I already have an A* Implementation that works. The problem is that if you pick a destination that is unwalkable, no path is returned. I want to be able to get the 'closest' I can get.
The preferable option would be completely dynamic (not just checking the 8 tiles around the destination to try to find one). That way, even if they click an unwalkable tile surrounded by a huge square of unwalkable tiles, it will still get as close as it can.
While the simple answers provided here MIGHT be sufficient enough, I think it depends on your game type and what you're trying to achieve.
For example, take this play field (sorry I'm reusing the same software I used to show you the fog of war :)) :
As you can see, an Angry Chicken is blocking the path between the left side and the right side. The Angry Chicken could be anything... if it's a static obstacle, then going with the lowest h node might be enough, but if it's a dynamic object (like a locked door, draw bridge, etc...) the following examples might help you find out how you want to solve your problem.
If we set the destination for our Hero on the other side
We need to think what we want the path to be, since obviously we can't reach it. Using a standard heuristic like manhattan distance or euclidian distance, you will get this result:
Which might be good enough, but if there's any way our little Hero could interact with the chicken to pass, it doesn't make sense at all, what you want is this
How can you do this? Well, an easy way to do this is to pathfind on hierarchical graphs. This sounds complicated but it isn't. First, you want to be able to build a new set of high level nodes and edges that will contain multiple grid nodes (or other representation, wouldn't change a thing)
As you can see, we now have a right blue node and a left red node. The arrow represents the edge between the two nodes. How to build this graph you ask? It's easy, simply start from an open node, expand all of its neighbors and add them to a high level node, when you're done, open the dynamic nodes that could lead to another part of the graph and do the same.
Now, when you ask for a path from our Hero to the red X, you first do the pathfinding on the high level... is there a way from blue node to red node? Yes! Through the chicken.
You can now easily know how to navigate on the blue side by going to the edge that will allow you to cross, which is the chicken.
If it was just a plain wall, you could determine very quickly, by visiting a single node, that there is NO way to reach on the other side and then handle it the way you want, possibly still performing an A* and returning the lowest h node.
You could keep a pointer which holds a tile with the lowest h-value, then if no path is returned simply generate a path to the tile you're holding onto instead.
Related
Description:
The goal of my current project is to determine the location of an "object" with just its 3D-coordinates.
To achieve that I figured it'd be best to turn off the "Fill"-Mode of my Camera (ZED 2 from Stereolabs), because I want some hard edges in my depth-image.
The Problem:
The depth image is being distorted to a major degree due to proximity of other "objects".
The following image shows the depth image from the side, it is viewing some bars before a smooth woodwall. The wall is mostly plain, so everything is fine here.
I blacked the Color-Image and Myself, do not worry about those parts.
When I put my hand or another object in front of the wood wall parts that are bigger than my actual hand get "pulled" towards the camera around the location of the hand or other object. These parts seem to "stick" to other elevated parts in the proximity, as the area between the bars and my arm gets pulled entirely.
Question(s):
Is this normal?
Is there an easy way to get rid of it?
What is the reason behind it?
My own assumption(s):
Feel like this is some sort of approximation of unknown parts
Hopefully.. Glad the camera was calibrated by default, as that usually is a pain to do right.
Due to the new object that gets put in front of the wall, there is more stuff hidden and therefore more areas that the camera cannot see with both lenses, maybe it just "guesses" that the area between is not so far off due to some underlying algorithms that make the image smoother..
First of all I would advice you to change the depth mode also with keeping the sensing mode in STANDARD:
ULTRA: offers the highest depth range and better preserves Z-accuracy along the sensing range.
QUALITY: has a strong filtering stage giving smooth surfaces.
PERFORMANCE: designed to be smooth, can miss some details.
*********************From your description, it seems like you are using the Performance mode
The ZED Camera uses a matching alogorithm to generate the disparity/depth map, which is a closed source and I have recently contacted stereolabs about that and they've said "We cannot disclose this information to you because it's internal information and proprietary to Stereolabs."
