So I've very recently got started with programming due to one of the subjects I have at class. So far the most complex thing we've learned are loops, we know if, while and for SO I have to manage with that.
In this exercise, program asks for the price of whatever you bought and the money spent. We have unlimited coins of value 50 20 10 5 2 and 1. If you spent more than it costs, the program will give you the change.
Example:
Price?: 44.
Money Paid?: 100.
Change is 56: 50 5 1.
I've tried making it simpler so that I can jump into the whole thing after understanding it.
My logic here was trying to make a similar program but using one coin only.
int change, payment, price;
if (payment == price)
{
Console.Write("\nNo change needed, you paid with the exact value.\n");
}
else if (payment < price)
{
Console.Write("\nNot enough money.\n");
}
else {
Console.Write("Change is {0}: ", change);
for (loop100 = 0; loop100 < change; loop100+=100)
{
if (change > 100)
{
Console.Write(100 + (" "));
}
}
}
Program prints
Price?: 1000 /*lets say 1000*/
Payment?: 1500
Change is 500: 100 100 100 100 100
Now, on paper this is what I am looking for. But the issue comes when setting another for loop with a different value. If I copy my for/if loop but changing loop100 for lets say a loop50and setting it up for a 50 value coin, first of all, it goes on a endless loop of 50s, and secondly I wouldnt get the most efficient combination of 100+50 coins but the change with each type of coin. I'd get 100- 5 times and 50- 10 times.
I've put literally hours into this problem and I can't solve it. I looked online and everyone seems to do it with Arrays but my teacher does not want us to use Arrays as we havent learned yet about those and it is much more simple than that.
What kind of for loop should I try? Did I make it too much harder than it already is?
My personal preference is to use a while loop for this. Inside that you can use an embedded if statement or for loop to move through a range of coins values:
/// <summary>
/// Ouput the change from the paid amount for the specified price.
/// </summary>
/// <param name="price">An int indicating the price of the purchase.</param>
/// <param name="paid">An int indicating the total amount paid.</param>
private static void outputChange(int price, int paid)
{
int change = paid - price;
int[] coins = new[] { 50, 20, 10, 5, 2, 1 };
if (change > 0)
{
Console.Write("Change: ");
while (change > 0)
{
for (int i = 0; i < coins.Length; i++)
{
if (change >= coins[i])
{
Console.Write($"{coins[i]} ");
change -= coins[i];
break;
}
}
}
Console.Write("\n");
}
else
Console.WriteLine("No change needed, you paid with the exact value.");
}
This works by finding the next coin that is larger than or equal to the remaining change, and then subtracting that value from change. The while loop will continue until change is 0 (or below, which is not expected).
Examples:
outputChange(44, 100);
outputChange(23, 100);
outputChange(86, 100);
outputChange(100, 100);
Output:
Change: 50 5 1
Change: 50 20 5 2
Change: 10 2 2
No change needed, you paid with the exact value.
Edit following OP comment
OP added a comment stating that they would prefer not to use an array for the coins:
Could the same while+for statement be used by creating a value for
every single type of coin? I really have to avoid using arrays for now
In this case, another (less elegant) method could use an if statement that calculated the next coin, see below:
/// <summary>
/// Ouput the change from the paid amount for the specified price.
/// </summary>
/// <param name="price">An int indicating the price of the purchase.</param>
/// <param name="paid">An int indicating the total amount paid.</param>
private static void outputChange(int price, int paid)
{
int change = paid - price;
if (change > 0)
{
Console.Write("Change: ");
while (change > 0)
{
int coin = 0;
if (change >= 50)
coin = 50;
else if (change >= 20)
coin = 20;
else if (change >= 10)
coin = 10;
else if (change >= 5)
coin = 5;
else if (change >= 2)
coin = 2;
else if (change >= 1)
coin = 1;
if (coin > 0)
{
Console.Write($"{coin} ");
change -= coin;
}
else
break;
}
Console.Write("\n");
}
else
Console.WriteLine("No change needed, you paid with the exact value.");
}
While loop would probably work better. Keep track of how much change is left to deliver.
