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• Simulating smooth movement along a line after calculating a collision containing a restitution of zero in 2D

  - by Casey

  [for tl;dr see after listing] //...Code to determine shapes types involved in collision here... //...Rectangle-Line collision detected. if(_rbTest->GetCollisionShape()->Intersects(*_ground->GetCollisionShape())) { //Convert incoming shape to a line. a2de::Line l(*dynamic_cast<a2de::Line*>(_ground->GetCollisionShape())); //Get line's normal. a2de::Vector2D normal_vector(l.GetSlope().GetY(), -l.GetSlope().GetX()); a2de::Vector2D::Normalize(normal_vector); //Accumulate forces involved. a2de::Vector2D intermediate_forces; a2de::Vector2D normal_force = normal_vector * _rbTest->GetMass() * _world->GetGravityHandler()->GetGravityValue(); intermediate_forces += normal_force; //Calculate final velocity: See [1] double Ma = _rbTest->GetMass(); a2de::Vector2D Ua = _rbTest->GetVelocity(); double Mb = _ground->GetMass(); a2de::Vector2D Ub = _ground->GetVelocity(); double mCr = Mb * _ground->GetRestitution(); a2de::Vector2D collision_velocity( ((Ma * Ua) + (Mb * Ub) + ((mCr * Ub) - (mCr * Ua))) / (Ma + Mb)); //Calculate reflection vector: See [2] a2de::Vector2D reflect_velocity( -collision_velocity + 2 * (a2de::Vector2D::DotProduct(collision_velocity, normal_vector)) * normal_vector ); //Affect velocity to account for restitution of colliding bodies. reflect_velocity *= (_ground->GetRestitution() * _rbTest->GetRestitution()); _rbTest->SetVelocity(reflect_velocity); //THE ULTIMATE ISSUE STEMS FROM THE FOLLOWING LINE: //Move object away from collision one pixel to prevent constant collision. _rbTest->SetPosition(_rbTest->GetPosition() + normal_vector); _rbTest->ApplyImpulse(intermediate_forces); } Sources: (1) Wikipedia: Coefficient of Restitution: Speeds after impact (2) Wikipedia: Specular Reflection: Direction of reflection First, I have a system in place to account for friction (that is, a coefficient of friction) but is not used right now (in addition, it is zero, which should not affect the math anyway). I'll deal with that after I get this working. Anyway, when the restitution of either object involved in the collision is zero the object stops as required, but if movement along the same direction (again, irrespective of the friction value that isn't used) as the line is attempted the object moves as if slogging through knee deep snow. If I remove the line of code in question and the object is not push away one pixel the object barely moves at all. All because the object collides, is stopped, is pushed up, collides, is stopped...etc. OR collides, is stopped, collides, is stopped, etc... TL;DR How do I only account for a collision ONCE for restitution purposes (BONUS: but CONTINUALLY for frictional purposes, to be implemented later)

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• Two graphical entities, smooth blending between them (e.g. asphalt and grass)

  - by Gabriel Conrad

  Supposedly in a scenario there are, among other things, a tarmac strip and a meadow. The tarmac has an asphalt texture and its model is a triangle strip long that might bifurcate at some point into other tinier strips, and suppose that the meadow is covered with grass. What can be done to make the two graphical entities seem less cut out from a photo and just pasted one on top of the other at the edges? To better understand the problem, picture a strip of asphalt and a plane covered with grass. The grass texture should also "enter" the tarmac strip a little bit at the edges (i.e. feathering effect). My ideas involve two approaches: put two textures on the tarmac entity, but that involves a serious restriction in how the strip is modeled and its texture coordinates are mapped or try and apply a post-processing filter that mimics a bloom effect where "grass" is used instead of light. This could be a terrible failure to achieve correct results. So, is there a better or at least a more obvious way that's widely used in the game dev industry?

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• How can I implement smooth rotation from one direction to another?

