i always use the contact listener in this way :
b2Body *bodyA=contact.fixtureA->GetBody();
b2Body *bodyB=contact.fixtureB->GetBody();
.
.
CCSprite *actora = (CCSprite*)bodyA->GetUserData();
CCSprite *actorb = (CCSprite*)bodyB->GetUserData();
.
.
if ([actora tag] == 6 && ( [actorb tag]== 4 || [actorb tag]== 5 ) ) // question !!
//do stuff here
now i find my self always try to guess who is actora and who is b.
lets say that some body is flying and hit another body. sometimes the hitten body is a and the other one is b and vise versa.
i dont want to check all conditions, and want to know whats the algorithm to know that .
i was thinking that the first body on screen gets the a (first defined sprite) .
that was right, till i found it wrong :)
so , how would i know a/b who is which ? (is it random ?? )
thanks a lot.
See all body in space is linked through a linked list and you have to travel the list to get the required element, it's not like a array through which we can select any element without traveling the list.
So, In our case this is a linked list and we have to travel through the link path and we don't know which body we will get first So we have to examine both condition. No other way to find that.
So it looks random :-)
It's all is linked list.
Thanks
Related
I have an assignment for my class where we are attempting to find the best (cheapest) path to a destination. The description is as follows:
Each tech has a name, a cost to buy that tech, a boolean saying whether or not the player has the tech already, and a list of 0 to N techs that are available for purchase when the player buys this tech. There are three categories of tech in Tactigo: Social, Military, and Science. Each of the three starts with a basic tech that the player must purchase before purchasing more advanced techs. These basic techs are special because they are always available for purchase.
Looking at the diagram, you will note that a few techs are unlocked by multiple techs. Remember that techs are unlocked as soon as ANY tech unlocks them. In other words, you need either "Being Nice to Animals" OR "Being a Dick to People" in order to buy "Attack Animal Training". You don't need both, just one. Your task is to find the cheapest way to get any given technology. The player might own any set of techs already, so you must account for that. For example, if the player already owns "Being Nice to People" and wants to find the cheapest way to get "Making Friends", the path returned should just be "Making Friends". They don't need to purchase anything else.
The Graph looks as follows:
I originally thought of doing a depth-first-search on each of the 3 categories while calculating the cost of each path taken. My Code for this function is as follows:
//---------------------------------------------------------------------------------------------------------------------
// This function finds the best path to the tech we want.
// * goalTech: The index of the tech we're looking for. Call GetTechByIndex() to get the actual Tech instance.
// * bestPath: The best path to the goal tech. This is an array sorted in the order of the best path from the
// start to the goal. This is an output variable; it's what you need to populate with this function.
//---------------------------------------------------------------------------------------------------------------------
void TechTree::FindBestPath(int goalTech, Path& bestPath)
{
//First ensure that best path is cleared out
bestPath.clear();
//Get Tech Instance for this Goal Tech
const Tech* pGoalTech = GetTechByIndex(goalTech);
//make sure we get a valid tech
assert(pGoalTech != nullptr);
//Check first if user already has this unlocked.
if (pGoalTech->HasTech())
{
//just return
return;
}
//Check if the goal tech is one of the three starting techs.
if (pGoalTech == GetBasicSocialTech()|| pGoalTech == GetBasicScienceTech() || pGoalTech == GetBasicMilitaryTech())
{
//now we know that one of the basic techs are the goal, so we just add one of those to the path
if (pGoalTech == GetBasicSocialTech())
bestPath.push_back(GetBasicSocialTech());
else if (pGoalTech == GetBasicMilitaryTech())
bestPath.push_back(GetBasicMilitaryTech());
else
bestPath.push_back(GetBasicScienceTech());
return; //now return
}
//my process will be as follows.
//1. Since all the edges are directed we need to traverse down three different graphs: Social (starting at index 0), Military (starting at index 4) and Science (starting at index 8)
//2. I am going to perform a depth-first search starting at Social and then moving down to Military and then Science.
//3. As I am performing a depth-first I am going to keep track of a path and its respective cost, if a search gets to the goal I will make sure to register that and then move onto the next graph.
