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Programming language: Go
Tags: Game Development    

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README

Tile: Data-Oriented 2D Grid Engine

GitHub go.mod Go version PkgGoDev Go Report Card License Coverage Status

This repository contains a 2D tile map engine which is built with data and cache friendly ways. My main goal here is to provide a simple, high performance library to handle large scale tile maps in games.

  • Compact. Each tile is 6 bytes long and each grid page is 64-bytes long, which means a grid of 3000x3000 should take around 64MB of memory.
  • Thread-safe. The grid is thread-safe and can be updated through provided update function. This allows multiple goroutines to read/write to the grid concurrently without any contentions. There is a spinlock per tile page protecting tile access.
  • Views & observers. When a tile on the grid is updated, viewers of the tile will be notified of the update and can react to the changes. The idea is to allow you to build more complex, reactive systems on top of the grid.
  • Zero-allocation (or close to it) traversal of the grid. The grid is pre-allocated entirely and this library provides a few ways of traversing it.
  • Path-finding. The library provides a A* pathfinding algorithm in order to compute a path between two points, as well as a BFS-based position scanning which searches the map around a point.

Disclaimer: the API or the library is not final and likely to change. Also, since this is just a side project of mine, don't expect this to be updated very often but please contribute!

Grid & Tiles

The main entry in this library is Grid which represents, as the name implies a 2 dimentional grid which is the container of Tile structs. The Tile is basically a byte array [6]byte which allows you to customize what you want to put inside. Granted, it's a bit small but big enough to put an index or two. The reason this is so small is the data layout, which is organised in thread-safe pages of 3x3 tiles, with the total size of 64 bytes which should neatly fit onto a cache line of a CPU.

In order to create a new Grid, you first need to call NewGrid() method which pre-allocates the required space and initializes the tile grid itself. For example, you can create a 1000x1000 grid as shown below.

grid := NewGrid(1000, 1000)

The Each() method of the grid allows you to iterate through all of the tiles in the grid. It takes an iterator function which is then invoked on every tile.

grid.Each(func(p Point, tile Tile) {
    // ...
})

The Within() method of the grid allows you to iterate through a set of tiles within a bounding box, specified by the top-left and bottom-right points. It also takes an iterator function which is then invoked on every tile matching the filter.

grid.Within(At(1, 1), At(5, 5), func(p Point, tile Tile) {
    // ...
})

The At() method of the grid allows you to retrieve a tile at a specific x,y coordinate. It simply returns the tile and whether it was found in the grid or not.

if tile, ok := grid.At(50, 100); ok {
    // ...
}

The WriteAt() method of the grid allows you to update a tile at a specific x,y coordinate. Since the Grid itself is thread-safe, this is the way to (a) make sure the tile update/read is not racing and (b) notify observers of a tile update (more about this below).

grid.WriteAt(50, 100, Tile{1, 2, 3, 4, 5, 6})

The Neighbors() method of the grid allows you to get the direct neighbors at a particular x,y coordinate and it takes an iterator funcion which is called for each neighbor. In this implementation, we are only taking direct neighbors (top, left, bottom, right). You rarely will need to use this method, unless you are rolling out your own pathfinding algorithm.

grid.WriteAt(50, 100, Tile{1, 2, 3, 4, 5, 6})

The MergeAt() method of the grid allows you to transactionally update only some of the bits at a particular x,y coordinate. This operation is as well thread-safe, and is actually useful when you might have multiple goroutines updating a set of tiles, but various goroutines are responsible for the various parts of the tile data. You might have a system that updates only a first couple of tile flags and another system updates some other bits. By using this method, two goroutines can update the different bits of the same tile concurrently, without erasing each other's results, which would happen if you just call WriteAt().

// assume byte[0] of the tile is 0b01010001
grid.MergeAt(0, 0, 
    Tile{0b00101110, 0, 0, 0, 0, 0}, // Only last 2 bits matter
    Tile{0b00000011, 0, 0, 0, 0, 0} // Mask specifies that we want to update last 2 bits
)

// If the original is currently: 0b01010001
// ...the result result will be: 0b01010010

The Neighbors() method of the grid allows you to get the direct neighbors at a particular x,y coordinate and it takes an iterator funcion which is called for each neighbor. In this implementation, we are only taking direct neighbors (top, left, bottom, right). You rarely will need to use this method, unless you are rolling out your own pathfinding algorithm.

grid.WriteAt(50, 100, Tile{1, 2, 3, 4, 5, 6})

Pathfinding

As mentioned in the introduction, this library provides a few grid search / pathfinding functions as well. They are implemented as methods on the same Grid structure as the rest of the functionnality. The main difference is that they may require some allocations (I'll try to minimize it further in the future), and require a cost function func(Tile) uint16 which returns a "cost" of traversing a specific tile. For example if the tile is a "swamp" in your game, it may cost higher than moving on a "plain" tile. If the cost function returns 0, the tile is then considered to be an impassable obstacle, which is a good choice for walls and such.