  - by user1759052

  I'm having a problem with animating rotations with 1Matrix.CreateRotationY() with my basic 3D game. Based on where you click the mouse, I want the 3D object to rotate to that direction and then move. I am using this to determine the target direction: float rot = (float)(Math.Atan2(X, Z)); It gives me the correct value, but I am not sure how to handle the rotation animation from current direction to new direction. I've tried a few things, but to no avail. Do you guys know of any good ways of solving this issue?

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• How to list column headers of a SQL Server table using sp_help perhaps?

  - by Hamish Grubijan

  Hi, I have a few tables with 70-80 columns in them. I would like to populate them with somewhat random data, unless I will not be able to do so due to key violation, etc. The first step would be simply to get the list of all headers. There seem to be two ways: A) Run select * from table_of_interest; in MSFT SQL Server Management Studio 2008. Now, right-click the result and click "Copy With headers". However, I get zero rows back, and when I try to copy nothing + headers, I get: TITLE: Microsoft SQL Server Management Studio ------------------------------ Value cannot be null. Parameter name: data (System.Windows.Forms) ------------------------------ BUTTONS: OK ------------------------------ This looks like a bug ... anyhow ... there is another way. B) I can run sp_help table_of_interest;. However, I end up getting too much back. I get 7 different tables back but I am only interested in the second one. The columns of the second table are: Column_name | Type | Computed | Length | Prec | Scale | Nullable | TrimTrailingBlanks | FixedLenNullInSource | Collation I might be interested in just a Column_name and Type, but maybe other columns. So ... since sp_help probably runs a bunch of queries ... how do I get under the hood? How can I run the second query AND filter down the number of columns that I am interested in? Many Thanks!

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• Method overloads resolution and Jon Skeet's Brain Teasers

  - by runrunraygun

  Jon's Brain Teasers Here Be Spoilers... I'm looking at the answer to #1, and I must admit I never knew this was the case in overload resolution. But why is this the case. In my tiny mind Derived.Foo(int) seems like the logical route to go down. What is the logic behind this design decision?

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• Is the 'Is' VB.NET keyword the same as Object.ReferenceEquals?

  - by Shimmy

  Is the Is VB.NET keyword the same as Object.ReferenceEquals?

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• How do boost operators work?

  - by FredOverflow

  boost::operators automatically defines operators like + based on manual implementations like += which is very useful. To generate those operators for T, one inherits from boost::operators<T> as shown by the boost example: class MyInt : boost::operators<MyInt> I am familiar with the CRTP pattern, but I fail to see how it works here. Specifically, I am not really inheriting any facilities since the operators aren't members. boost::operators seems to be completely empty, but I'm not very good at reading boost source code. Could anyone explain how this works in detail? Is this mechanism well-known and widely used?

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• how to handle delete by illegal address

  - by Davit Siradeghyan

  Suppose we have a situation like this. How to handle this problem? How to protect code from crashes? I know about and use boost smart pointers. But what to do if we have this situation. struct Test { int a; int b; int c; }; Test global; int main() { Test *p = new Test; p->a = 1; p->b = 2; p->c = 3; p = &global; delete p; return 0; }

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• Why is this code invalid in C#?

  - by mmattax

  The following code will not compile: string foo = "bar"; Object o = foo == null ? DBNull.Value : foo; I get: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DBNull' and 'string' To fix this, I must do something like this: string foo = "bar"; Object o = foo == null ? DBNull.Value : (Object)foo; This cast seems pointless as this is certainly legal: string foo = "bar"; Object o = foo == null ? "gork" : foo; It seems to me that when the ternary branches are of different types, the compiler will not autobox the values to the type object...but when they are of the same type then the autoboxing is automatic. In my mind the first statement should be legal... Can anyone describe why the compiler does not allow this and why the designers of C# chose to do this? I believe this is legal in Java...Though I have not verified this. Thanks. EDIT: I am asking for an understanding of why Java and C# handle this differently, what is going on underneath the scenes in C# that make this invalid. I know how to use ternary, and am not looking for a "better way" to code the examples. I understand the rules of ternary in C#, but I want to know WHY... EDIT (Jon Skeet): Removed "autoboxing" tag as no boxing is involved in this question.