while( change >= 100)
{
change -= 100;
Console.Write(100 + (" "));
}
while( change >= 50)
{
change -= 50;
Console.Write(50 + (" "));
}
I'm trying to build a heart rate monitor, which I intend to code a mobile application around. Currently, I'm receiving the data in my application. Heres an example of the data:
However, I really would like to be able to remove the static element below the pulsating curve through some sort of high pass filter. Currently, I have the following code:
//HIGH PASS
//Fetch the next measurement item
j = float.Parse(Encoding.Default.GetString(e.Characteristic.Value));
counter++;
total += j;
if (counter % 5 == 0)
{
avg = total / counter;
total = 0;
counter = 0;
}
if (j < h || h > avg && h >= 0)
{
h = j;
}
else if (h <= 0) //Initially h is 0
{
h = j;
}
float g = j-(h-5); //This is the output
The code does to some degree work. What it does, is that it monitors the data and sets h=j if a lower value is present (by doing so, I constantly have the lowest point on the curve, which I can then remove).
Furthermore, for every 5 data points, a new average is put. Primarily to constantly check whether the filter is set too high. (i have roughly 6 data points every second)
The code is not really optimal. One of the major flaws is, if I remove my finger from the Heart rate sensor (j is being significantly lower), meaning that the curve will have almost no HR sine curve.
I could potentially add h=avg; to the counter if-statement. But that would cause the curve to constantly flicker up and down.
What are your suggestion guys? how can I tweak this?
I am writing a simple game where animations are done using a timer. Timer rate is initially set to 200, but for every 1000 points player gets I want timer to get faster, so I thought I could just decrease the interval
if (score > 0 && score % 1000 == 0)
{
GameTimer.Interval -= 20;
}
But when I reach score of 1000, winform crashes with following error on the line given above:
System.ArgumentOutOfRangeException: 'Value '0' is not a valid value for Interval. Interval must be greater than 0.
Parameter name: Interval
How can I correctly reduce the interval rate? (or make my program tick faster by any other means)
Edit: The code piece given above was placed inside the tick event, which caused if statement to execute several times
The error indicates that the Interval value has reached zero.
So these lines are executed several times until it crashes:
if (score > 0 && score % 1000 == 0)
{
GameTimer.Interval -= 20;
}
And that is because the condition is met in every interval after the timer passes the condition once.
Define your logic outside the timer code and you'll be fine:
void Score(int value){
score += value;
if (score <= 0) return;
if(score % 1000 == 0)
{
GameTimer.Interval -= 20;
//if(GameTimer.Interval <= 0) I suppose level is already finished...
}
}
edited
mjwills pointed out this issue that the interval still may hit zero. So you must write your code in a manner that eliminates this risk.
a non-linear reduction makes more sense in this case:
void Score(int value){
score += value;
if (score <= 0) return;
if(score % 1000 == 0)
{
GameTimer.Interval *= .9f;
if(GameTimer.Interval <= 0) GameTimer.Interval = 1;
}
}
The tick rate cannot be less than or equal to 0.
You could simply add an if statement to check that:
if (GameTimer.Interval <= 20) {
GameTimer.Interval = 1;
} else {
GameTimer.Interval -= 20;
}
However, this means that the timer interval will reach a limit after a certain score is reached. Also, the screen can't update that fast (1000 times a second). You should probably keep the frame rate at 30fps.
Therefore, to make the animation appear faster, do a larger proportion of the animation in each second. For example, to move something 1000 pixels to the right, don't move it 1 pixel every 1/1000 of a second. Instead, move it 50 pixels every 1/20 of a second.
From your comment:
The issue is that I do not understand why interval is going below zero, the if statement is executed only once, and it immediately gives me that error.
Then you are executing the if statement more than once. My guess is that you are running it in the timer tick event handler. Once your score reaches a multiple of 1000, that if statement will be run every time the timer ticks, until your score changes.
