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fastcall22

Member Since 04 Feb 2008
Offline Last Active Yesterday, 08:35 PM

#5287824 How to randomize a string variable

Posted by fastcall22 on 20 April 2016 - 01:41 PM

Important note: The system time in seconds is generally used to seed a new random number generator. Random number generators created within the same second will generate the same sequence of numbers.

Therefore, you shouldn’t make that “somewhere” in “create a new random number generator somewhere in your code” be immediately before its use, but rather, as a member variable initialized at load-time.


#5287729 std::sort corrupts my memory

Posted by fastcall22 on 20 April 2016 - 01:16 AM

SMyStruct::operator< is an invalid comparator. Write a well formed comparator for SMyStruct to fix:
 
bool SMyStruct::operator< ( const SMyStruct& m ) const {
    return std::tie(x, y) < std::tie(m.x, m.y); 
}

// or 

bool SMyStruct::operator< ( const SMyStruct& m ) const {
    if ( x < m.x )  return true;
    if ( x > m.x )  return false;
    if ( y < m.y )  return true;
    return false;
}

(Also note that this is the typical implementation of operator< for tuples and pairs.)


What compiler are you using? I can’t remember the last time anybody’s needed to add whitespace between right angle brackets in a template typename...


#5287692 Efficient click detection design

Posted by fastcall22 on 19 April 2016 - 04:53 PM

Either through elaborate GUI systems or something as simple by transforming the coordinates into an index into a list of items.


#5287647 FizzBuzz: Enterprise Edition!

Posted by fastcall22 on 19 April 2016 - 01:47 PM

For those not familiar with fizzbuzz: http://c2.com/cgi/wiki?FizzBuzzTest

There is an “enterprise implementation” of fizzbuzz available on GitHub: https://github.com/EnterpriseQualityCoding/FizzBuzzEnterpriseEdition


And even more amusing are its open issues:
https://github.com/EnterpriseQualityCoding/FizzBuzzEnterpriseEdition/issues?page=4&q=is%3Aissue+is%3Aopen


Some of my favorites:
#141: *URGENT* *NEED HELP ASAP* I can't run this on my LG Optimus L9
#13: FIPS PUB 199 COMPLIANCE
#216: 6 Month Release Cycle
#214: Can we have a REST API?
#224: A Great Job Opportunity For You


Also: This looks like spam, but it’s not!!

Also:
Posting because these are hitting a little too close to home right now... :(


#5287403 HINSTANCE & HWND Corrupted when passed around functions

Posted by fastcall22 on 17 April 2016 - 10:53 PM

It seems to be a slicing of WinEventArgs due to a permissive interface. At the time of passing in args to func, an assignment from const WinEventArgs& to IEventArgs is made. Your callback then receives this copy and erroneously downcasts to WinEventArgs, and accesses invalid memory.

So the first step is to lock down your interface:
// How do I C++?
struct IEventArgs {
protected:
	IEventArgs() = default;
	~IEventArgs() = default;

public:
	IEventArgs(const IEventArgs&) = delete;
	IEventArgs& operator = (const IEventArgs&) = delete;
};
The next step is to stop using const references on small data types. Not only will you need to be extremely mindful of the lifetimes of the objects they refer to, but you also incur double-indirection.
 
struct WinEventArgs : public IEventArgs
{
	WinEventArgs(const int a, const int b) : a(a), b(b) { }

	const int a;
	const int b;
};
The general rule of thumb is to pass-by-reference objects that are expensive to copy.
POD-types (int, float, WPARAM, LPARAM) and handles (such as HINSTANCE, HWND) are all integral-types. Pass-by-value*.
A vector<int> with 25000 elements? Pass-by-reference.


EDIT:
With the updated code above, Visual Studio reports:
std::function<void(IEventArgs)> func = std::bind(&Component::test, cmp, std::placeholders::_1);
func(args);  // C2280: 'IEventArgs::IEventArgs(const IEventArgs &)': attempting to reference a deleted function



#5287263 HINSTANCE & HWND Corrupted when passed around functions

Posted by fastcall22 on 16 April 2016 - 11:16 PM

There isn’t enough code here to determine the actual cause (though I would first suspect the down-cast from IEventArgs& to WinEventArgs&). Setup a data breakpoint to see exactly when the value is corrupted.


#5287262 Multiple bullets?

Posted by fastcall22 on 16 April 2016 - 11:09 PM

Anyway, look into "std::vector".


Yes, you would be correct if the OP was using C++. But the tags on his topic states “Java,” so he should use java.util.ArrayList instead.

The same principles apply, though:
ArrayList<Bullet> bullets = new ArrayList<Bullet>();

bullets.add(new Bullet(x, y));

for ( Bullet b : bullets )
    b.update();
}    
At some point, you will need the ability to remove bullets. Use an iterator instead:
ListIterator<Bullet> itr = bullets.listIterator();
while ( itr.hasNext() )
    Bullet b = itr.next();

    if ( !b.update() )
        itr.remove();
}



#5287204 I can't build the Box2D physics library in Visual Studio 2015

Posted by fastcall22 on 16 April 2016 - 12:02 PM

You may have warning levels set on your project to treat warnings as errors (/WX). Usually these warnings indicate a possible bug with your code, but since this isn’t your code, you may be safe in ignoring these warnings.