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• Bitwise AND, Bitwise Inclusive OR question, in Java

  - by Dave

  I've a few lines of code within a project, that I can't see the value of... buffer[i] = (currentByte & 0x7F) | (currentByte & 0x80); It reads the filebuffer from a file, stored as bytes, and then transfers then to buffer[i] as shown, but I can't understand what the overall purpose is, any ideas? Thanks

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• What does "<<" mean in C#?

  - by Simon G

  Hi, Basically the questions in the title. I'm looking at the MVC 2 source code: public enum HttpVerbs { Get = 1 << 0, Post = 1 << 1, Put = 1 << 2, Delete = 1 << 3, Head = 1 << 4 } and I'm just curious as to what "<<" does. Thanks

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• can i overload a method with another one that takes the same parameters but has a diferent return ty

  - by David

  For example can i have something like this: public static void SAMENAME (sameparameter n) { some code ; } public static String SAMENAME (sameparameter n) { similar code; return someString ; }

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• using LIKE with logical operators

  - by ryanthegecko

  i can't seem to figure out how to combine LIKE with an OR or AND: DELETE * FROM persons WHERE FirstName = 'Abe' AND LastName LIKE '%coln'; Looks like it should owrk to me but I get error 1064 (syntax0 Is there a correct way to do this?

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• Implementing __concat__

  - by Casebash

  I tried to implement __concat__, but it didn't work >>> class lHolder(): ... def __init__(self,l): ... self.l=l ... def __concat__(self, l2): ... return self.l+l2 ... def __iter__(self): ... return self.l.__iter__() ... >>> lHolder([1])+[2] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for +: 'lHolder' and 'list' How can I fix this?

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• C# Batching Process?

  - by pRoF3SoR BaLtHaZaR

  Hi, Can every body tell me by simple answer where & what i can create a batch process for ordinary operations such saving, changing file properties and so...

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• Should I use `!IsGood` or `IsGood == false`?

  - by chills42

  I keep seeing code that does checks like this if (IsGood == false) { DoSomething(); } or this if (IsGood == true) { DoSomething(); } I hate this syntax, and always use the following syntax. if (IsGood) { DoSomething(); } or if (!IsGood) { DoSomething(); } Is there any reason to use '== true' or '== false'? Is it a readability thing? Do people just not understand Boolean variables? Also, is there any performance difference between the two?

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• Dictionary keys don't contain a key that's already contained in keys

  - by ran

  Why is the following 'exist' boolean variable getting a value of false??? foreach (Cell existCell in this.decoratorByCell.Keys) { //this call yield the same hashcode for both cells. still exist==false bool exist = this.decoratorByCell.ContainsKey(existCell); } I've overridden GetHashCode() & Equals() Methods as follows: public override int GetHashCode() { string nodePath = GetNodePath(); return nodePath.GetHashCode() + m_ownerColumn.GetHashCode(); } public bool Equals(Cell other) { bool nodesEqual = (other.OwnerNode == null && this.OwnerNode == null) || (other.GetNodePath() == this.GetNodePath()); bool columnsEqual = (other.OwnerColumn == null && this.OwnerColumn == null) || (other.OwnerColumn == this.OwnerColumn); bool treesEqual = (this.m_ownerTree == other.m_ownerTree); return (nodesEqual && columnsEqual && treesEqual); }

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• SQL searching table fields with LIKE

  - by Tom Gullen

  Given your data stored somewhere in a database: Hello my name is Tom I like dinosaurs to talk about SQL. SQL is amazing. I really like SQL. We want to implement a site search, allowing visitors to enter terms and return relating records. A user might search for: Dinosaurs And the SQL: WHERE articleBody LIKE '%Dinosaurs%' Copes fine with returning the correct set of records. How would we cope however, if a user mispells dinosaurs? IE: Dinosores (Poor sore dino). How can we search allowing for error in spelling? We can associate common misspellings we see in search with the correct spelling, and then search on the original terms + corrected term, but this is time consuming to maintain. Any way programatically?

