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• SQL SERVER – Simple Explanation and Puzzle with SOUNDEX Function and DIFFERENCE Function

  - by pinaldave

  Earlier this week I asked a question where I asked how to Swap Values of the column without using CASE Statement. Read here: A Puzzle – Swap Value of Column Without Case Statement,there were more than 50 solutions proposed in the comment. There were many creative solutions. I have mentioned my personal favorite (different ones) here: Solution of Puzzle – Swap Value of Column Without Case Statement. However, I received lots of questions regarding one of the Solution by SIJIN KUMAR V P. He has used the function SOUNDEX in his solution. The request was to explain how SOUNDEX and DIFFERENCE works. Well, there are pretty decent documentations provided over here SOUNDEX function and DIFFERENCE over on MSDN and if I attempt to explain this function I will end up writing the same details which are available on MSDN. Instead of writing theory, we will try to learn this function by using a couple of simple puzzles. You try to solve the puzzles using the MSDN and see if you can learn something very quickly. In simple words - SOUNDEX converts an alphanumeric string to a four-character code to find similar-sounding words or names. The first character of the code is the first character of character_expression and the second through fourth characters of the code are numbers that represent the letters in the expression. Vowels incharacter_expression are ignored unless they are the first letter of the string. DIFFERENCE function returns an integer value. The  integer returned is the number of characters in the SOUNDEX values that are the same. The return value ranges from 0 through 4: 0 indicates weak or no similarity, and 4 indicates strong similarity or the same values. Learning Puzzle 1: Now let us run following four queries and observe its output. SELECT SOUNDEX('SQLAuthority') SdxValue SELECT SOUNDEX('SLTR') SdxValue SELECT SOUNDEX('SaLaTaRa') SdxValue SELECT SOUNDEX('SaLaTaRaM') SdxValue When you look at the result set all the four values are same. The reason for all the values to be same is as for SQL Server SOUNDEX function all the four strings are similarly sounding string. Learning Puzzle 2: Now let us run following five queries and observe its output. SELECT DIFFERENCE (SOUNDEX('SLTR'),SOUNDEX('SQLAuthority')) SELECT DIFFERENCE (SOUNDEX('TH'),SOUNDEX('SQLAuthority')) SELECT DIFFERENCE ('SQLAuthority',SOUNDEX('SQLAuthority')) SELECT DIFFERENCE ('SLTR',SOUNDEX('SQLAuthority')) SELECT DIFFERENCE ('SLTR','SQLAuthority') When you look at the result set you will get the result in the ranges from 1 to 4. Here is how it works if your result is 0 which means absolutely not relevant to each other and if your result is 1 which means the results are relevant to each other. Have you ever used above two functions in your business need or on production server? If yes, would you please leave a comment with use cases. I believe it will be beneficial to everyone. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Multiple Key Presses in XNA?

  - by Bryan Harrington

  I'm actually trying to do something fairly simple. I cannot get multiple key presses to work in XNA. I've tried the following pieces of code. else if (keyboardState.IsKeyDown(Keys.Down) && (keyboardState.IsKeyDown(Keys.Left))) { //Move Character South-West } and I tried. else if (keyboardState.IsKeyDown(Keys.Down)) { if (keyboardState.IsKeyDown(Keys.Left)) { //Move Character South-West } } Neither worked for me. Single presses work just fine. Any thoughts?

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• 2D Tile-Based Concept Art App

  - by ashes999

  I'm making a bunch of 2D games (now and in the near future) that use a 2D, RPG-like interface. I would like to be able to quickly paint tiles down and drop character sprites to create concept art. Sure, I could do it in GIMP or Photoshop. But that would require manually adding each tile, layering on more tiles, cutting and pasting particular character sprites, etc. and I really don't need that level of granularity; I need a quick and fast way to churn out concept art. Is there a tool that I can use for this? Perhaps some sort of 2D tile editor which lets me draw sprites and tiles given that I can provide the graphics files.

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• Website Access...DNS, ISP, issue?

  - by sublet

  This isn't so much a code issue as it might be an issue with my ISP. For some reason when I visit a site very often, like one I manage or write stories on, it will just stop pulling data down after a while. It's very random when it happens, but probably happens once a week. If effects everyone who is accessing the site from this connection, and I can access other sites no problem. Also, if I go outside the office back home, which is right down the street, and access the site it is fine. I'm using Comcast in both locations. It's almost as if I have a limit on requests to each site and have hit my limit so it blocks the site for a while. Anybody have any clue what this might be?