Other works on the zed camera showed some limitations in depth sensing, specially when there is a variation in lightning and shadows. """Depth Data Error Modeling of the ZED 3D Vision Sensor from
Stereolabs"""
In addition to this, the depth error is directly proportional to the distance of the object from the camera, so make sure to set your depth range properly.
I´m creating a 2D isometric city building simulation and today I have kind of a "best practice" question without asking for specific code.
As in all city building games you are able to place building, roads and so on. The player is able to place building everywhere, no matter if it´s connected to a road or not. In addition to that there is one building (call it center building) all the buildings need to be connected with (by road).
I need to handle that without doing too many calculations which, breaks the FPS.
Right now I have a timer job for each building which checks if one of the surrounded tiles of a building is a road. That works fine, also for a lot of buildings since the check is simple.
But now I would like to check the connection to the center building. To check that it is necessary (in my opinion) to use something like a pathfinder, which checks if one of the surrounded tiles has a road connection to one of the surrounded tiles of the center building.
I can not check that frequently because this completely smashes the FPS down to 30 or lower. My idea was to fire an event if a road has been built or destroyed to "recalulate" the road connection. But there comes another problem...the player might destoy a road in the middle of the map and the buildings are really far away from each other so I need to find the involved buildings which also might take too much time.
My last idea is creating something like a timer queue and work through these items gradually, but before I keep using the trial and error method I would like to ask you for ideas.
Really looking forward to your ideas!
Yheeky
You could have each building store a list of tiles (a path) that connects it to the center building. Then when a tile is randomly destroyed by the player, you can have each building tested to see if it pathed through that road tile or not.
Alternatively you could have each road tile store which buildings require it, so when the tile is destroyed you have the buildings immediately throw flags. This could get quite messy though, but lends itself decently to background speed cleanup calls.
Both methods are quite messy. Perhaps you can make it a rule that the player can't place roads except next to other roads or next to the center building. Then when the player deletes a road tile, do a paint-style fill that destroys all of the disconnected roads. You can also periodically do a random check on tiles to see if they are illegally placed or not, but that should be unnecessary if you're careful.
I'm working on a game (using Game Maker: Studio Professional v1.99.355) that needs to have both user-modifiable level geometry and AI pathfinding based on platformer physics. Because of this, I need a way to dynamically figure out which platforms can be reached from which other platforms in order to build a node graph I can feed to A*.
My current approach is, more or less, this:
For each platform consider each other platform in the level.
For each of those platforms, if it is obviously unreachable (due to being higher than the maximum jump height, for example) do not form a link and move on to next platform.
If a link seems possible, place an ai_character instance on the starting platform and (within the current step event) simulate a jump attempt.
3.a Repeat this jump attempt for each possible starting position on the starting platform.
If this attempt is successful, record the data necessary to replicate it in real time and move on to the next platform.
If not, do not form a link.
Repeat for all platforms.
This approach works, more or less, and produces a link structure that when visualised looks like this:
linked platforms (Hyperlink because no rep.)
In this example the mostly-concealed pink ghost in the lower right corner is trying to reach the black and white box. The light blue rectangles are just there to highlight where recognised platforms are, the actual platforms are the rows of grey boxes. Link lines are green at the origin and red at the destination.
The huge, glaring problem with this approach is that for a level of only 17 platforms (as shown above) it takes over a second to generate the node graph. The reason for this is obvious, the yellow text in the screen centre shows us how long it took to build the graph: over 24,000(!) simulated frames, each with attendant collision checks against every block - I literally just run the character's step event in a while loop so everything it would normally do to handle platformer movement in a frame it now does 24,000 times.
This is, clearly, unacceptable. If it scales this badly at a mere 17 platforms then it'll be a joke at the hundreds I need to support. Heck, at this geometric time cost it might take years.