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• Linked List pop() function

  - by JKid314159

  Consider the following list: [LinkNode * head -- LinkNode * node1 -- LinkNode * node2] I'm creating a stack of FIFO. I Call pop() which I want to pop node1. LinkNode::LinkNode(int numIn) { this->numIn = numIn; next = null; } . . . int LinkNode::pop() { Link * temp = head->next; head = temp->next; int popped = head->nodeNum; delete temp; Return numOut; Question: 1) head should be a pointer or a LinkNode *? 2) Link * temp is created on the call stack and when pop finishes doesn't temp delete automatically? 3) My major confusion is on what is the value of temp-next? Does this point to node1.next which equals node2? Appreciate your help? My reference is C++ for Java Programmers by Weiss.

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• Can you explain what this code fragment is doing?

  - by coffeeaddict

  repeater.StartIndex = layout == ProductLayout.Grid4Columns ? startIndex - 1 : 0; I don't get it. What is layout == [expression] doing here in this case as it sets StartIndex Can somebody help explain what this code is doing?

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• Two '==' equality operators in same 'if' condition are not working as intended.

  - by Manav MN

  I am trying to establish equality of three equal variables, but the following code is not printing the obvious true answer which it should print. Can someone explain, how the compiler is parsing the given if condition internally? #include<stdio.h> int main() { int i = 123, j = 123, k = 123; if ( i == j == k) printf("Equal\n"); else printf("NOT Equal\n"); return 0; } Output: manav@workstation:~$ gcc -Wall -pedantic calc.c calc.c: In function ‘main’: calc.c:5: warning: suggest parentheses around comparison in operand of ‘==’ manav@workstation:~$ ./a.out NOT Equal manav@workstation:~$ EDIT: Going by the answers given below, is the following statement okay to check above equality? if ( (i==j) == (j==k))

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• VB.NET overloading array access?

  - by Wayne Werner

  Hi, Is it possible to overload the array/dict access operators in VB.net? For example, you can state something like: Dim mydict As New Hashtable() mydict.add("Cool guy", "Overloading is dangerous!") mydict("Cool guy") = "Overloading is cool!" And that works just fine. But what I would like to do is be able to say: mydict("Cool guy") = "3" and then have 3 automagically converted to the Integer 3. I mean, sure I can have a private member mydict.coolguy and have setCoolguy() and getCoolguy() methods, but I would prefer to be able to write it the former way if at all possible. Thanks

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• Index, assignment and increment in one statement behaves differently in C++ and C#. Why?

  - by Ivan Zlatanov

  Why is this example of code behaving differently in c++ and C#. [C++ Example] int arr[2]; int index = 0; arr[index] = ++index; The result of which will be arr[1] = 1; [C# Example] int[] arr = new int[2]; int index = 0; arr[index] = ++index; The result of which will be arr[0] = 1; I find this very strange. Surely there must be some rationale for both languages to implement it differently? I wonder what would C++/CLI output?

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• Linq like or other construction

  - by Yauhen Kavalenka

  I have DB oracle in my solution. I want to have some results in this query. Query example: select * from doctor where doctor.name like '%IVANOV_A%'; But if i do it at LINQ i cannot get any result. from p in repository.Doctor.Where(x => x.Name.ToLower().Containsname)) select p; Where 'name' is variable of string parameter. Web layout request next string: "Ivanov a" or "A Ivanov" But i suggest for user choose you pattetn for query. How i can to get "patient by name" if name consist of "First name" and "Last name" but user doesn't know your doctor's full name?

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• MySQL: Which is faster — INSTR or LIKE?

  - by Grekker

  If your goal is to test if a string exists in a MySQL column (of type 'varchar', 'text', 'blob', etc) which of the following is faster / more efficient / better to use, and why? Or, is there some other method that tops either of these? INSTR( columnname, 'mystring' ) > 0 vs columnname LIKE '%mystring%'

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