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• Ios Game with many animated Nodes,performance issues

  - by user31929

  I'm working in a large map upside-down game(not tiled map),the map i use is a city. I have to insert many node to create the "life of the city",something like people that cross the streets,cars,etc... Some of this characters are involved in physics and game logic but others are only graphic characters. For what i know the only way i can achive this result is to create each character node with or without physic body and animate each character with a texture atlas. In this way i think that i'll have many performance problems, (the characters will be something like 100/150) even if i'll apply all the performance tips that i know... My question is: with large numbers of characters there another programming pattern that i must follow ? What is the approch of game like simcity,simpsons tapped out for ios,etc... that have so many animation at the same time?

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• Best way to go about sorting 2D sprites in a "RPG Maker" styled RPG

  - by Aaron Stewart

  I am trying to come up with the best way to create overlapping sprites without having any issues. I was thinking of having a SortedDictionary and setting the Entity's key to it's Y position relative to the max bound of the simulation, aka the Z value. I'd update the "Z" value in the update method each frame, if the entity's position has changed at all. For those who don't know what I mean, I want characters who are standing closer in front of another character to be drawn on top, and if they are behind the character, they are drawn behind. I'm leery of using SpriteBatch back to front or front to back, I've been doing some searching and have been under the impression they are a bad idea. and want to know exactly how other people are dealing with their depth sorting. Just ultimately trying to come up with the best method of sorting for good practice before I get too far in to refactor the system effectively.

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• Improve Your Google Search Skills [Infographic]

  - by Jason Fitzpatrick

  Don’t limit yourself to just plugging in simple search terms to Google; check out this infographic and learn a search string search or two. You don’t need to limit yourself to searching just for simple strings; Google supports all manner of handy search tricks. If you want to search just HowToGeek.com’s archive of XBMC articles, for example, you can plug in site:howtogeek.com XBMC to search our site. Get More Out of Google [HackCollege via Mashable] How to See What Web Sites Your Computer is Secretly Connecting To HTG Explains: When Do You Need to Update Your Drivers? How to Make the Kindle Fire Silk Browser *Actually* Fast!

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• Switch encoding of terminal with a command

  - by Tomas Lycken

  One of the servers I quite often ssh to uses western encoding instead of utf-8 (and there's no way I can change that). I've started writing a bash script to connect to this server, so I won't have to type out the entire address every time, but I would like to improve this script so it also changes the encoding of the terminal window correctly. The change I need to do can be performed using the mouse by navigating to "Terminal"-"Set Character Encoding..."-"Western (ISO-8859-1)". Is there a terminal command that does the same thing, for the current terminal window/screen? To clarify: I'm not interested in ways of switching the locale of the system on the remote site - that system is administered by someone else, and I have no idea what stuff might depend on the latin-1 encoding there. What I want to do is to let this terminal window on my side switch character encoding to the above mentioned, in the same way I can do with my mouse and the menus.

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• Maintain proper symbol order when applying an armature in flash

  - by Michael Taufen

  I am trying to animate a character's leg in flash CS 5.5 for a game I am working on. I decided to use the bone tool because it's awesome. The problem I am having, however, is that for my character to be animated properly, the symbols that make up his leg (upper leg, lower leg, and shoe) need to be on top of each other in a specific way (otherwise the shoe looks like its next to the leg, etc). Applying the bones results in the following problem: the first symbol I apply it to is placed in the rear on the armature layer, the next on top of it, and so on, until the final symbol is already on top. I need them to be in the opposite order, but arrange send to back does nothing on the armature layer. How can I fix this? tl;dr: The bone tool is not maintaining the stacking order of my objects, please help. Thanks for helping :).

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• Including Specific Characters with Google Web Fonts

  - by S.K.