To fix this, you can put the code in the setter of the score.
the timer interval keep decrease until it reach to zero "0" that is your error
you can use
int x = (score/1000)*20
if (x < 200)
GameTimer.Interval = (200 - x);
I'm making a game with a score text and was wondering how I would write a script that doubles the points added to the score if some condition happens twice in a row? So far, I have a block that adds 2 points instead of 1 if the player gets the bullet in a certain region. The code is as follows:
if (-0.02f < transform.forward.x && transform.forward.x < 0.03f) {
perfectScoreText.GetComponent<Animator> ().Play ("PerfectHit");
currentScore += 2;
scoreText.text = "" + currentScore;
}
I was wondering how I'd make that code add two times as much as the user completes the condition twice/thrice/etc in a row.
Thanks.
Add a counter for perfect hit. Lets say perfectHitCounter. When perfect hit occurs increase this counter by one, if perfect hit fails make this counter zero. And when it reaches 2, add double score and reset the counter or if your game has the combo system you can increase the counter till you miss the perfect shot.
PSEUDO
I assume the code you provide is where the perfect hit happens.
if (-0.02f < transform.forward.x && transform.forward.x < 0.03f) //Perfect Hit
{
//Perfect hit
perfectHitCounter += 1;
//Add normal score if you wish
}
if('not perfect score condition')
{
perfectHitCounter = 0;
}
if(perfectHitCounter >= 2)
{
currentScore += 2;
//perfectHitCounter = 0; //If there is no combo system.
}
Hope this helps. Cheers!
I'm working on a simple demo for collision detection, which contains only a bunch of objects bouncing around in the window. (The goal is to see how many objects the game can handle at once without dropping frames.)
There is gravity, so the objects are either moving or else colliding with a wall.
The naive solution was O(n^2):
foreach Collidable c1:
foreach Collidable c2:
checkCollision(c1, c2);
This is pretty bad. So I set up CollisionCell objects, which maintain information about a portion of the screen. The idea is that each Collidable only needs to check for the other objects in its cell. With 60 px by 60 px cells, this yields almost a 10x improvement, but I'd like to push it further.
A profiler has revealed that the the code spends 50% of its time in the function each cell uses to get its contents. Here it is:
// all the objects in this cell
public ICollection<GameObject> Containing
{
get
{
ICollection<GameObject> containing = new HashSet<GameObject>();
foreach (GameObject obj in engine.GameObjects) {
// 20% of processor time spent in this conditional
if (obj.Position.X >= bounds.X &&
obj.Position.X < bounds.X + bounds.Width &&
obj.Position.Y >= bounds.Y &&
obj.Position.Y < bounds.Y + bounds.Height) {
containing.Add(obj);
}
}
return containing;
}
}
Of that 20% of the program's time is spent in that conditional.
Here is where the above function gets called:
// Get a list of lists of cell contents
List<List<GameObject>> cellContentsSet = cellManager.getCellContents();
// foreach item, only check items in the same cell
foreach (List<GameObject> cellMembers in cellContentsSet) {
foreach (GameObject item in cellMembers) {
// process collisions
}
}
//...
// Gets a list of list of cell contents (each sub list = 1 cell)
internal List<List<GameObject>> getCellContents() {
List<List<GameObject>> result = new List<List<GameObject>>();
foreach (CollisionCell cell in cellSet) {
result.Add(new List<GameObject>(cell.Containing.ToArray()));
}
return result;
}
Right now, I have to iterate over every cell - even empty ones. Perhaps this could be improved on somehow, but I'm not sure how to verify that a cell is empty without looking at it somehow. (Maybe I could implement something like sleeping objects, in some physics engines, where if an object will be still for a while it goes to sleep and is not included in calculations for every frame.)
What can I do to optimize this? (Also, I'm new to C# - are there any other glaring stylistic errors?)
When the game starts lagging out, the objects tend to be packed fairly tightly, so there's not that much motion going on. Perhaps I can take advantage of this somehow, writing a function to see if, given an object's current velocity, it can possibly leave its current cell before the next call to Update()
UPDATE 1 I decided to maintain a list of the objects that were found to be in the cell at last update, and check those first to see if they were still in the cell. Also, I maintained an area of the CollisionCell variable, when when the cell was filled I could stop looking. Here is my implementation of that, and it made the whole demo much slower:
// all the objects in this cell
private ICollection<GameObject> prevContaining;
private ICollection<GameObject> containing;
internal ICollection<GameObject> Containing {
get {
return containing;
}
}
/**
* To ensure that `containing` and `prevContaining` are up to date, this MUST be called once per Update() loop in which it is used.
