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• Collision point of 2 curves in a 3d-room

  - by Frank

  Hello, i am programming a small game for quite some time. We started coding a small FPS-Shooter inside of a project at school to get a bit experience using directX. I dont know why, but i couldnt stop the project and started programming at home aswell. At the moment i am trying to create some small AI. Of cause thats definatlly not easy, but thats my personal goal anyways. The topic could prolly fill multiple books hehe. I've got the walking part of my bots done so far. They walk along a scriped path. I am not working on the "aiming" of the bots. While programming that i hit on some math problem i couldnt solve yet. I hope of your input on this to help me get further. Concepts, ideas and everything else are highly appreciated. Problem: Calculate the position (D3DXVECTOR3) where the curve of the projectile (depends on gravity, speed), hit the curved of the enemys walking path (depends on speed). We assume that the enemy walks in a constant line. Known variables: float projectilSpeed = 2000 m/s //speed of the projectile per second float gravitation = 9.81 m/s^2 //of cause the gravity lol D3DXVECTOR3 targetPosition //position of the target stored in a vector (x,y,z) D3DXVECTOR3 projectilePosition //position of the projectile D3DXVECTOR3 targetSpeed //stores the change of the targets position in the last second Variabledefinition ProjectilePosition at time of collision = ProjectilePos_t TargetPosition at time of collision = TargetPos_t ProjectilePosition at time 0, now = ProjectilePos_0 TargetPosition at time 0, now = TargetPos_0 Time to impact = t Aim-angle = theta My try: Found a formular to calculate "drop" (Drop of the projectile based on the gravity) on Wikipedia: float drop = 0.5f * gravity * t * t The speed of the projectile has a horizontal and a vertical part.. Found a formular for that on wikipedia aswell: ProjectilVelocity.x = projectilSpeed * cos(theta) ProjectilVelocity.y = projectilSpeed * sin(theta) So i would assume this is true for the projectile curve: ProjectilePos_t.x = ProjectilePos_0.x + ProjectileSpeed * t ProjectilePos_t.y = ProjectilePos_0.y + ProjectileSpeed * t + 0.5f * gravity * t * t ProjectilePos_t.z = ProjectilePos_0.z + ProjectileSpeed * t The target walk with a constant speed, so we can determine his curve by this: TargetPos_t = TargetPos_0 + TargetSpeed * D3DXVECTOR3(t, t, t) Now i dont know how to continue. I have to solve it somehow to get a hold on the time to impact somehow. As a basic formular i could use: float time = distanz / projectileSpeed But that wouldnt be truly correct as it would assume a linear "Trajectory". We just find this behaivor when using a rocket. I hope i was able to explain the problem as much as possible. If there are questions left, feel free to ask me! Greets from germany, Frank

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• Drive a POS printer via USB in c#

  - by JDibble

  Any ideas how i can best drive a USB POS printer from c#. POS printers are usually serial, TCP/IP or USB based. I know how to accomplish serial and TCP/IP but have no idea about communications through USB in C#. I know that there is a layer available from Microsoft called POS.NET, but I want to try and avoid using this. Any ideas or any C# libraries that people can recomend would be really appreciated. Thanks

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• What's the point of this in objective-c

  - by Mk12

  SomeObject *temp = [[SomeObject alloc] init] self.theObject = temp; [temp release]; Why is it always done that way? Why not self.theObject = [[SomeObject alloc] init];

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• Can bad stuff happen when dividing 1/a very small float?

  - by Jeremybub

  If I want to check that positive float A is less than the inverse square of another positive float B (in C99), could something go wrong if B is very small? I could imagine checking it like if(A<1/(B*B)) but if B is small enough, would this possibly result in infinity? If that were to happen, would the code still work correctly in all situations? in a similar vein, I might do if(1/A>B*B) Which might be slightly better because B*B might be zero if B is small (is this true?) Finally, a solution that I can't imagine being wrong is if(sqrt(1/A)>B) Which I don't think would ever result in zero division, but still might be problematic if A is close to zero. So basically, my questions are Can 1/X ever be infinity if X is greater than zero (but small)? Can X*X ever be zero if X is greater than zero? Will comparisons with infinity work the way I would expect them to?

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• Dynamically created image doesn't show when <img>'s src is refreshed to point to it

  - by Obay

  Hello, I have a javascript function generateGraph() { ... jQuery.get('chart.php?month='+month+'&year='+year); document.getElementById('graph').src = 'charts/'+month+'_'+year+'.png'; ... } which is called onChange. It basically creates, if not exists, or refreshes if already exists, a PNG image (using the first line above) and supposedly displays the generated image (using the second line above). The first line works, but the second one doesn't. Meaning, the image is generated, but the second line can't display the image, unless the page is reloaded, or if the image being referred to already existed before the page was loaded (meaning the 1st line just "refreshed" the image) Any ideas as to why this is and how to fix it? Thanks much for your help in advance!