Relevant code in b2CollideCircle:
	// Find the min separating edge.
	int32 normalIndex = 0;
	float32 separation = -b2_maxFloat;                            // (line 64)
	float32 radius = polygonA->m_radius + circleB->m_radius;
	int32 vertexCount = polygonA->m_count;
	const b2Vec2* vertices = polygonA->m_vertices;
	const b2Vec2* normals = polygonA->m_normals;

⋮
⋮

		b2Vec2 faceCenter = 0.5f * (v1 + v2);
		float32 separation = b2Dot(cLocal - faceCenter, normals[vertIndex1]);  // (line 141)
		if (separation > radius)
		{
			return;
		}



#5287130 Computing an optimized mesh from a number of spheres?

Posted by fastcall22 on 15 April 2016 - 08:57 PM

Take a look at constructive solid geometry, it may be what you’re looking for.


#5287093 My octagon is a circle and my pentagon is wonky :'(

Posted by fastcall22 on 15 April 2016 - 02:22 PM

To expand on what SotL said, here’s a brief history on Windows terminals.

Prior to Windows 10, terminals used the System Typeface, which was a bitmap font carried over from the IBM days, and consequently stuck on Code Page 437. Unicode support was nonexistent, but at least you had pixel-perfect characters to make your rouge-like game.

Starting with Windows 10, the terminal was completely reworked and now supports Unicode and uses TrueType fonts with modern font rendering. It’s smooth as silk, but you no longer have square characters nor pixel perfect box drawing.

Additionally, since the terminal supports Unicode, you need to use the Unicode code points rather than Code Page 437 code points:
Before: cout << (char)251; // √
After: wcout << L'√' /* or: */ << (wchar_t)0x221A;


So, here are some of your options:

1. Configure your terminal to use "Terminal" with an 8x8 font size. This is the easiest solution. Inserting wide characters should map to the original Code Page 437 code points: 0x221A -> 251.

2. Account for font proportions in your code. This involves scaling the Y-axis such that 1 unit along the Y-axis appears to be the same length as 1 unit along the X-axis, even if it doesn’t quite match up 1:1 to rows and columns.

3. Use U+2584, U+2580, and U+2588 (▄, ▀, and █ respectively) to split a character into two. This is trickier to do, as you would need to render to an "off-page" image before you can determine what characters to use. Don’t forget to use wcout to insert a “wide-character” into cout.


#5286570 C++ Rotating 2D shape in list

Posted by fastcall22 on 12 April 2016 - 09:48 PM

Dammit, why did I never learn cool properties of complex numbers when I was in school?!


Yeah dude. Complex numbers, bro: http://acko.net/blog/how-to-fold-a-julia-fractal/


#5285717 Frame Independent Problem

Posted by fastcall22 on 07 April 2016 - 11:06 PM

function Update(float timeElapsed)
{
velocity *= timeElapsed;
setPosition(getPosition() + velocity); // Now, update the entity position based on velocity
velocity = D3DXVECTOR3(0.0f, 0.0f, 0.0f);
...
...


The problem isn’t with the timers, but rather the units. The code is demoting velocity from units per second to units. For example:

1. Set velocity to 10 units per second (u/s).
2. Multiplying velocity by elapsed time in seconds (s) gives you a distance in units (u).
3. The result is then fed back into velocity-- reinterpret_casting from u to u/s, as it were. (BAD!)
4. Multiplying the new velocity in units with a the elapsed time gives you u*s units. (NO!)
5. Repeat steps 3-5, but with u*s^N units for velocity each iteration.


Be mindful of the units of your operands whenever you do any sort of math:
float3 distance_traveled = velocity * timeElapsed;  // u/s * s -> u
setPosition( getPosition() + distance_traveled );   // u + u -> u
If your intention was to have damping:
const float DAMPING = 0.8f;        // (scalar) reduces velocity 20% every 1 second (roughly) 
velocity *= DAMPING * timeElapsed; // u/s * scalar -> u/s
float3 distance_traveled = velocity * timeElapsed; // u/s * s -> u 
setPosition( getPosition() + velocity * timeElapsed ); // u + u -> u



#5285505 Data Structures Help!

Posted by fastcall22 on 06 April 2016 - 05:30 PM

See: C++ FAQ Lite: Why can’t I separate the definition of my templates class from its declaration and put it inside a .cpp file?

I like to separate my template classes into hpp, impl, and cpp. For template classes that have a handful of known types (such as a vector4_t<T> for T in (float, int)), then the cpp supplies all the definitions using hpp and impl for those types, and everything else won’t need to know about the impl. Otherwise, I have the hpp include the impl at the end of the file and forego having a cpp file.


#5284902 point inside convex quad, using only integers?

Posted by fastcall22 on 03 April 2016 - 01:56 PM

Fixed point math. Fixed point is just fancy integer math in different units.

For a 2’s complement 32-bit integer, you can represent the integers from 2^-32 to 2^32-1. Or, 2^0 to 2^31 with a sign bit.
A fixed float works in a similar manner, but by sliding the scale: 2^(0-N) to 2^(31-N) with a sign bit.

The math involved has a few extra steps, but it’s probably less costly than to use floating point math (on the target hardware, that is).


#5283453 Best Engine for a Hacking Game

Posted by fastcall22 on 25 March 2016 - 03:40 PM

Use a raw 80x25 16-color terminal. That’d be pretty tight.




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