In an effort to speed things up, I've focused on the other important debugging number, the tests counter: 239. If I simply tried every possible combination of starting and destination platforms, I would need to run 17 * 16 = 272 tests. By figuring out various ways to predict whether a jump is impossible I have managed to lower the number of expensive tests run by a whopping 33 (12%!). However the more exceptions and special cases I add to the code the more convinced I am that the actual problem is in the jump simulation code, which brings me at long last to my question:
How would you determine, with complete reliability, whether it is possible for a character to jump from one platform to another, preferably without needing to simulate the whole jump?
My specific platform physics:
Jumps are fixed height, unless you hit a ceiling.
Horizontal movement has no acceleration or inertia.
Horizontal air control is allowed.
Further info:
I found this video, which describes a similar problem but which doesn't provide a good solution. This is literally the only resource I've found.
You could limit the amount of comparisons by only comparing nearby platforms. I would probably only check the horizontal distance between platforms, and if it is wider than the longest jump possible, then don't bother checking for a link between those two. But you might have done this since you checked for the max height of a jump.
I glanced at the video and it gave me an idea. Instead of looking at all platforms to find which jumps are impossible, what if you did the opposite? Try placing an AI character on all platforms and see which other platforms they can reach. That's certainly easier to implement if your enemies can't change direction in midair though. Oh well, brainstorming is the key to finding something.
Several ideas you could try out:
Limit the amount of comparisons you need to make by using a spatial data structure, like a quad tree. This would allow you to severely limit how many platforms you're even trying to check. This is mostly the same as what you're currently doing, but a bit more generic.
Try to pre-compute some jump trajectories ahead of time. This will not catch all use cases that you have - as you allow for full horizontal control - but might allow you to catch some common cases more quickly
Consider some kind of walkability grid instead of a link generation scheme. When geometry is modified, compute which parts of the level are walkable and which are not, with some resolution (something similar to the dimensions of your agent might be good starting point). You could also filter them with a height, so that grid tiles that are higher than your jump height, and you can't drop from a higher place on to them, are marked as unwalkable. Then, when you compute your pathfinding, as part of your pathfinding step you can compute when you start a jump, if a path is actually executable ('start a jump, I can go vertically no more than 5 tiles, and after the peak of the jump, i always fall down vertically with some speed).
I want to create a simple game with a space ship that needs to dodge asteroids and stuff along the way.
Now, I can think of several ways to spawn the obstacles in the map. My only problem is, how do I implement the idea of an endless map/scrollable map?
For instance, in Flappy Bird there is an endless map.
I just want to know what is the best approach to implement this kind of thing.
Like Alon said, for the background you can use several horizontally "tileable" textures, just load them behind the current one when it's edge is almost visible. You can actually make multiple layers to create depth, for instance you can create a foreground layer with some clouds/nebula's the player travels behind, then some space dust behind the player traveling slower and some planets traveling very slowly in the distance.
Simply create a array for each layer of tileable background textures. Make these textures a bit (or a lot) wider then the actual screen. Keep adding textures to the right side, pick them randomly from your array, and let them scroll. Of course you delete textures when they traversed the screen and not shown anymore.
For your objects you just spawn the asteroids off screen and let them travel across the screen. You maintain a asteroid list and each time you need an asteroid you generate it with a random Y axis and add it to the list. When you need to draw or calculate collision you traverse this list and do your stuff on each asteroid.
There are many ways to do it. I recommend this one:
Move your character in needed direction and respawn obstacles on global position. Camera should follow the character. For moving background you have two options: ParallaxBackground which already knows how to move backgrounds or you can just create two backgrounds and when character will be in the end of first one you will move second background to the end.
This has been greatly bothering me in the past few weeks. In this time I've been researching online, even reading books in the Computers section at Borders to try to find an answer, but I haven't had much luck.
I programmed a 2D level editor for side-scroller video games. Now I want to turn it into a game where I have a player who can run and jump to explore the level, similar to "Mario".
