Develop Reference

Randomly generate blocks on a flat map

I'm trying to randomly generate blocks on a flat map and make it so that they don't overlap each other.
I have made a matrix (c# array) of the size of the map (500x500), the blocks have a scale between 1 and 5.
The code works but if a generated block overlaps another one, it is destroyed and not regenerated somewhere else.
Only around 80 of the 1000 blocks I try to generate don't overlap another block.
Here is a picture of the map with around 80 blocks generated, the green squares are blocks
void generateElement(int ratio, int minScale, int maxScale, GameObject g) {
bool elementFound = false;
for (int i = 0; i < ratio * generationDefault; i++) {
GameObject el;
// Randomly generate block size and position
int size = Random.Range(minScale, maxScale + 1);
int x = Random.Range(0, mapSizex + 1 - size);
int y = Random.Range(0, mapSizey + 1 - size);
// Check if there is already an element
for (int j = x; j < x + size; j++)
for (int k = y; k < y + size; k++)
if (map[j][k] != null)
elementFound = true;
if (elementFound)
continue;
else {
el = (GameObject)Instantiate(g, new Vector3(x + (float)size / 2, (float)size / 2, y + (float)size / 2), Quaternion.Euler(0, 0, 0));
el.transform.localScale *= size;
}
// Create element on map array
for (int j = x; j < x + size; j++)
for (int k = y; k < y + size; k++)
if (map[j][k] == null) {
map[j][k] = el.GetComponent<ObjectInterface>();
}
}
}
I thought of 3 possible fixes
I should set the size of the block depending of the place it has.
I should use another randomization algorithm.
I'm not doing this right.
What do you think is the best idea ?
UPDATE
I got the code working much better. I now try to instantiate the blocks multiple times if needed (maximum 5 for the moment) and I fixed the bugs. If there are already many elements on the map, they will not always be instantiated and that's what I wanted, I just have to find the right amount of times it will try to instantiate the block.
I tried instantiating 1280 elements on a 500x500 map. It takes only about 1.5 second and it instantiated 1278/1280 blocks (99.843%).
void generateElement(int ratio, int minScale, int maxScale, GameObject g) {
bool elementFound = false;
int cnt = 0;
// Generate every block
for (int i = 0; i < ratio * generationDefault; i++) {
GameObject el = null;
// Randomly generate block size and position
int size, x, y, tryCnt = 0;
// Try maximum 5 times to generate the block
do {
elementFound = false;
// Randomly set block size and position
size = Random.Range(minScale, maxScale + 1);
x = Random.Range(0, mapSizex + 1 - size);
y = Random.Range(0, mapSizey + 1 - size);
// Check if there is already an element
for (int j = x; j < x + size; j++)
for (int k = y; k < y + size; k++)
if (map[j][k] != null)
elementFound = true;
tryCnt++;
} while (elementFound && tryCnt < 5);
if (tryCnt >= 5 && elementFound) continue;
// Instantiate the block
el = (GameObject)Instantiate(g, new Vector3(x + (float)size / 2, (float)size / 2, y + (float)size / 2), Quaternion.Euler(0, 0, 0));
el.transform.localScale *= size;
// Create element on map array
for (int j = x; j < x + size; j++)
for (int k = y; k < y + size; k++)
if (map[j][k] == null) {
map[j][k] = el.GetComponent<ObjectInterface>();
}
cnt++;
}
print("Instantiated " + cnt + "/" + ratio * generationDefault);
}