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• Determine Android phone's proximity to known point while conserving power

  - by ahsteele

  I am trying to determine if an Android user has had a close proximity to a list of predetermined locations. I'd like to do this with the least amount of drain on the phone's battery. The two mechanisms I see for accomplishing this are proximity alerts and requesting location updates. What are the pros and cons of the two methods? Will one have less affect on the battery than the other? In either case I would guess the specific location manager used would affect power usage (existing Stack Overflow answer).

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• What's the point of setRetainsRegisteredObjects: ?

  - by dontWatchMyProfile

  Why would I want to set that to YES? What difference would that make? Must I worry about this?

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• Binary search to find the rotation point in a rotated sorted list

  - by Algorist

  I am having a sorted list which is rotated and I would like to do a binary search on that list to find the minimum element. Lets suppose initial list is {1,2,3,4,5,6,7,8} rotated list can be like {5,6,7,8,1,2,3,4} Normal binary search doesn't work in this case. Any idea how to do this.

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• PHP regex delimiter, what's the point?

  - by Evan Fosmark

  Why do PHP regexes have the surrounding delimiters? It seems like it would be more clear if any pattern modifiers were passed in as a parameter to whatever function was being used.

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• Feed paper on POS Printer C#

  - by evargas

  I've been trying to programatically feed the paper on a pos printer (Epson TM-U220D). The problem I have is that the last line of the document don't get printed, instead, it is printed as the first line of the next document printed. I tried POS for .NET sending the "ESC|flF" command, also tried to send the raw esc/pos command using the serial port, but it doesn't work. Any ideas?

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• C/C++ - Convert 24-bit signed integer to float

  - by e-t172

  I'm programming in C++. I need to convert a 24-bit signed integer (stored in a 3-byte array) to float (normalizing to [-1.0,1.0]). The platform is MSVC++ on x86 (which means the input is little-endian). I tried this: float convert(const unsigned char* src) { int i = src[2]; i = (i << 8) | src[1]; i = (i << 8) | src[0]; const float Q = 2.0 / ((1 << 24) - 1.0); return (i + 0.5) * Q; } I'm not entirely sure, but it seems the results I'm getting from this code are incorrect. So, is my code wrong and if so, why?

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• Round a double to 2 significant figures after decimal point

  - by Rajesh

  suppose if the value is 200.3456 it should be formatted to 200.34 or if it is 200 then it should be 200.00

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• calculating a gps coordinate given a point, bearing and distance

  - by user530509

  Hello, I have a problem which draws my back in some project for some time now. Im basically looking to trap a polygon using x,y points drawn by some script ive written. lat1,lon1 are the center gps cords of the polygon and im looking for its surrounding polygon. here is a part of my code in python: def getcords(lat1,lon1,dr,bearing): lat2=asin(sin(lat1)*cos(dr)+cos(lat1)*sin(dr)*cos(bearing)) lon2=lon1+atan2(sin(bearing)*sin(dr)*cos(lat1),cos(dr)-sin(lat1)*sin(lat2)) return [lat2,lon2] my input goes like this: lat1,lon1 - are given in decimal degrees. -dr is the angular computed by dividing the distance in miles by the earth's -raiuds(=3958.82) -bearing between 0-360 degrees. however for the input getcorsds1(42.189275,-76.85823,0.5/3958.82,30) i get [-1.3485899508698462, -76.8576637627568], however [42.2516666666667,-76.8097222222222] is the right answer. as for the angular distance i calculate it simply by dividing the distance in miles by the earth's raiuds(=3958.82). anybody?

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• How do calculators work with precision?

  - by zoul

  Hello! I wonder how calculators work with precision. For example the value of sin(M_PI) is not exactly zero when computed in double precision: #include <math.h> #include <stdio.h> int main() { double x = sin(M_PI); printf("%.20f\n", x); // 0.00000000000000012246 return 0; } Now I would certainly want to print zero when user enters sin(p). I can easily round somewhere on 1e–15 to make this particular case work, but that’s a hack, not a solution. When I start to round like this and the user enters something like 1e–20, they get a zero back (because of the rounding). The same thing happens when the user enters 1/10 and hits the = key repeatedly — when he reaches the rounding treshold, he gets zero. And yet some calculators return plain zero for sin(p) and at the same time they can work with expressions such as (1e–20)/10 comfortably. Where’s the trick?

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• Typecasting a floating value or using the math.h floor* functions?

  - by nobody

  Hi, I am coding up an implementation of Interpolation Search in C. The question is actually rather simple, I need to use the floating operations to do linear interpolation to find the correct index which will eventually be an integer result. In particular my probe index is: t = i + floor((((k-low)/(high-low)) * (j-i))); where, i,j,k,t are unsigned ints, and high,low are doubles. Would this be equivalent to: t = i + (unsigned int)(((k-low)/(high-low)) * (j-i)); Is there any reason I would actually want to use math.h floor* functions over just a simple (int) typecast?