  I'm using the Open Sans web font from Google Web Fonts on my website. I only need the basic latin subset, but I do use the Psi (?) character quite often as well and I would like to use the Open Sans version of that character, without having to include the entire greek subset. I looked at this help page which shows how to embed specific characters only using the text parameter, but there's no mention of including specific characters. I tried doing the following to try to combine both font requests into one, but it didn't end up working. <link href='http://fonts.googleapis.com/css?family=Open+Sans:400,400italic,700&subset=latin' rel='stylesheet' type='text/css'> <link href='http://fonts.googleapis.com/css?family=Open+Sans:400,400italic,700&text=%CE%A8' rel='stylesheet' type='text/css'> Is there anyway to accomplish this?

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• C#/.NET Little Wonders: Static Char Methods

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Often times in our code we deal with the bigger classes and types in the BCL, and occasionally forgot that there are some nice methods on the primitive types as well.  Today we will discuss some of the handy static methods that exist on the char (the C# alias of System.Char) type. The Background I was examining a piece of code this week where I saw the following: 1: // need to get the 5th (offset 4) character in upper case 2: var type = symbol.Substring(4, 1).ToUpper(); 3:  4: // test to see if the type is P 5: if (type == "P") 6: { 7: // ... do something with P type... 8: } Is there really any error in this code?  No, but it still struck me wrong because it is allocating two very short-lived throw-away strings, just to store and manipulate a single char: The call to Substring() generates a new string of length 1 The call to ToUpper() generates a new upper-case version of the string from Step 1. In my mind this is similar to using ToUpper() to do a case-insensitive compare: it isn’t wrong, it’s just much heavier than it needs to be (for more info on case-insensitive compares, see #2 in 5 More Little Wonders). One of my favorite books is the C++ Coding Standards: 101 Rules, Guidelines, and Best Practices by Sutter and Alexandrescu.  True, it’s about C++ standards, but there’s also some great general programming advice in there, including two rules I love:         8. Don’t Optimize Prematurely         9. Don’t Pessimize Prematurely We all know what #8 means: don’t optimize when there is no immediate need, especially at the expense of readability and maintainability.  I firmly believe this and in the axiom: it’s easier to make correct code fast than to make fast code correct.  Optimizing code to the point that it becomes difficult to maintain often gains little and often gives you little bang for the buck. But what about #9?  Well, for that they state: “All other things being equal, notably code complexity and readability, certain efficient design patterns and coding idioms should just flow naturally from your fingertips and are no harder to write then the pessimized alternatives. This is not premature optimization; it is avoiding gratuitous pessimization.” Or, if I may paraphrase: “where it doesn’t increase the code complexity and readability, prefer the more efficient option”. The example code above was one of those times I feel where we are violating a tacit C# coding idiom: avoid creating unnecessary temporary strings.  The code creates temporary strings to hold one char, which is just unnecessary.  I think the original coder thought he had to do this because ToUpper() is an instance method on string but not on char.  What he didn’t know, however, is that ToUpper() does exist on char, it’s just a static method instead (though you could write an extension method to make it look instance-ish). This leads me (in a long-winded way) to my Little Wonders for the day… Static Methods of System.Char So let’s look at some of these handy, and often overlooked, static methods on the char type: IsDigit(), IsLetter(), IsLetterOrDigit(), IsPunctuation(), IsWhiteSpace() Methods to tell you whether a char (or position in a string) belongs to a category of characters. IsLower(), IsUpper() Methods that check if a char (or position in a string) is lower or upper case ToLower(), ToUpper() Methods that convert a single char to the lower or upper equivalent. For example, if you wanted to see if a string contained any lower case characters, you could do the following: 1: if (symbol.Any(c => char.IsLower(c))) 2: { 3: // ... 4: } Which, incidentally, we could use a method group to shorten the expression to: 1: if (symbol.Any(char.IsLower)) 2: { 3: // ... 4: } Or, if you wanted to verify that all of the characters in a string are digits: 1: if (symbol.All(char.IsDigit)) 2: { 3: // ... 4: } Also, for the IsXxx() methods, there are overloads that take either a char, or a string and an index, this means that these two calls are logically identical: 1: // check given a character 2: if (char.IsUpper(symbol[0])) { ... } 3:  4: // check given a string and index 5: if (char.IsUpper(symbol, 0)) { ... } Obviously, if you just have a char, then you’d just use the first form.  But if you have a string you can use either form equally well. As a side note, care should be taken when examining all the available static methods on the System.Char type, as some seem to be redundant but actually have very different purposes.  For example, there are IsDigit() and IsNumeric() methods, which sound the same on the surface, but give you different results. IsDigit() returns true if it is a base-10 digit character (‘0’, ‘1’, … ‘9’) where IsNumeric() returns true if it’s any numeric character including the characters for ½, ¼, etc. Summary To come full circle back to our opening example, I would have preferred the code be written like this: 1: // grab 5th char and take upper case version of it 2: var type = char.ToUpper(symbol[4]); 3:  4: if (type == 'P') 5: { 6: // ... do something with P type... 7: } Not only is it just as readable (if not more so), but it performs over 3x faster on my machine:    1,000,000 iterations of char method took: 30 ms, 0.000050 ms/item.    1,000,000 iterations of string method took: 101 ms, 0.000101 ms/item. It’s not only immediately faster because we don’t allocate temporary strings, but as an added bonus there less garbage to collect later as well.  To me this qualifies as a case where we are using a common C# performance idiom (don’t create unnecessary temporary strings) to make our code better. Technorati Tags: C#,CSharp,.NET,Little Wonders,char,string

