in circles)
Check whether all of the adjacent spots are covered in black pieces.
There's a ton of optimisation that can be done that would make this algorithm much more complicated, and a professional Go program is much more complex than this, but it gets you started.

How do I make a game engine in a game? (with HTML5 and Javascript)

I want to make an operating system for the character in my HTML5/Javascript game, and I don't want to use libraries.
I found something about controlling my character with my mouse and arrows, and it worked for me, but I want to go deeper into this subject.
SO: the thing is:
I want to control my character smoothly, en when I jump, it automatically turn down, etc.
Here is an example of what I mean. When you go to this webpage, there is a little guy all the way left of the screen. You can walk with the W/A/S/D keys with this character through the website. How do I make such a little guy?
I hope this was enough (maybe a lot) information to describe my problem. Maybe there are some nice tutorials about this subject.

asynchronous / variable framerate in javascript game

This may be a stupid/previously answered question, but it is something that has been stumping me and my friends for a little while, and I have been unable to find a good answer.
Right now, i make all my JS Canvas games run in ticks. For example:
function tick(){
//calculate character position
//clear canvas
//draw sprites to canvas
if(gameOn == true)
t = setTimeout(tick(), timeout)
}
This works fine for CPU-cheep games on high-end systems, but when i try to draw a little more every tick, it starts to run in slow motion. So my question is, how can i keep the x,y position and hit-detection calculations going at full speed while allowing a variable framerate?
Side Note: I have tried to use the requestAnimationFrame API, but to be honest it was a little confusing (not all that many good tutorials on it) and, while it might speed up your processing, it doesn't entirely fix the problem.
Thanks guys -- any help is appreciated.

RequestAnimationFrame makes a big difference. It's probably the solution to your problem. There are two more things you could do: set up a second tick system which handles the model side of it, e.g. hit detection. A good example of this is how PhysiJS does it. It goes one step further, and uses a feature of some new browsers called a web worker. It allows you to utilise a second CPU core. John Resig has a good tutorial. But be warned, it's complicated, is not very well supported (and hence buggy, it tends to crash a lot).
Really, request animation frame is very simple, it's just a couple of lines which once you've set up you can forget about it. It shouldn't change any of your existing code. It is a bit of a challenge to understand what the code does but you can pretty much cut-and-replace your setTimeout code for the examples out there. If you ask me, setTimeout is just as complicated! They do virtually the same thing, except setTimeout has a delay time, whereas requestAnimationFrame doesn't - it just calls your function when it's ready, rather than after a set period of time.

You're not actually using the ticks. What's hapenning is that you are repeatedly calling tick() over and over and over again. You need to remove the () and just leave setTimeout(tick,timeout); Personally I like to use arguments.callee to explicitly state that a function calls itself (and thereby removing the dependency of knowing the function name).
With that being said, what I like to do when implementing a variable frame rate is to simplify the underlying engine as much as possible. For instance, to make a ball bounce against a wall, I check if the line from the ball's previous position to the next one hits the wall and, if so, when.
That being said you need to be careful because some browsers halt all JavaScript execution when a contaxt menu (or any other menu) is opened, so you could end up with a gap of several seconds or even minutes between two "frames". Personally I think frame-based timing is the way to go in most cases.

As Kolink mentioned. The setTimeout looks like a bug. Assuming it's only a typo and not actually a bug I'd say that it is unlikely that it's the animation itself (that is to say, DOM updates) that's really slowing down your code.
How much is a little more? I've animated hundreds of elements on screen at once with good results on IE7 in VMWare on a 1.2GHz Atom netbook (slowest browser I have on the slowest machine I have, the VMWare is because I use Linux).
In my experience, hit detection if not done properly causes the most slowdown when the number of elements you're animating increases. That's because a naive implementation is essentially exponential (it will try to do n^n compares). The way around this is to filter out the comparisons to avoid unnecessary comparisons.
One of the most common ways of doing this in game engines (regardless of language) is to segment your world map into a larger set of grids. Then you only do hit detection of items in the same grid (and adjacent grids if you want to be more accurate). This greatly reduces the number of comparisons you need to make especially if you have lots of characters.