* What is a good way to enforce this?
*/
public void updateContaining()
{
ICollection<GameObject> result = new HashSet<GameObject>();
uint area = checked((uint) bounds.Width * (uint) bounds.Height); // the area of this cell
// first, try to fill up this cell with objects that were in it previously
ICollection<GameObject>[] toSearch = new ICollection<GameObject>[] { prevContaining, engine.GameObjects };
foreach (ICollection<GameObject> potentiallyContained in toSearch) {
if (area > 0) { // redundant, but faster?
foreach (GameObject obj in potentiallyContained) {
if (obj.Position.X >= bounds.X &&
obj.Position.X < bounds.X + bounds.Width &&
obj.Position.Y >= bounds.Y &&
obj.Position.Y < bounds.Y + bounds.Height) {
result.Add(obj);
area -= checked((uint) Math.Pow(obj.Radius, 2)); // assuming objects are square
if (area <= 0) {
break;
}
}
}
}
}
prevContaining = containing;
containing = result;
}
UPDATE 2 I abandoned that last approach. Now I'm trying to maintain a pool of collidables (orphans), and remove objects from them when I find a cell that contains them:
internal List<List<GameObject>> getCellContents() {
List<GameObject> orphans = new List<GameObject>(engine.GameObjects);
List<List<GameObject>> result = new List<List<GameObject>>();
foreach (CollisionCell cell in cellSet) {
cell.updateContaining(ref orphans); // this call will alter orphans!
result.Add(new List<GameObject>(cell.Containing));
if (orphans.Count == 0) {
break;
}
}
return result;
}
// `orphans` is a list of GameObjects that do not yet have a cell
public void updateContaining(ref List<GameObject> orphans) {
ICollection<GameObject> result = new HashSet<GameObject>();
for (int i = 0; i < orphans.Count; i++) {
// 20% of processor time spent in this conditional
if (orphans[i].Position.X >= bounds.X &&
orphans[i].Position.X < bounds.X + bounds.Width &&
orphans[i].Position.Y >= bounds.Y &&
orphans[i].Position.Y < bounds.Y + bounds.Height) {
result.Add(orphans[i]);
orphans.RemoveAt(i);
}
}
containing = result;
}
This only yields a marginal improvement, not the 2x or 3x I'm looking for.
UPDATE 3 Again I abandoned the above approaches, and decided to let each object maintain its current cell:
private CollisionCell currCell;
internal CollisionCell CurrCell {
get {
return currCell;
}
set {
currCell = value;
}
}
This value gets updated:
// Run 1 cycle of this object
public virtual void Run()
{
position += velocity;
parent.CellManager.updateContainingCell(this);
}
CellManager code:
private IDictionary<Vector2, CollisionCell> cellCoords = new Dictionary<Vector2, CollisionCell>();
internal void updateContainingCell(GameObject gameObject) {
CollisionCell currCell = findContainingCell(gameObject);
gameObject.CurrCell = currCell;
if (currCell != null) {
currCell.Containing.Add(gameObject);
}
}
// null if no such cell exists
private CollisionCell findContainingCell(GameObject gameObject) {
if (gameObject.Position.X > GameEngine.GameWidth
|| gameObject.Position.X < 0
|| gameObject.Position.Y > GameEngine.GameHeight
|| gameObject.Position.Y < 0) {
return null;
}
// we'll need to be able to access these outside of the loops
uint minWidth = 0;
uint minHeight = 0;
for (minWidth = 0; minWidth + cellWidth < gameObject.Position.X; minWidth += cellWidth) ;
for (minHeight = 0; minHeight + cellHeight < gameObject.Position.Y; minHeight += cellHeight) ;
CollisionCell currCell = cellCoords[new Vector2(minWidth, minHeight)];
// Make sure `currCell` actually contains gameObject
Debug.Assert(gameObject.Position.X >= currCell.Bounds.X && gameObject.Position.X <= currCell.Bounds.Width + currCell.Bounds.X,
String.Format("{0} should be between lower bound {1} and upper bound {2}", gameObject.Position.X, currCell.Bounds.X, currCell.Bounds.X + currCell.Bounds.Width));
Debug.Assert(gameObject.Position.Y >= currCell.Bounds.Y && gameObject.Position.Y <= currCell.Bounds.Height + currCell.Bounds.Y,
String.Format("{0} should be between lower bound {1} and upper bound {2}", gameObject.Position.Y, currCell.Bounds.Y, currCell.Bounds.Y + currCell.Bounds.Height));
return currCell;
}
I thought this would make it better - now I only have to iterate over collidables, not all collidables * cells. Instead, the game is now hideously slow, delivering only 1/10th of its performance with my above approaches.