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• Tool for creating Spritesheet? and Tips

  - by Spooks

  I am looking for a tool that I can use to create sprite sheet easily. Right now I am using Illustrator, but I can never get the center of the character in the exact position, so it looks like it is moving around(even though its always in one place), while being loop through the sprite sheet. Is there any better tools that I can be using? Also what kind of tips would you give for working with a sprite sheet? Should I create each part of the character in individual layers (left arm, right arm, body, etc.) or everything at once? any other tips would also be helpful! thank you

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• Pointer initialization doubt

  - by Jestin Joy

  We could initialize a character pointer like this in C. char *c="test"; Where c points to the first character(t). But when I gave code like below. It gives segmentation fault. #include<stdio.h> #include<stdlib.h> main() { int *i; *i=0; printf("%d",*i); } But when I give #include<stdio.h> #include<stdlib.h> main() { int *i; i=(int *)malloc(2); *i=0; printf("%d",*i); } It works( gives output 0). Also when I give malloc(0), It also works( gives output 0). Please tell what is happening

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• Should I implement slugs with my already fairly long URLs?

  - by Earlz

  I'm considering implementing slugs in my blog. My blog uses MongoDB. One of the side-effects of using MongoDB is that it uses relatively long hex string IDs. Example before: http://lastyearswishes.com/blog/view/5070f025d1f1a5760fdfafac after: http://lastyearswishes.com/blog/view/5070f025d1f1a5760fdfafac/improvements-on-barelymvc Of course, that's a relatively short title.. I have some longer ones, but intend to limit the maximum character limit for slugs to something reasonable. At what point does a URL become so long that it hurts SEO instead of improves it? In this case, should I leave my URLs alone, or add slugs?

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• Working with packed dates in SSIS