This is incredibly difficult to do well.
Here's a quick solution you'll maybe like ... depending on your scene.
actualWidth = 500 //or whatever. assume here is square
// your blocks are up to 5 size
chunkWidth = actualWidth / 5
// it goes without saying, everything here is an int
kChunks = chunkWidth*chunkWidth
List<int> shuf = Enumerable.Range(1,kChunks).OrderBy(r=>Random.value).ToList();
howManyWanted = 1000
shuf = shuf.Take(howManyWanted)
foreach( i in shuf )
x = i % actualWidth
y = i / actualWidth
make block at x y
put block in list allBlocks
HOWEVER ............
...... you'll see that this looks kind of "regular", so do this:
Just randomly perturb all the blocks. Remember, video game programming is about clever tricks!
Ideally, you have to start from the middle and work your way out; in any event you can't just do them in a line. Shuffling is OK. So, do this ..
harmonic = 3 //for example. TRY DIFFERENT VALUES
function rh = Random.Range(1,harmonic) (that's 1 not 0)
function rhPosNeg
n = rh
n = either +n or -n
return n
function onePerturbation
{
allBlocks = allBlocks.OrderBy(r => Random.value) //essential
foreach b in allBlocks
newPotentialPosition = Vector2(rhPosNeg,rhPosNeg)
possible = your function to check if it is possible
to have a block at newPotentialPosition,
however be careful not to check "yourself"
if possible, move block to newPotentialPosition
}
The simplest approach is just run onePerturbation, say, three times. Have a look at it between each run. Also try different values of the harmonic tuning factor.
There are many ways to perturb fields of differently-sized blocks, above is a KISS solution that hopefully looks good for your situation.
Coding note...
How to get sets of unique random numbers.
Just to explain this line of code...
List<int> shuf = Enumerable.Range(1,kChunks).OrderBy(r=>Random.value).ToList();
If you are new to coding: say you want to do this: "get a hundred random numbers, from 1 to million, but with no repeats".
Fortunately, this is a very well known problem with a very simple solution.
The way you get numbers with no repeats, is simply shuffle all the numbers, and then take how many you want off the top.
For example, say you need a random couple of numbers from 1-10 but with no repeats.
So, here's the numbers 1-10 shuffled: 3,8,6,1,2,7,10,9,4,5
Simply take what you need off the front: so, 3, 8, 6 etc.
So to make an example let's say you want twelve numbers, no repeats, from 1 through 75. So the first problem is, you want a List with all the numbers up to 75, but shuffled. In fact you do that like this ..
List<int> shuf = Enumerable.Range(1,75).OrderBy(r=>Random.value).ToList();
So that list is 75 items long. You can check it by saying foreach(int r in shuf) Debug.Log(r);. Next in the example you only want 12 of those numbers. Fortunately there's a List call that does this:
shuf = shuf.Take(12)
So, that's it - you now have 12 numbers, no repeats, all random between 1 and 75. Again you can check with foreach(int r in shuf) Debug.Log(r);
In short, when you want "n" numbers, no repeats, between 1 and Max, all you have to so is this:
List<int> shuf = Enumerable.Range(1,Max).OrderBy(r=>Random.value).ToList();
shuf = shuf.Take(n);
et voilà, you can check the result with foreach(int r in shuf) Debug.Log(r);
I just explain this at length because the question is often asked "how to get random numbers that are unique". This is an "age-old" programming trick and the answer is simply that you shuffle an array of all the integers involved.
Interestingly, if you google this question ("how to get random numbers that are unique") it's one of those rare occasions where google is not much help, because: whenever this question is asked, you get a plethora of keen new programmers (who have not heard the simple trick to do it properly!!) writing out huge long complicated ideas, leading to further confusion and complication.
So that's how you make random numbers with no repeats, fortunately it is trivial.

if (elementFound) continue; will skip out this current loop iteration. You need to wrap the int x=Random..; int y=Random()..; part in a while loop with the condition being while(/* position x/y already occupued*/) { /* generate new valid point */} like this for example:
void generateElement(int ratio, int minScale, int maxScale, GameObject g) {
for (int i = 0; i < ratio * generationDefault; i++) {
GameObject el;
// Randomly generate block size and position
bool elementFound = false;
int size, x, y;
do
{
elementFound = false;
size = Random.Range(minScale, maxScale + 1);
x = Random.Range(0, mapSizex + 1 - size);
y = Random.Range(0, mapSizey + 1 - size);
// Check if there is already an element
for (int j = x; j < x + size; j++)
for (int k = y; k < y + size; k++)
if (map[j][k] != null)
elementFound = true;
} while(elementFound);
el = (GameObject)Instantiate(g, new Vector3(x + (float)size / 2, (float)size / 2, y + (float)size / 2), Quaternion.Euler(0, 0, 0));
el.transform.localScale *= size;
// Create element on map array
for (int j = x; j < x + size; j++)
for (int k = y; k < y + size; k++)
if (map[j][k] == null) {
map[j][k] = el.GetComponent<ObjectInterface>();
}
}
}