The profiler indicates that a different method is now the main hot spot, and the time to get neighbors for an object is trivially short. That method didn't change from before, so perhaps I'm calling it WAY more than I used to...
It spends 50% of its time in that function because you call that function a lot. Optimizing that one function will only yield incremental improvements to performance.
Alternatively, just call the function less!
You've already started down that path by setting up a spatial partitioning scheme (lookup Quadtrees to see a more advanced form of your technique).
A second approach is to break your N*N loop into an incremental form and to use a CPU budget.
You can allocate a CPU budget for each of the modules that want action during frame times (during Updates). Collision is one of these modules, AI might be another.
Let's say you want to run your game at 60 fps. This means you have about 1/60 s = 0.0167 s of CPU time to burn between frames. No we can split those 0.0167 s between our modules. Let's give collision 30% of the budget: 0.005 s.
Now your collision algorithm knows that it can only spend 0.005 s working. So if it runs out of time, it will need to postpone some tasks for later - you will make the algorithm incremental. Code for achieving this can be as simple as:
const double CollisionBudget = 0.005;
Collision[] _allPossibleCollisions;
int _lastCheckedCollision;
void HandleCollisions() {
var startTime = HighPerformanceCounter.Now;
if (_allPossibleCollisions == null ||
_lastCheckedCollision >= _allPossibleCollisions.Length) {
// Start a new series
_allPossibleCollisions = GenerateAllPossibleCollisions();
_lastCheckedCollision = 0;
}
for (var i=_lastCheckedCollision; i<_allPossibleCollisions.Length; i++) {
// Don't go over the budget
if (HighPerformanceCount.Now - startTime > CollisionBudget) {
break;
}
_lastCheckedCollision = i;
if (CheckCollision(_allPossibleCollisions[i])) {
HandleCollision(_allPossibleCollisions[i]);
}
}
}
There, now it doesn't matter how fast the collision code is, it will be done as quickly as is possible without affecting the user's perceived performance.
Benefits include:
The algorithm is designed to run out of time, it just resumes on the next frame, so you don't have to worry about this particular edge case.
CPU budgeting becomes more and more important as the number of advanced/time consuming algorithms increases. Think AI. So it's a good idea to implement such a system early on.
Human response time is less than 30 Hz, your frame loop is running at 60 Hz. That gives the algorithm 30 frames to complete its work, so it's OK that it doesn't finish its work.
Doing it this way gives stable, data-independent frame rates.
It still benefits from performance optimizations to the collision algorithm itself.
Collision algorithms are designed to track down the "sub frame" in which collisions happened. That is, you will never be so lucky as to catch a collision just as it happens - thinking you're doing so is lying to yourself.