  - by Jim Giercyk

  One of the challenges recently thrown my way was to read an EBCDIC flat file, decode packed dates, and insert the dates into a SQL table.  For those unfamiliar with packed data, it is a way to store data at the nibble level (half a byte), and was often used by mainframe programmers to conserve storage space.  In the case of my input file, the dates were 2 bytes long and  represented the number of days that have past since 01/01/1950.  My first thought was, in the words of Scooby, Hmmmmph?  But, I love a good challenge, so I dove in. Reading in the flat file was rather simple.  The only difference between reading an EBCDIC and an ASCII file is the Code Page option in the connection manager.  In my case, I needed to use Code Page 1140 for EBCDIC (I could have also used Code Page 37).       Once the code page is set correctly, SSIS can understand what it is reading and it will convert the output to the default code page, 1252.  However, packed data is either unreadable or produces non-alphabetic characters, as we can see in the preview window.   Column 1 is actually the packed date, columns 0 and 2 are the values in the rest of the file.  We are only interested in Column 1, which is a 2 byte field representing a packed date.  We know that 2 bytes of packed data can be stored in 1 byte of character data, so we are working with 4 packed digits in 2 character bytes.  If you are confused, stay tuned….this will make sense in a minute.   Right-click on your Flat File Source shape and select “Show Advanced Editor”. Here is where the magic begins. By changing the properties of the output columns, we can access the packed digits from each byte. By default, the Output Column data type is DT_STR. Since we want to look at the bytes individually and not the entire string, change the data type to DT_BYTES. Next, and most important, set UseBinaryFormat to TRUE. This will write the HEX VALUES of the output string instead of writing the character values.  Now we are getting somewhere! Next, you will need to use a Data Conversion shape in your Data Flow to transform the 2 position byte stream to a 4 position Unicode string containing the packed data.  You need the string to be 4 bytes long because it will contain the 4 packed digits.  Here is what that should look like in the Data Conversion shape: Direct the output of your data flow to a test table or file to see the results.  In my case, I created a test table.  The results looked like this:     Hold on a second!  That doesn't look like a date at all.  No, of course not.  It is a hex number which represents the days which have passed between 01/01/1950 and the date.  We have to convert the Hex value to a decimal value, and use the DATEADD function to get a date value.  Luckily, I have created a function to convert Hex to Decimal:   -- ============================================= -- Author:        Jim Giercyk -- Create date: March, 2012 -- Description:    Converts a Hex string to a decimal value -- ============================================= CREATE FUNCTION [dbo].[ftn_HexToDec] (     @hexValue NVARCHAR(6) ) RETURNS DECIMAL AS BEGIN     -- Declare the return variable here DECLARE @decValue DECIMAL IF @hexValue LIKE '0x%' SET @hexValue = SUBSTRING(@hexValue,3,4) DECLARE @decTab TABLE ( decPos1 VARCHAR(2), decPos2 VARCHAR(2), decPos3 VARCHAR(2), decPos4 VARCHAR(2) ) DECLARE @pos1 VARCHAR(1) = SUBSTRING(@hexValue,1,1) DECLARE @pos2 VARCHAR(1) = SUBSTRING(@hexValue,2,1) DECLARE @pos3 VARCHAR(1) = SUBSTRING(@hexValue,3,1) DECLARE @pos4 VARCHAR(1) = SUBSTRING(@hexValue,4,1) INSERT @decTab VALUES (CASE               WHEN @pos1 = 'A' THEN '10'                 WHEN @pos1 = 'B' THEN '11'               WHEN @pos1 = 'C' THEN '12'               WHEN @pos1 = 'D' THEN '13'               WHEN @pos1 = 'E' THEN '14'               WHEN @pos1 = 'F' THEN '15'               ELSE @pos1              END, CASE               WHEN @pos2 = 'A' THEN '10'                 WHEN @pos2 = 'B' THEN '11'               WHEN @pos2 = 'C' THEN '12'               WHEN @pos2 = 'D' THEN '13'               WHEN @pos2 = 'E' THEN '14'               WHEN @pos2 = 'F' THEN '15'               ELSE @pos2              END, CASE               WHEN @pos3 = 'A' THEN '10'                 WHEN @pos3 = 'B' THEN '11'               WHEN @pos3 = 'C' THEN '12'               WHEN @pos3 = 'D' THEN '13'               WHEN @pos3 = 'E' THEN '14'               WHEN @pos3 = 'F' THEN '15'               ELSE @pos3              END, CASE               WHEN @pos4 = 'A' THEN '10'                 WHEN @pos4 = 'B' THEN '11'               WHEN @pos4 = 'C' THEN '12'               WHEN @pos4 = 'D' THEN '13'               WHEN @pos4 = 'E' THEN '14'               WHEN @pos4 = 'F' THEN '15'               ELSE @pos4              END) SET @decValue = (CONVERT(INT,(SELECT decPos4 FROM @decTab)))         +                 (CONVERT(INT,(SELECT decPos3 FROM @decTab))*16)      +                 (CONVERT(INT,(SELECT decPos2 FROM @decTab))*(16*16)) +                 (CONVERT(INT,(SELECT decPos1 FROM @decTab))*(16*16*16))     RETURN @decValue END GO     Making use of the function, I found the decimal conversion, added that number of days to 01/01/1950 and FINALLY arrived at my “unpacked relative date”.  Here is the query I used to retrieve the formatted date, and the result set which was returned: SELECT [packedDate] AS 'Hex Value',        dbo.ftn_HexToDec([packedDate]) AS 'Decimal Value',        CONVERT(DATE,DATEADD(day,dbo.ftn_HexToDec([packedDate]),'01/01/1950'),101) AS 'Relative String Date'   FROM [dbo].[Output Table]         This technique can be used any time you need to retrieve the hex value of a character string in SSIS.  The date example may be a bit difficult to understand at first, but with SSIS becoming the preferred tool for enterprise level integration for many companies, there is no doubt that developers will encounter these types of requirements with regularity in the future. Please feel free to contact me if you have any questions.