//4. When there are no more paths to search I send the lowest cost one back.
///start with social at index 0
const Tech* pStartSocialTech = GetBasicSocialTech();
std::pair<int, std::vector<const Tech*>> bestCurrentPath;
//get starting cost for this category before we move into neighbors,
// if player already has this tech we set this to zero if not we get the cost of buying into this category
int startingCost = pStartSocialTech->HasTech() ? 0 : pStartSocialTech->GetCost();
/*pStartSocialNeighbors = get all neighbors for starting point at social
while (destination is not found AND there are more neighbors to pStartSocialNeighbors)
{
DFS(neighbor, dest) //if this finds the destination we store a path and its cost, otherwise it doesnt do anything and we move on to next basic tree
}
//do the same thing for military and science...
*/
}
I have a lot of comments on it but I am just wondering if this is the best route to take. Other options are Dijkstras or A* but I don't know how you would traverse the path of this directed graph. I am not looking for a direct answer since this is a homework assignment but I am looking for some guidance.
Thanks!
Going from the target to source using Dijkstras, you need to modify the stop condition if you want to stop before searching all paths. I don't see any heuristic for A* in this case.
Adding a node with a path to all known techs
You can now use Dijkstras / Bellman-Ford.
Using A* has the problem you need to find a heuristic that works. You could use depth times min cost of all edges. that requires you to already have traversed the graph to assign depth.
I am trying to code a gui that is dynamically assigned. I have four teams. I am getting stuck at a certain point. I want to make a function that, when a player joins the game, checks if the other teams have already scored to update their labels. It looks like this:
local function updateAllLabelsLateArrival(redPoints, bluePoints, yellowPoints, greenPoints)
game.Players.LocalPlayer.PlayerGui.ScreenGui.ReallyRedTeam.Points.Text = redPoints
game.Players.LocalPlayer.PlayerGui.ScreenGui.ReallyBlueTeam.Points.Text = bluePoints
game.Players.LocalPlayer.PlayerGui.ScreenGui.NewYellerTeam.Points.Text = yellowPoints
game.Players.LocalPlayer.PlayerGui.ScreenGui.LimeGreenTeam.Points.Text = greenPoints
end
The function is remotely triggered from a server-side script when a player joins. The problem I have is that not all four labels might exist. Suppose a green team player joins in when there is only a red team player already playing. It will come back with the error
ReallyBlueTeam is not a valid member of ScreenGui
I thought wrapping each line in an if statement to check if the label exists, like so:
if game.Players.LocalPlayer.PlayerGui.ScreenGui.ReallyRedTeam then game.Players.LocalPlayer.PlayerGui.ScreenGui.ReallyRedTeam.Points.Text = redPoints end
But this is giving the same error. So my question is, how do I check that a label has been created before updating the points? thanks
Assuming this is a localcsript, you can use WaitForChild() which will yield until the label has been created!
game.Players.LocalPlayer.PlayerGui:WaitForChild("ScreenGui"):WaitForChild("ReallyRedTeam"):WaitForChild("Points").Text = redPoints
More information about WaitForChild here!
Alternatively, if you don't know for definite they will be created, you can use FindFirstChild. This won't yield.
if game.Players.LocalPlayer.PlayerGui.ScreenGui:FindFirstChild("ReallyRedTeam") then
print("it exists")
end
More information about FindFirstChild here!
Hope that helps!
If you want them all on one line each then the best to use would be FindFirstChild() as #jjwood1600 has said. I would also recommend making use of a variable to shorten your GUI paths as you can see below:
local function updateAllLabelsLateArrival(redPoints, bluePoints, yellowPoints, greenPoints)
local userGui = game.Players.LocalPlayer.PlayerGui.ScreenGui
if userGui:FindFirstChild("ReallyRedTeam") then userGui.ReallyRedTeam.Points.Text = redPoints end
if userGui:FindFirstChild("ReallyBlueTeam") then userGui.ReallyBlueTeam.Points.Text = bluePoints end
if userGui:FindFirstChild("NewYellerTeam") then userGui.NewYellerTeam.Points.Text = yellowPoints end
if userGui:FindFirstChild("LimeGreenTeam") then userGui.LimeGreenTeam.Points.Text = greenPoints end
end
In normal Lua you can indeed do the if statements the way you did where you don't use FindFirstChild but Roblox's own version RBX.Lua doesn't.