I can help here; i wrote my own collision detection as an experiment. I think i can tell you right now that you won't get the performance you need without changing algorithms. Sure, the naive way is nice, but only works for so many items before collapsing. What you need is Sweep and prune. The basic idea goes like this (from my collision detection library project):
using System.Collections.Generic;
using AtomPhysics.Interfaces;
namespace AtomPhysics.Collisions
{
public class SweepAndPruneBroadPhase : IBroadPhaseCollider
{
private INarrowPhaseCollider _narrowPhase;
private AtomPhysicsSim _sim;
private List<Extent> _xAxisExtents = new List<Extent>();
private List<Extent> _yAxisExtents = new List<Extent>();
private Extent e1;
public SweepAndPruneBroadPhase(INarrowPhaseCollider narrowPhase)
{
_narrowPhase = narrowPhase;
}
public AtomPhysicsSim Sim
{
get { return _sim; }
set { _sim = null; }
}
public INarrowPhaseCollider NarrowPhase
{
get { return _narrowPhase; }
set { _narrowPhase = value; }
}
public bool NeedsNotification { get { return true; } }
public void Add(Nucleus nucleus)
{
Extent xStartExtent = new Extent(nucleus, ExtentType.Start);
Extent xEndExtent = new Extent(nucleus, ExtentType.End);
_xAxisExtents.Add(xStartExtent);
_xAxisExtents.Add(xEndExtent);
Extent yStartExtent = new Extent(nucleus, ExtentType.Start);
Extent yEndExtent = new Extent(nucleus, ExtentType.End);
_yAxisExtents.Add(yStartExtent);
_yAxisExtents.Add(yEndExtent);
}
public void Remove(Nucleus nucleus)
{
foreach (Extent e in _xAxisExtents)
{
if (e.Nucleus == nucleus)
{
_xAxisExtents.Remove(e);
}
}
foreach (Extent e in _yAxisExtents)
{
if (e.Nucleus == nucleus)
{
_yAxisExtents.Remove(e);
}
}
}
public void Update()
{
_xAxisExtents.InsertionSort(comparisonMethodX);
_yAxisExtents.InsertionSort(comparisonMethodY);
for (int i = 0; i < _xAxisExtents.Count; i++)
{
e1 = _xAxisExtents[i];
if (e1.Type == ExtentType.Start)
{
HashSet<Extent> potentialCollisionsX = new HashSet<Extent>();
for (int j = i + 1; j < _xAxisExtents.Count && _xAxisExtents[j].Nucleus.ID != e1.Nucleus.ID; j++)
{
potentialCollisionsX.Add(_xAxisExtents[j]);
}
HashSet<Extent> potentialCollisionsY = new HashSet<Extent>();
for (int j = i + 1; j < _yAxisExtents.Count && _yAxisExtents[j].Nucleus.ID != e1.Nucleus.ID; j++)
{
potentialCollisionsY.Add(_yAxisExtents[j]);
}
List<Extent> probableCollisions = new List<Extent>();
foreach (Extent e in potentialCollisionsX)
{
if (potentialCollisionsY.Contains(e) && !probableCollisions.Contains(e) && e.Nucleus.ID != e1.Nucleus.ID)
{
probableCollisions.Add(e);
}
}
foreach (Extent e2 in probableCollisions)
{
if (e1.Nucleus.DNCList.Contains(e2.Nucleus) || e2.Nucleus.DNCList.Contains(e1.Nucleus))
continue;
NarrowPhase.DoCollision(e1.Nucleus, e2.Nucleus);
}
}
}
}
private bool comparisonMethodX(Extent e1, Extent e2)
{
float e1PositionX = e1.Nucleus.NonLinearSpace != null ? e1.Nucleus.NonLinearPosition.X : e1.Nucleus.Position.X;
float e2PositionX = e2.Nucleus.NonLinearSpace != null ? e2.Nucleus.NonLinearPosition.X : e2.Nucleus.Position.X;
e1PositionX += (e1.Type == ExtentType.Start) ? -e1.Nucleus.Radius : e1.Nucleus.Radius;
e2PositionX += (e2.Type == ExtentType.Start) ? -e2.Nucleus.Radius : e2.Nucleus.Radius;
return e1PositionX < e2PositionX;
}
private bool comparisonMethodY(Extent e1, Extent e2)
{
float e1PositionY = e1.Nucleus.NonLinearSpace != null ? e1.Nucleus.NonLinearPosition.Y : e1.Nucleus.Position.Y;
float e2PositionY = e2.Nucleus.NonLinearSpace != null ? e2.Nucleus.NonLinearPosition.Y : e2.Nucleus.Position.Y;
e1PositionY += (e1.Type == ExtentType.Start) ? -e1.Nucleus.Radius : e1.Nucleus.Radius;
e2PositionY += (e2.Type == ExtentType.Start) ? -e2.Nucleus.Radius : e2.Nucleus.Radius;
return e1PositionY < e2PositionY;
}
private enum ExtentType { Start, End }
private sealed class Extent
{
private ExtentType _type;
public ExtentType Type
{
get
{
return _type;
}
set
{
_type = value;
_hashcode = 23;
_hashcode *= 17 + Nucleus.GetHashCode();
}
}
private Nucleus _nucleus;
public Nucleus Nucleus
{
get
{
return _nucleus;
}
set
{
_nucleus = value;
_hashcode = 23;