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• Interview Q: find angle between hour and minute hands in an analog clock

  - by polygenelubricants

  I was given this interview question recently: An analog clock shows that the current time is HH:MM. Compute in degree, the smaller angle between the hour and minute hands. Be as precise as you can. I'm wondering what's the simplest, most readable, most precise algorithm is. Solution in any language is welcome (but do explain it a bit if you think it's necessary).

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• How do you change the image of a bullet point in LaTeX Beamer

  - by cheshirekow

  When I use the itemize environment, i.e. \begin{itemize} \item one \item two \item three \end{itemize} The bullet points are ugly bitmap graphics that have harsh (aliased) edges. I'd like it to be a nice, clean font character or vector graphic

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• How to compare two floating-point values in shell script

  - by Reem

  I had to do a division in shell script and the best way was: result1=`echo "scale=3; ($var1 / $total) * 100"| bc -l` result2=`echo "scale=3; ($var2 / $total) * 100"| bc -l` but I want to compare the values of $result1 and $result2 Using if test $result1 -lt $result2 or if [ $result1 -gt $result2 ] didn't work :( Any idea how to do that?

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• How to mark empty in a single element in a float array

  - by Vineeth Mohan

  I have a large float (primitive) array and not every element in the array is filled. How can i mark a particular element as EMPTY. I understand this can be achieved by some special symbols but still i would like to know the standard way. Even if i am using some special symbol , how will i handle a situation where the actual data item is the value of special symbol. In short my question is how to implement the NULL feature in a primitive type array in java. PS - The reason why i am not using Float object is to achieve a high memory and speed performance. Thanks Vineeth

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• Dont know how to stop element in certain point

  - by user713190

  Im beginner and im experimenting on a website with fixed and relative postions, what i want to do is to stop bottom part when the two bottom lines(div .top_divider_line) touches nav menu(div .top_holder) here is the preview from site where im stuck. http://elexoj.com/test/ I think making it with jquery will be lot easier but i've no idea how to do it, i'll really appreciate your help. Thank You!

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• Why might different computers calculate different arithmetic results in VB.NET?

  - by Eyal

  I have some software written in VB.NET that performs a lot of calculations, mostly extracting jpegs to bitmaps and computing calculations on the pixels like convolutions and matrix multiplication. Different computers are giving me different results despite having identical inputs. What might be the reason? Edit: I can't provide the algorithm because it's proprietary but I can provide all the relevant operations: ULong \ ULong (Turuncating division) Bitmap.Load("filename.bmp') (Load a bitmap into memory) Bitmap.GetPixel(Integer, Integer) (Get a pixel's brightness) Double + Double Double * Double Math.Sqrt(Double) Math.PI Math.Cos(Double) ULong - ULong ULong * ULong ULong << ULong List.OrderBy(Of Double)(Func) Hmm... Is it possible that OrderBy is using a non-stable QuickSort and that QuickSort is using a random pivot? Edit: Just tested, nope. The sort is stable.

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• Swap bits in c++ for a double

  - by hidayat

  Im trying to change from big endian to little endian on a double. One way to go is to use double val, tmp = 5.55; ((unsigned int *)&val)[0] = ntohl(((unsigned int *)&tmp)[1]); ((unsigned int *)&val)[1] = ntohl(((unsigned int *)&tmp)[0]); But then I get a warning: "dereferencing type-punned pointer will break strict-aliasing rules" and I dont want to turn this warning off. Another way to go is: #define ntohll(x) ( ( (uint64_t)(ntohl( (uint32_t)((x << 32) >> 32) )) << 32) | ntohl( ((uint32_t)(x >> 32)) ) ) val = (double)bswap_64(unsigned long long(tmp)); //or val = (double)ntohll(unsigned long long(tmp)); But then a lose the decimals. Anyone know a good way to swap the bits on a double without using a for loop?

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• round number in JavaScript to N decimal places

  - by Richard

  in JavaScript, the typical way to round a number to N decimal places is something like: function round_number(num, dec) { return Math.round(num * Math.pow(10, dec)) / Math.pow(10, dec); } However this approach will round to a maximum of N decimal places while I want to always round to N decimal places. For example "2.0" would be rounded to "2". Any ideas?

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• XMLSerialization Floating Point Accuracy

  - by Steven

  Is it guaranteed that the binary representation of singles, doubles, and floats will be identical to the original after serializing and deserializing?

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• Why is my number being rounded incorrectly?

  - by izb

  This feels like the kind of code that only fails in-situ, but I will attempt to adapt it into a code snippet that represents what I'm seeing. float f = myFloat * myConstInt; /* Where myFloat==13.45, and myConstInt==20 */ int i = (int)f; int i2 = (int)(myFloat * myConstInt); After stepping through the code, i==269, and i2==268. What's going on here to account for the difference?

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