New to Go and building a simple LRU cache in Go to get used to syntax and Go development.
Having an issue with the MoveToFront list method, it fails on the following check in the MoveToFront body
if e.list != l || l.root.next == e
I want to move the element (e) to the front of the list when I retrieve it from cache , like this
if elem, ok := lc.entries[k]; ok {
lc.list.MoveToFront(elem) // needs fixing
return elem
}
return nil
The Code can be seen here on line 32 the issue occurs
https://github.com/hajjboy95/golrucache/blob/master/lru_cache/lrucache.go#L32
There seem to be two problems, to me. First, this isn't how the List data type is meant to be used: lc.list.PushFront() will create a List.Element and return a pointer to it. That's not fatal, but at the least, it is kind of annoying—the caller has to dig through the returned List.Element when using Get, instead of just getting the value.
Meanwhile, presumably the failure you see is because you remove elements in Put when the LRU-list runs out of space, but you don't remove them from the corresponding map. Hence a later Put of the just-removed key will try to re-use the element in place, even though the element was removed from the list. To fix this, you'll need to hold both key and value. (In my simple experiment I did not see any failures here, but the problem became clear enough.)
I restructured the code somewhat and turned it into a working example on the Go Playground. I make no promises as to suitability, etc.
I've searched my best on here in order to find the answer to my question but there's either no results or I'm not searching the right thing, but anyway...
The battleships game I need to create has to have: 1 Aircraft Carrier of length 5, 2 battleships of length 4, 3 destroyers of length 3 and 4 submarines of length 2.
I have a ship class which holds data such as the id, name, x, y and direction.
I then have a board class which then needs to instantiate all these ships. I'm doing this by making a vector of type Ship and pushing ship objects onto that.
However each ship objects needs to store all the x and y values of that ship and I'm stuck on how to do that. I wanted to post code but it's non functional and looks messy at the moment which is probably not beneficial to anyone. However if necessary I can write the skeleton again and post it up here.
Thanks in advance.
If you have x, y and direction then the points of the ship can be calculated from it's size
Each ship could just have a vector<Point> inside. Checking for hit could be then:
Point guess;
for (auto& ship : ships) {
for (auto& point : ship.points) {
if (point == guess)
// hit
}
}
That would make sense if you are aiming for a version where you need to hit the ship once in each of its parts.
The inner loop can also be easily changed to std::find, making it arguably more clear.
I'm not getting any error messages, simply my vector is not populating. Looking at the vector in the watch list, nothing is being copied. Why is this?
I've tried two ways.
The first
std::vector<Point3D*> hitpoints;
local_hit_point = sr.local_hit_point; //local_hit_point class Point3D
hitpoints.push_back(local_hit_point);
The second way I tried to use pointers
std::vector<Point3D*> hitpoints;
Point3D* hittingpoint_ptr = new Point3D;
local_hit_point = sr.local_hit_point;
hittingpoint_ptr = &local_hit_point;
hitpoints.push_back(hittingpoint_ptr);
I got vectors in other places in my code which work. Am I really just being daft, but I can't seem to figure out why its not working.
My best guess is that you have an issue with you debugger..
First Suggestion;
Clear everything in your watchlist because they can change the behaviour of the execution
check it again..
Second suggestion;
Create a new project and write a simple code like the one above and see whether your vector is populating..If this simple project works, you should provide us more code and details..
simply my vector is not populating.
It is populating. However
Looking at the vector in the watch list ...
I used hitpoint.size()
Results of function/method calls (size() is a method) are not automatically updated in visual studio watch list (because you haven't told what os/compiler you use I had to assume it is visual studio). I.e. if you enter function call into watch list, it'll calculate results, but will not call function again until you manually refresh it. Instead of function call, add vector itself into watch list.