_hashcode *= 17 + Nucleus.GetHashCode();
}
}
private int _hashcode;
public Extent(Nucleus nucleus, ExtentType type)
{
Nucleus = nucleus;
Type = type;
_hashcode = 23;
_hashcode *= 17 + Nucleus.GetHashCode();
}
public override bool Equals(object obj)
{
return Equals(obj as Extent);
}
public bool Equals(Extent extent)
{
if (this.Nucleus == extent.Nucleus)
{
return true;
}
return false;
}
public override int GetHashCode()
{
return _hashcode;
}
}
}
}
and here's the code that does the insertion sort (more-or-less a direct translation of the pseudocode here):
/// <summary>
/// Performs an insertion sort on the list.
/// </summary>
/// <typeparam name="T">The type of the list supplied.</typeparam>
/// <param name="list">the list to sort.</param>
/// <param name="comparison">the method for comparison of two elements.</param>
/// <returns></returns>
public static void InsertionSort<T>(this IList<T> list, Func<T, T, bool> comparison)
{
for (int i = 2; i < list.Count; i++)
{
for (int j = i; j > 1 && comparison(list[j], list[j - 1]); j--)
{
T tempItem = list[j];
list.RemoveAt(j);
list.Insert(j - 1, tempItem);
}
}
}
IIRC, i was able to get an extremely large performance increase with that, especially when dealing with large numbers of colliding bodies. You'll need to adapt it for your code, but that's the basic premise behind sweep and prune.
The other thing i want to remind you is that you should use a profiler, like the one made by Red Gate. There's a free trial which should last you long enough.
It looks like you are looping through all the game objects just to see what objects are contained in a cell. It seems like a better approach would be to store the list of game objects that are in a cell for each cell. If you do that and each object knows what cells it is in, then moving objects between cells should be easy. This seems like it will yield the biggest performance gain.
Here is another optimization tip for determing what cells an object is in:
If you have already determined what cell(s) an object is in and know that based on the objects velocity it will not change cells for the current frame, there is no need to rerun the logic that determines what cells the object is in. You can do a quick check by creating a bounding box that contains all the cells that the object is in. You can then create a bounding box that is the size of the object + the velocity of the object for the current frame. If the cell bounding box contains the object + velocity bounding box, no further checks need to be done. If the object isn't moving, it's even easier and you can just use the object bounding box.
Let me know if that makes sense, or google / bing search for "Quad Tree", or if you don't mind using open source code, check out this awesome physics library: http://www.codeplex.com/FarseerPhysics
I'm in the exact same boat as you. I'm trying to create an overhead shooter and need to push efficiency to the max so I can have tons of bullets and enemies on screen at once.
I'd get all of my collidable objects in an array with a numbered index. This affords the opportunity to take advantage of an observation: if you iterate over the list fully for each item you'll be duplicating efforts. That is (and note, I'm making up variables names just to make it easier to spit out some pseudo-code)
if (objs[49].Intersects(objs[51]))
is equivalent to:
if (objs[51].Intersects(objs[49]))
So if you use a numbered index you can save some time by not duplicating efforts. Do this instead:
for (int i1 = 0; i1 < collidables.Count; i1++)
{
//By setting i2 = i1 + 1 you ensure an obj isn't checking collision with itself, and that objects already checked against i1 aren't checked again. For instance, collidables[4] doesn't need to check against collidables[0] again since this was checked earlier.
for (int i2 = i1 + 1; i2 < collidables.Count; i2++)
{
//Check collisions here
}
}
Also, I'd have each cell either have a count or a flag to determine if you even need to check for collisions. If a certain flag is set, or if the count is less than 2, than no need to check for collisions.