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• Week in Geek: Malware-Infected Web Sites Doubled Since Last Year

  - by Asian Angel

  This week we learned how to get spelling autocorrect across all applications on a Windows system, “diagnose DSL hang ups, extract media files from PowerPoint presentations, & restrict IE to a single website”, customize the Ubuntu bootloader screen, get smartphone-style word suggestion on Windows systems, learned what character encodings are and how they differ, and more. Photo by Profound Whatever.HTG Explains: What Are Character Encodings and How Do They Differ?How To Make Disposable Sleeves for Your In-Ear MonitorsMacs Don’t Make You Creative! So Why Do Artists Really Love Apple?

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• Detect collision from a particular side

  - by Fabián

  I'm making a platform sidescrolling game. All I want to do is to detect if my character is on the floor: function OnCollisionStay (col : Collision){ if(col.gameObject.tag == "Floor"){ onFloor = true; } else {onFloor = false;} } function OnCollisionExit (col : Collision){ onFloor = false; } But I know this isn't the accurate way. If I hit a cube with a "floor" tag, in the air (no matter if with the character's feet or head) I would be able to jump. Is there a way to use the same box collision to detect if I'm touching something from a specific side?

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• Should UTF-16 be considered harmful?

  - by Artyom

  I'm going to ask what is probably quite a controversial question: "Should one of the most popular encodings, UTF-16, be considered harmful?" Why do I ask this question? How many programmers are aware of the fact that UTF-16 is actually a variable length encoding? By this I mean that there are code points that, represented as surrogate pairs, take more than one element. I know; lots of applications, frameworks and APIs use UTF-16, such as Java's String, C#'s String, Win32 APIs, Qt GUI libraries, the ICU Unicode library, etc. However, with all of that, there are lots of basic bugs in the processing of characters out of BMP (characters that should be encoded using two UTF-16 elements). For example, try to edit one of these characters: 𝄞 (U+1D11E) MUSICAL SYMBOL G CLEF 𝕥 (U+1D565) MATHEMATICAL DOUBLE-STRUCK SMALL T 𝟶 (U+1D7F6) MATHEMATICAL MONOSPACE DIGIT ZERO 𠂊 (U+2008A) Han Character You may miss some, depending on what fonts you have installed. These characters are all outside of the BMP (Basic Multilingual Plane). If you cannot see these characters, you can also try looking at them in the Unicode Character reference. For example, try to create file names in Windows that include these characters; try to delete these characters with a "backspace" to see how they behave in different applications that use UTF-16. I did some tests and the results are quite bad: Opera has problem with editing them (delete required 2 presses on backspace) Notepad can't deal with them correctly (delete required 2 presses on backspace) File names editing in Window dialogs in broken (delete required 2 presses on backspace) All QT3 applications can't deal with them - show two empty squares instead of one symbol. Python encodes such characters incorrectly when used directly u'X'!=unicode('X','utf-16') on some platforms when X in character outside of BMP. Python 2.5 unicodedata fails to get properties on such characters when python compiled with UTF-16 Unicode strings. StackOverflow seems to remove these characters from the text if edited directly in as Unicode characters (these characters are shown using HTML Unicode escapes). WinForms TextBox may generate invalid string when limited with MaxLength. It seems that such bugs are extremely easy to find in many applications that use UTF-16. So... Do you think that UTF-16 should be considered harmful?

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• Calculus? Need help solving for a time-dependent variable given some other variables.