The thing that is really giving me trouble is the collision response (not detection: I already know how to tell if two blocks are colliding). Here are some scenarios that I am going to illustrate so that you can see my problems (the shaded blocks are the ground, the arrow is the velocity vector of the player, the dashed lines are the projected path of the player).
See this collision response scenarios image:
http://dl.dropbox.com/u/12556943/collision_detection.jpg
Assume that the velocity vectors in scenarios (1) and (2) are equal (same direction and magnitude). Yet, in scenario (1), the player is hitting the side of the block, and in scenario (2), the player is landing on top of the block. This allows me to conclude that determining the collision response is dependent not only on the velocity vector of the player, but also the player's relative position to the colliding block. This leads to my first question: knowing the velocity vector and the relative position of the player, how can I determine from which direction (either left side, right side, top, or bottom) the player is colliding with the block?
Another problem that I'm having is how to determine the collision response if the player collides with multiple blocks in the same frame. For instance, assume that in scenario (3), the player collides with both of those blocks at the same time. I'm assuming that I'm going to have to loop through each block that the player is colliding with and adjust the reaction accordingly from each block. To sum it up, this is my second question: how do I handle collision response if the player collides with multiple blocks?
Notice that I never revealed the language that I'm programming in; this is because I'd prefer for you to not know (nothing personal, though :] ). I'm more interested in pseudo-code than to see language-specific code.
Thanks!
I think the way XNA's example platform game handles collisions could work well for you. I posted this answer to a very similar question elsewhere on Stack Overflow but will relay it here as well.
After applying movement, check for and resolve collisions.
Determine the tiles the player overlaps based on the player's bounding box.
Iterate through all of those tiles doing the following: (it's usually not very many unless your player is huge compared to your world tiles)
If the tile being checked isn't passable:
Determine how far on the X and Y axes the player is overlapping the non-passable tile
Resolve collision by moving the player out of that tile only on the shallow axis (whichever axis is least penetrated)
For example, if Y is the shallow axis and the collision is below, shift the player up to no longer overlap that tile.
Something like this: if(abs(overlap.y) < abs(overlap.x)) { position.y += overlap.y; } else { position.x += overlap.x; }
Update the bounding box's position based on the player's new position
Move on to the next tile...
If the tile being checked is passable, do nothing
If it's possible that resolving a collision could move the player into another collision, you may want to run through the above algorithm a second time. Or redesign your level.
The XNA version of this logic is in player.cs in the HandleCollisions() function if you are interested in grabbing their code to see what they specifically do there.
So what makes this a little more tricky is the constant force of gravity adjusting your players position. If your player jumps on top of a block they shouldn't bounce off they should land on top of the block and stay there. However, if the player hits a block on the left or right they shouldn't just stay there gravity must pull them down. I think that's roughly your question at a high level.
I think you'll want to separate the two forces of gravity and player velocity from collision detection/response algorithm. Using the velocity of the player if they collide with a block regardless of direction simply move the player's position to the edge of the collision, and subtract equal and opposite vector from the player's velocity since not doing this would cause them to collide yet again with the object. You will want to calculate the intersection point and place the player's position there on the block.
On a side note you could vary that really big force by what type of block the player collided with allowing for interesting responses like the player can break through the block if they are running fast enough (ie the player's velocity > than the force of the block)
Then continue to apply the constant force gravity to the player's position and continue doing your normal calculation to determine if the player has reached a floor.
I think by separating these two concepts you have a really simple straight forward collision response algorithm, and you have a fairly simple gravity-floor algorithm. That way you can vary gravity without having to redo your collision response algorithm. Say for example a water level, space level, etc and collision detection response is all the same.
I thought about this for a long time recently.
I am using the separating axis theorem, and so if I detected a collision I proceeded to project the object onto the normalized velocity vector and move the object by that distance in the direction of the negative velocity vector. Assuming the object came from a safe place this solution will position the object in a safe place post collision.
May not be the answer you're looking to get, but hopefully it'll point you in the right direction?