Structuring an HTML5 Canvas/JS Game

I'm new to HTML5/Canvas/Game programming, but have been tinkering around with it after reading a couple of books. I THINK I have a fairly good idea of how things work out. This question asks several smaller questions, but in general is basically a "structural approach" question. I'm not expecting verbose responses, but hopefully small pointers here and there :) Here is a link to a non-scrolling, and currently rather boring Super Mario World.
Super Mario World Test
NOTE: Controls are Left/Right and Spacebar to jump. This is only setup for Firefox right now as I'm just learning.
Did I Do Something Wrong at This Point?
Currently I've just focused on how Mario runs and jumps, and think that I've gotten it down fairly okay. The coin box doesn't do anything and the background is just an image loaded in for looks. Here's my approach, please let me know if there is anything entirely wrong with this:
Allows Mario to jump by enacting on 2 Y velocities (Gravity and Jump variables)
Allows Mario to run by enacting on 1 velocity (Left or Right "Friction" + Acceleration)
Sprites are used and positioned according to keypress/keydown
I'm not sure if this is right, but I'm using a constructor function to build an object, then inside the main animation loop I'm calling the prototype.draw function for that object to update all variables and redraw the object.
I'm clearing the entire canvas each Frame
Should I be splitting this into more than just a draw function, like Mario.move()?
I've setup a GroundLevel and a JumpLevel variable to create 2 planes of gameplay. The JumpLevel is setup to allow for controlling how high Mario can jump on the fly. The 2 places would allow for the ground to rise like a hill - keeping the point at which Gravity overrules Mario's jumping force at the same distance from the ground.
For clarity sake, everything is separated into different JS files, but would obviously consolidate.
Moving Forward:
Now that I've finished setting up how Mario moves around (I think there are a couple other minor things I might do like mushroom up/down and shooting fireballs). I think I can figure that out, but I'm really lost when it comes to visualizing the following and how HTML5/Canvas can handle this easily:
Scrolling background (I've tried setting up Ground Tiles and using Screen Wrapping, but that seems to cause a lot of uneven issues since I was moving the tiles in the opposite direction. Unfortunately, since I'm trying to account for acceleration, this threw off the count and was causing gaps in the ground. I ditched this idea. Would a DIV beneath the canvas with a large background image be the best solution?
Enemies: Would I create enemies the same way and run a loop for collision detection on every enemy during each frame?
Background Boxes: I'm trying to allow Mario to stand on the boxes in the background, but am unsure how to approach this. I currently have boundaries setup for Mario to stay on the canvas, do I continue to expand these conditions to setup different boundaries based on the boxes? I can see that having several boxes on the screen and doing it this way would get kind of crazy, especially if I would be doing the same hit testing for enemies? I know I'm missing something here....
Level Movement: This is somewhat related. When the Right key is pressed, basically everything in the level needs to move to the left. Would I need to track out all positions of everything that could touch Mario (boxes for him to stand on and enemies for him to collide with) during every animation frame? This seems like it would get kind of inefficient?
Thanks to all! I'll keep this updated with results/solutions :)

Wow, okay. I really like your question because you've obviously done a lot of thinking on this, but partially because of that it's incredibly broad and conversational. You'd do better to find a forum to ask this question.
...That being said, I'm gonna answer the handful of points I'm qualified to, in no particular order. :)
Level Movement: That's a weird (read: inefficient) way to do it. I wouldn't do any calculations based on onscreen positions: track a canonical, camera-agnostic set of coordinates for everything in your level and update the visuals to match. This will stop you from running into weird niggling problems where framerate impacts what you can and can't walk through, or causing slower computers to let Mario run through enemies without being damaged sometimes. Tracking positions this way will incidentally fix a lot of your other problems.
You should absolutely be splitting this into multiple functions. Having movement code and rendering code in the same place is going to screw you, particularly by interacting malignantly with your update/refresh rate. It's going to essentially mean that every time the player does a tricky jump the game does more updates than usual which will make animation/hit detection/etc much less likely to be even.
Enemies: I'd suggest rolling this in with everything else. Do one hit-detection pass against everything, and if you hit something check to see what it was. You could try to optimize this by only checking any given entity against objects within 100 pixels of itself, but if you do it this way you'll need to run separate collision detection events for every enemy. Letting the enemies clip through each other would be computationally cheaper.
Edit: I'd like to clarify about my first point on 'level movement.' Essentially, what you don't want to do is move every entity onscreen every time the camera does, or to store all entity locations as offsets from the camera location (in which case you're still effectively having to move everything, every time the camera moves.)
Your ideal approach is to store your enemy, block, terrain locations with X/Y coordinates that are offset from the absolute top-left of the level (at the very beginning.) In order to render a frame, you'd do essentially this: (pseudocode because we're talking about a hypothetical level format!)
function GetVisible(x,width,level_entities_array) {
for (i = 0; i < count(level_array); i++){
if (level_entities_array[i][x] > x && level_entities_array[i][x] < x+width) {
visible_elements[] = level_entities_array[i][x];
}
}
return visible_elements;
}
Boom, you've got everything that should be inside the window. Now you subtract the camera's x offset from the entity's x location and ZAP, you've got its position on the canvas. Pose as a team, 'cause things just got real.
You'll note that I'm not bothering to cull on the Y axis. This can be rectified by extrapolation, which I'm guessing you can handle because you've made it this far. This will be necessary if you want to do any Mario-style vertical exploration.
Yes, I know my pseudocode looks like C# and JavaScript's unholy lovechild. I'm sorry, that's just how I roll at 11:30 at night. ;)