You shouldn't be getting that many collisions.
Assuming your blocks were ALL 5 units wide and you're trying to fit them into a grid of 500,500 you would have 100*100 spaces for them at minimum, which gives 10,000 spaces into which to fit 1,000 blocks.
Try playing around with this code:
using System;
using System.Collections.Generic;
namespace ConsoleApplication1
{
class Program
{
static void Main()
{
var result = PlaceNonOverlappingBlocks(1000, 5, 500, 500);
}
static List<Block> PlaceNonOverlappingBlocks(int count, int maxBlockSize, int mapX, int mapY)
{
var map = new bool[mapY, mapX];
var rng = new Random();
var result = new List<Block>(count);
int collisions = 0;
while (count > 0)
{
int size = rng.Next(1, maxBlockSize + 1);
int x = rng.Next(0, mapX - size);
int y = rng.Next(0, mapY - size);
if (fits(map, x, y, size))
{
result.Add(new Block(x, y, size));
addToMap(map, x, y, size);
--count;
}
else
{
if (++collisions> 100000)
throw new InvalidOperationException("Hell has frozen over");
}
}
// This is just for diagnostics, and can be removed.
Console.WriteLine($"There were {collisions} collisions.");
return result;
}
static void addToMap(bool[,] map, int px, int py, int size)
{
for (int x = px; x < px+size; ++x)
for (int y = py; y < py + size; ++y)
map[y, x] = true;
}
static bool fits(bool[,] map, int px, int py, int size)
{
for (int x = px; x < px + size; ++x)
for (int y = py; y < py + size; ++y)
if (map[y, x])
return false;
return true;
}
internal class Block
{
public int X { get; }
public int Y { get; }
public int Size { get; }
public Block(int x, int y, int size)
{
X = x;
Y = y;
Size = size;
}
}
}
}

C# Exp cannot get result

When I using Math.Exp() in C# I have some questions?This code is about Kernel density estimation, and I don't have any knowledge about kernel density estimation. So I look up some wiki and some paper.
I try to write it by C#. The problem is when "distance" is getting higher the result is become 0. It's confuse me and I cannot find any other way to get the right result.
disExp = Math.Pow(Math.E, -(distance / 2 * Math.Pow(h, 2)));
So, can any one help me to get the solution? Or give me some idea about Kernel density estimation on C#. Sorry for poor English.

Try this
public static double[,] KernelDensityEstimation(double[] data, double sigma, int nsteps)
{
// probability density function (PDF) signal analysis
// Works like ksdensity in mathlab.
// KDE performs kernel density estimation (KDE)on one - dimensional data
// http://en.wikipedia.org/wiki/Kernel_density_estimation
// Input: -data: input data, one-dimensional
// -sigma: bandwidth(sometimes called "h")
// -nsteps: optional number of abscis points.If nsteps is an
// array, the abscis points will be taken directly from it. (default 100)
// Output: -x: equispaced abscis points
// -y: estimates of p(x)
// This function is part of the Kernel Methods Toolbox(KMBOX) for MATLAB.
// http://sourceforge.net/p/kmbox
// Converted to C# code by ksandric
double[,] result = new double[nsteps, 2];
double[] x = new double[nsteps], y = new double[nsteps];
double MAX = Double.MinValue, MIN = Double.MaxValue;
int N = data.Length; // number of data points
// Find MIN MAX values in data
for (int i = 0; i < N; i++)
{
if (MAX < data[i])
{
MAX = data[i];
}
if (MIN > data[i])
{
MIN = data[i];
}
}
// Like MATLAB linspace(MIN, MAX, nsteps);
x[0] = MIN;
for (int i = 1; i < nsteps; i++)
{
x[i] = x[i - 1] + ((MAX - MIN) / nsteps);
}
// kernel density estimation
double c = 1.0 / (Math.Sqrt(2 * Math.PI * sigma * sigma));
for (int i = 0; i < N; i++)
{
for (int j = 0; j < nsteps; j++)
{
y[j] = y[j] + 1.0 / N * c * Math.Exp(-(data[i] - x[j]) * (data[i] - x[j]) / (2 * sigma * sigma));
}
}
// compilation of the X,Y to result. Good for creating plot(x, y)
for (int i = 0; i < nsteps; i++)
{
result[i, 0] = x[i];
result[i, 1] = y[i];
}
return result;
}
kernel density estimation C#
plot