Just a heads up: Some people suggest farseer; which is a great 2D physics library for use with XNA. If you're in the market for a 3D physics engine for XNA, I've used bulletx (a c# port of bullet) in XNA projects to great effect.
Note: I have no affiliation to the bullet or bulletx projects.
An idea might be to use a bounding circle. Basically, when a Collidable is created, keep track of it's centre point and calculate a radius/diameter that contains the whole object. You can then do a first pass elimination using something like;
int r = C1.BoundingRadius + C2.BoundingRadius;
if( Math.Abs(C1.X - C2.X) > r && Math.Abs(C1.Y - C2.Y) > r )
/// Skip further checks...
This drops the comparisons to two for most objects, but how much this will gain you I'm not sure...profile!
There are a couple of things that could be done to speed up the process... but as far as I can see your method of checking for simple rectangular collision is just fine.
But I'd replace the check
if (obj.Position.X ....)
With
if (obj.Bounds.IntersercsWith(this.Bounds))
And I'd also replace the line
result.Add(new List<GameObject>(cell.Containing.ToArray()));
For
result.Add(new List<GameObject>(cell.Containing));
As the Containing property returns an ICollection<T> and that inherits the IEnumerable<T> that is accepted by the List<T> constructor.
And the method ToArray() simply iterates to the list returning an array, and this process is done again when creating the new list.
I know this Thread is old but i would say that the marked answar was completly wrong...
his code contain a fatal error and don´t give performance improvent´s it will take performence!
At first a little notic...
His code is created so that you have to call this code in your Draw methode but this is the wrong place for collision-detection. In your draw methode you should only draw nothing else!
But you can´t call HandleCollisions() in Update, because Update get a lots of more calls than Draw´s.
If you want call HandleCollisions() your code have to look like this... This code will prevent that your collision detection run more then once per frame.
private bool check = false;
protected override Update(GameTime gameTime)
{
if(!check)
{
check = true;
HandleCollisions();
}
}
protected override Draw(GameTime gameTime)
{
check = false;
}
Now let us take a look what´s wrong with HandleCollisions().
Example: We have 500 objects and we would do a check for every possible Collision without optimizing our detection.
With 500 object we should have 249500 collision checks (499X500 because we don´t want to check if an object collide with it´s self)
But with Frank´s code below we will lose 99.998% of your collosions (only 500 collision-checks will done). << THIS WILL INCREASE THE PERFORMENCES!
Why? Because _lastCheckedCollision will never be the same or greater then allPossibleCollisions.Length... and because of that you would only check the last index 499
for (var i=_lastCheckedCollision; i<_allPossibleCollisions.Length; i++)
_lastCheckedCollision = i;
//<< This could not be the same as _allPossibleCollisions.Length,
//because i have to be lower as _allPossibleCollisions.Length
you have to replace This
if (_allPossibleCollisions == null ||
_lastCheckedCollision >= _allPossibleCollisions.Length)
with this
if (_allPossibleCollisions == null ||
_lastCheckedCollision >= _allPossibleCollisions.Length - 1) {
so your whole code can be replaced by this.
private bool check = false;
protected override Update(GameTime gameTime)
{
if(!check)
{
check = true;
_allPossibleCollisions = GenerateAllPossibleCollisions();
for(int i=0; i < _allPossibleCollisions.Length; i++)
{
if (CheckCollision(_allPossibleCollisions[i]))
{
//Collision!
}
}
}
}
protected override Draw(GameTime gameTime)
{
check = false;
}
... this should be a lot of faster than your code ... and it works :D ...
RCIX answer should marked as correct because Frank´s answar is wrong.