  - by user451527

  Long story short, I'm making a platform game. I'm not old enough to have taken Calculus yet, so I know not of derivatives or integrals, but I know of them. The desired behavior is for my character to automagically jump when there is a block to either side of him that is above the one he's standing on; for instance, stairs. This way the player can just hold left / right to climb stairs, instead of having to spam the jump key too. The issue is with the way I've implemented jumping; I've decided to go mario-style, and allow the player to hold 'jump' longer to jump higher. To do so, I have a 'jump' variable which is added to the player's Y velocity. The jump variable increases to a set value when the 'jump' key is pressed, and decreases very quickly once the 'jump' key is released, but decreases less quickly so long as you hold the 'jump' key down, thus providing continuous acceleration up as long as you hold 'jump.' This also makes for a nice, flowing jump, rather than a visually jarring, abrupt acceleration. So, in order to account for variable stair height, I want to be able to calculate exactly what value the 'jump' variable should get in order to jump exactly to the height of the stair; preferably no more, no less, though slightly more is permissible. This way the character can jump up steep or shallow flights of stairs without it looking weird or being slow. There are essentially 5 variables in play: h -the height the character needs to jump to reach the stair top<br> j -the jump acceleration variable<br> v -the vertical velocity of the character<br> p -the vertical position of the character<br> d -initial vertical position of the player minus final position<br> Each timestep:<br> j -= 1.5; //the jump variable's deceleration<br> v -= j; //the jump value's influence on vertical speed<br> v *= 0.95; //friction on the vertical speed<br> v += 1; //gravity<br> p += v; //add the vertical speed to the vertical position<br> v-initial is known to be zero<br> v-final is known to be zero<br> p-initial is known<br> p-final is known<br> d is known to be p-initial minus p-final<br> j-final is known to be zero<br> j-initial is unknown<br> Given all of these facts, how can I make an equation that will solve for j? tl;dr How do I Calculus? Much thanks to anyone who's made it this far and decides to plow through this problem.

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• How do I implement smooth movement in a Box2D platform game?

  - by Romeo

  I have implemented a character in JBox2D which moves with the help of a wheel rotating at the bottom of it. The movement is the best result I've had 'till now but it's a little glitchy when the character stands on the edge. So I am thinking should I use five smaller wheels instead of a big wheel. The wheel/wheels will not be visible in the finished product, now they are drawn for debugging. Here is a video. Is there a better way to do this using JBox2D?

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• Is there a way to export all the images of my tweening effect in Flash?

  - by Paul

  i'm using Flash to create the animation of my character in 2D (i'm just beginning). Is it possible to make a tween effect of a character, and then automatically export all the images/frames? So far, it's a bit fastidious : i create my tweening effect, then i put a keyframe for each frame i want to copy and paste, then i select the movieclips and shapes and copy and paste them into another flash document, i position those clips at the exact same location as the previous image, then i erase the previous image and export the image... For 30 frames! Is there any faster way? Thanks

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• 2d Ice movement

  - by Jeremy Clarkson

  I am building an top-down 2d RPG like zelda. I have been trying to implement ice sliding. I have a tile with the slide property. I thought it would be easy to get working. I figured that I would read the slide property, and move the character forward until the slide property no longer exists. So I tried a loop but all it did was stop at the first tile in an infinite loop. I then took the loop out and tried taking direct control of the character to move him along the slide path but I couldn't get it to move. Is there an easy way to do an ice sliding tile based movement in libgdx. I looked for a tutorial but none exist.

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• Inside OCP - "Managing Database Resources"

  New features in Oracle Database 11g help you assess performance and limit I/O usage.

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• Subterranean IL: The ThreadLocal type