Image processing task: Erosion C#

I am doing an image processing assignment where I want to implement erosion and dilation algorithm. It needs to look for each pixel in all directions (in this case up, down, left and right), so i'm using a plus structuring element. Here is my problem: I've got 4 for loops nested, which makes this operation very slow.
Can anyone tell me how to make the erosion process quicker without using unsafe method?
Here is what I have:
colorlistErosion = new List<Color>();
int colorValueR, colorValueG, colorValueB;
int tel = 0;
for (int y = 0; y < bitmap.Height; y++)
{
for (int x = 0; x < bitmap.Width; x++)
{
Color col = bitmap.GetPixel(x, y);
colorValueR = col.R; colorValueG = col.G; colorValueB = col.B;
//Erosion
for (int a = -1; a < 2; a++)
{
for (int b = -1; b < 2; b++)
{
try
{
Color col2 = bitmap.GetPixel(x + a, y + b);
colorValueR = Math.Min(colorValueR, col2.R);
colorValueG = Math.Min(colorValueG, col2.G);
colorValueB = Math.Min(colorValueB, col2.B);
}
catch
{
}
}
}
colorlistErosion.Add(Color.FromArgb(0 + colorValueR, 0+colorValueG, 0+colorValueB));
}
}
for (int een = 0; een < bitmap.Height; een++)
for (int twee = 0; twee < bitmap.Width; twee++)
{
bitmap.SetPixel(twee, een, colorlistErosion[tel]);
tel++;
}

how to make the erosion process quicker without using unsafe method?
You can turn the inner loops into Parallel.For().
But I'm not 100% sure if GetPixel() and especially SetPixel() are thread-safe. That is a deal-breaker.

Your algorithm is inherently slow due to the 4 nested loops. You're also processing the bitmap using the slowest approach possible bitmap.GetPixel.
Take a look at SharpGL. If they don't have your filters you can download the source code and figure out how to make your own.

finding maximum in a 3d matrix

I have matrix with 3 dimension (n*m*k). I am trying to fined the maximum number for each n and m by searching in k dimension.((I try to find the maximum number in k dimension for each n and m)) and at last i have a 2d matrix (n*m). i have the following code but it is so slow. Is there any new code or any changes to the current code that do this more quickly.
thanks.
my c# code: note: li is the 3 dimension matrix and they are grater or equal to zero.
int[,] array2 = new int[n, m];
int[,] array = new int[n, m];
List<Array> li = new List<Array>();
for(int k = 0; k <'not a specific value, change each time' ; k++)
{
li.Add(array);
%% changing array
} %% so li will became a (n*m*k) matrix
for (int i = 0; i < n; i++)
for (int j = 0; j < m; j++)
{
int ma = -2;
int d = 0;
while (d <= k)
{
ma = Math.Max(ma, Convert.ToInt32(li[d].GetValue(i, j)));
d++;
}
array2[i, j] = ma;
}

The biggest performance issue is that you use Array objects as elements of your list. This makes it so that every element access using GetValue boxes the value, i.e. allocates a new tiny object to hold the element value.
Your code will run a lot faster if you replace
List<Array> li = new List<Array>();
with
List<int[,]> li = new List<int[,]>();
and
ma = Math.Max(ma, Convert.ToInt32(li[d].GetValue(i, j)));
with
ma = Math.Max(ma, li[d][i, j];
Since you don't know the 3rd dimension in advance, it is harder to use 3D arrays.
An entirely different approach would be to compute the maximum as you're building the list li. This will help in two ways: 1. You avoid indexing into the list of arrays and 2. as long as m and n aren't too large, you improve locality. That is: the values you're working with are closer together in memory, and more likely to be in the processor cache.

This should do the trick (even though it could be kinda slower than your approach):
// put this at the top of your source file
using System.Linq;
// put this where you calculate the maxima
for(int i = 0; i < array2.GetLength(0); ++i)
for(int j = 0; j < array2.GetLength(1); ++j)
{
array2[i, j] = Convert.ToInt32(li.Max(x => x.GetValue(i, j)));
}

You could use a three-dimensional array like this:
int xRange = 10;
int yRange = 10;
int zRange = 10;
int[, ,] matrix = new int[xRange, yRange, zRange];
// set up some dummy values
for (int x = 0; x < xRange; x++)
for (int y = 0; y < yRange; y++)
for (int z = 0; z < zRange; z++)
matrix[x, y, z] = x * y * z;
// calculate maximum values
int[,] maxValues = new int[xRange, yRange];
/* LINQ version of maximum calculation
for (int x = 0; x < xRange; x++)
for (int y = 0; y < yRange; y++)
maxValues[x, y] = Enumerable.Range(0, zRange).Select(z => matrix[x, y, z]).Max();
*/
// longhand version of maximum calculation
for (int x = 0; x < xRange; x++)
for (int y = 0; y < yRange; y++)
for (int z = 0; z < zRange; z++)
maxValues[x, y] = Math.Max(maxValues[x, y], matrix[x, y, z]);
// display results
for (int x = 0; x < xRange; x++)
{
for (int y = 0; y < yRange; y++)
Console.Write("{0}\t", maxValues[x, y]);
Console.WriteLine();
}