  - by Simon Cooper

  I came across ThreadLocal<T> while I was researching ConcurrentBag. To look at it, it doesn't really make much sense. What's all those extra Cn classes doing in there? Why is there a GenericHolder<T,U,V,W> class? What's going on? However, digging deeper, it's a rather ingenious solution to a tricky problem. Thread statics Declaring that a variable is thread static, that is, values assigned and read from the field is specific to the thread doing the reading, is quite easy in .NET: [ThreadStatic] private static string s_ThreadStaticField; ThreadStaticAttribute is not a pseudo-custom attribute; it is compiled as a normal attribute, but the CLR has in-built magic, activated by that attribute, to redirect accesses to the field based on the executing thread's identity. TheadStaticAttribute provides a simple solution when you want to use a single field as thread-static. What if you want to create an arbitary number of thread static variables at runtime? Thread-static fields can only be declared, and are fixed, at compile time. Prior to .NET 4, you only had one solution - thread local data slots. This is a lesser-known function of Thread that has existed since .NET 1.1: LocalDataStoreSlot threadSlot = Thread.AllocateNamedDataSlot("slot1"); string value = "foo"; Thread.SetData(threadSlot, value); string gettedValue = (string)Thread.GetData(threadSlot); Each instance of LocalStoreDataSlot mediates access to a single slot, and each slot acts like a separate thread-static field. As you can see, using thread data slots is quite cumbersome. You need to keep track of LocalDataStoreSlot objects, it's not obvious how instances of LocalDataStoreSlot correspond to individual thread-static variables, and it's not type safe. It's also relatively slow and complicated; the internal implementation consists of a whole series of classes hanging off a single thread-static field in Thread itself, using various arrays, lists, and locks for synchronization. ThreadLocal<T> is far simpler and easier to use. ThreadLocal ThreadLocal provides an abstraction around thread-static fields that allows it to be used just like any other class; it can be used as a replacement for a thread-static field, it can be used in a List<ThreadLocal<T>>, you can create as many as you need at runtime. So what does it do? It can't just have an instance-specific thread-static field, because thread-static fields have to be declared as static, and so shared between all instances of the declaring type. There's something else going on here. The values stored in instances of ThreadLocal<T> are stored in instantiations of the GenericHolder<T,U,V,W> class, which contains a single ThreadStatic field (s_value) to store the actual value. This class is then instantiated with various combinations of the Cn types for generic arguments. In .NET, each separate instantiation of a generic type has its own static state. For example, GenericHolder<int,C0,C1,C2> has a completely separate s_value field to GenericHolder<int,C1,C14,C1>. This feature is (ab)used by ThreadLocal to emulate instance thread-static fields. Every time an instance of ThreadLocal is constructed, it is assigned a unique number from the static s_currentTypeId field using Interlocked.Increment, in the FindNextTypeIndex method. The hexadecimal representation of that number then defines the specific Cn types that instantiates the GenericHolder class. That instantiation is therefore 'owned' by that instance of ThreadLocal. This gives each instance of ThreadLocal its own ThreadStatic field through a specific unique instantiation of the GenericHolder class. Although GenericHolder has four type variables, the first one is always instantiated to the type stored in the ThreadLocal<T>. This gives three free type variables, each of which can be instantiated to one of 16 types (C0 to C15). This puts an upper limit of 4096 (163) on the number of ThreadLocal<T> instances that can be created for each value of T. That is, there can be a maximum of 4096 instances of ThreadLocal<string>, and separately a maximum of 4096 instances of ThreadLocal<object>, etc. However, there is an upper limit of 16384 enforced on the total number of ThreadLocal instances in the AppDomain. This is to stop too much memory being used by thousands of instantiations of GenericHolder<T,U,V,W>, as once a type is loaded into an AppDomain it cannot be unloaded, and will continue to sit there taking up memory until the AppDomain is unloaded. The total number of ThreadLocal instances created is tracked by the ThreadLocalGlobalCounter class. So what happens when either limit is reached? Firstly, to try and stop this limit being reached, it recycles GenericHolder type indexes of ThreadLocal instances that get disposed using the s_availableIndices concurrent stack. This allows GenericHolder instantiations of disposed ThreadLocal instances to be re-used. But if there aren't any available instantiations, then ThreadLocal falls back on a standard thread local slot using TLSHolder. This makes it very important to dispose of your ThreadLocal instances if you'll be using lots of them, so the type instantiations can be recycled. The previous way of creating arbitary thread-static variables, thread data slots, was slow, clunky, and hard to use. In comparison, ThreadLocal can be used just like any other type, and each instance appears from the outside to be a non-static thread-static variable. It does this by using the CLR type system to assign each instance of ThreadLocal its own instantiated type containing a thread-static field, and so delegating a lot of the bookkeeping that thread data slots had to do to the CLR type system itself! That's a very clever use of the CLR type system.

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• how difficult to add vibration/feedback to a open source driving game

  - by Jonathan Day

  Hi, I'm looking to use SuperTuxKart as a basis for a PhD research project. A key requirement for the game is to provide vibration feedback through the controller (obviously dependant on the controller itself). I don't believe that the game currently includes this feature and I'm trying to get a feel for how big a challenge it would be to add. My background is as a J2EE and PHP developer/architect, so I don't know C++ as such, but am prepared to give it a crack if there are resources and guides to assist, and it's not a herculean task. Alternatively, if you know of any open source games that do include vibration feedback, please feel free to let me know! Preferably the game would be of the style that the player had to navigate a character (or character's vehicle) over a repeatable course/map. TIA, JD

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