From an algorithm perspective, there's no more efficient way to evaluate the maximum value for fixed n,m for all k. It will take O(n*m*k) operations.
Now, the only way to improve performance is to find improvements in your implementation, particularly in your storage of the 3D matrix.
Using List<Array> is a major area for improvement. You are prone to boxing issues (conversion of primitive types to objects) and making more function calls than are necessary.
Reduce your 3D matrix to an array of primitives:
int[] my3DArray = new int[n * m * l]; // Note I'm using l where you use k
Now index into your array at [i, j, k] using the following offset:
int elementAtIJK = my3DArray[i + (n * j) + (m * n * k)];
If you just use arrays of primitives you should see a definite improvement.
Edit:
In fact, in C# (and several other languages) it's very easy to implement 3D arrays directly, e.g.:
int[,,] my3DArray = new int[n,m,l];
int elementAtIJK = my3DArray[i,j,k];
Which is much simpler than I first described (but at the end of the day is internally translated in the 1D form).
What to do if the 3rd dimension varies in size...
Now, it gets more interesting if the size of the 3rd dimension varies significantly. If it has a known maximum and isn't too big, you can simply set it to the maximum and fill the empty values with zeroes. This is simple and may meet your needs.
However, if the 3rd dimension can be very big, all these extra stored zeroes could waste a lot of valuable space and what you need is a Sparse Matrix representation.
There are different storage mechanisms for sparse matrices. For your purposes, you could consider your 3D array to be a 2D matrix, with (n*m) rows and max(k) columns. As the 3rd dimension varies in length, there are lots of empty spaces in your columns. This is called a sparse row and the standard data storage for this is "Compressed Sparse Row". Again, for performance this can be represented just by three primitive arrays, a data array, a row index array and a column pointer array. There are resources elsewhere on the web that describe the CSR implementation better than I can, but hopefully this will point you in the right direction.

Image Comparing and return Percentage

int DiferentPixels = 0;
Bitmap first = new Bitmap("First.jpg");
Bitmap second = new Bitmap("Second.jpg");
Bitmap container = new Bitmap(first.Width, first.Height);
for (int i = 0; i < first.Width; i++)
{
for (int j = 0; j < first.Height; j++)
{
int r1 = second.GetPixel(i, j).R;
int g1 = second.GetPixel(i, j).G;
int b1 = second.GetPixel(i, j).B;
int r2 = first.GetPixel(i, j).R;
int g2 = first.GetPixel(i, j).G;
int b2 = first.GetPixel(i, j).B;
if (r1 != r2 && g1 != g2 && b1 != b2)
{
DiferentPixels++;
container.SetPixel(i, j, Color.Red);
}
else
container.SetPixel(i, j, first.GetPixel(i, j));
}
}
int TotalPixels = first.Width * first.Height;
float dierence = (float)((float)DiferentPixels / (float)TotalPixels);
float percentage = dierence * 100;
With this portion of Code im comparing 2 Images foreach Pixels and yes it work's it return's Percentage of difference ,so it compares each Pixel of First Image with pixel in same index of Second Image .But what is wrong here ,i have a huge precision maybe it should not work like that ,the comparison ,and maybe there are some better algorithms which are faster and more flexible .
So anyone has an idea how can i transform the comparison ,should i continue with that or should i compare Colors of Each Pixels or ....
PS : If anyone has a solution how to make Parallel this code ,i would also accept it ! Like expanding this to 4 Threads would they do it faster right in a Quad Core?

One obvious change would be call GetPixel only once per Bitmap, and then work with the returned Color structs directly:
for (int i = 0; i < first.Width; ++i)
{
for (int j = 0; j < first.Height; ++j)
{
Color secondColor = second.GetPixel(i, j);
Color firstColor = first.GetPixel(i, j);
if (firstColor != secondColor)
{
DiferentPixels++;
container.SetPixel(i, j, Color.Red);
}
else
{
container.SetPixel(i, j, firstColor);
}
}
}

For speed, resize the images to something very small (16x12, for example) and do the pixel comparison. If it is a near match, then try it at higher resolution.