The Path() method is used for finding a way between 2 points, you provide it the from/to point as well as costing function and it returns the path, calculated cost and whether a path was found or not. Note of caution however, avoid running it between 2 points if no path exists, since it might need to scan the entire map to figure that out with the current implementation.

from := At(1, 1)
goal := At(7, 7)
path, distance, found := m.Path(from, goal, func(t Tile) uint16{
    if isImpassable(t[0]) { 
        return 0
    }
    return 1
})

The Around() method provides you with the ability to do a breadth-first search around a point, by providing a limit distance for the search as well as a cost function and an iterator. This is a handy way of finding things that are around the player in your game.

point  := At(50, 50)
radius := 5
m.Around(point, radius, func(t Tile) uint16{
    if isImpassable(t[0]) { 
        return 0
    }
    return 1
}, func(p Point, t Tile) {
    // ... tile found
})

Observers

Given that the Grid is mutable and you can make changes to it from various goroutines, I have implemented a way to "observe" tile changes through a View() method which creates a View structure and can be used to observe changes within a bounding box. For example, you might want your player to have a view port and be notified if something changes on the map so you can do something about it.

In order to use these observers, you need to first call the View() method and start polling from the Inbox channel which will contain the tile update notifications as they happen. This channel has a small buffer, but if not read it will block the update, so make sure you always poll everything from it.

In the example below we create a new 20x20 view on the grid and iterate through all of the tiles in the view.

view := grid.View(NewRect(0, 0, 20, 20), func(p Point, tile Tile){
    // Optional, all of the tiles that are in the view now
})

// Poll the inbox (in reality this would need to be with a select, and a goroutine)
for {
    update := <-view.Inbox
    // Do something with update.Point, update.Tile
}

The MoveBy() method allows you to move the view in a specific direction. It takes in a x,y vector but it can contain negative values. In the example below, we move the view upwards by 5 tiles. In addition, we can also provide an iterator and do something with all of the tiles that have entered the view (e.g. show them to the player).

view.MoveBy(0, 5, func(p Point, tile Tile){
    // Every tile which entered our view   
})

Similarly, MoveAt() method allows you to move the view at a specific location provided by the coordinates. The size of the view stays the same and the iterator will be called for all of the new tiles that have entered the view port.

view.MoveAt(At(10, 10), func(p Point, tile Tile){
    // Every tile which entered our view   
})

The Resize() method allows you to resize and update the view port. As usual, the iterator will be called for all of the new tiles that have entered the view port.

viewRect := NewRect(10, 10, 30, 30)
view.Resize(viewRect, func(p Point, tile Tile){
    // Every tile which entered our view   
})

The Close() method should be called when you are done with the view, since it unsubscribes all of the notifications. Be careful, if you do not close the view when you are done with it, it will lead to memory leaks since it will continue to observe the grid and receive notifications.

// Unsubscribe from notifications and close the view
view.Close()

Save & Load

The library also provides a way to save the Grid to an io.Writer and load it from an io.Reader by using WriteTo() method and ReadFrom() function. Keep in mind that the save/load mechanism does not do any compression, but in practice you should use to a compressor if you want your maps to not take too much of the disk space - snappy is a good option for this since it's fast and compresses relatively well.

The WriteTo() method of the grid only requires a specific io.Writer to be passed and returns a number of bytes that have been written down to it as well if any specific error has occured. Below is an example of how to save the grid into a compressed buffer.

// Prepare the output buffer and compressor
output := new(bytes.Buffer)
writer, err := flate.NewWriter(output, flate.BestSpeed)
if err != nil {
    // ...
}

defer writer.Close()            // Make sure we flush the compressor
_, err := grid.WriteTo(writer)  // Write the grid
if err != nil {
    // ...
}

The ReadFrom() function allows you to read the Grid from a particular reader. To complement the example above, the one below shows how to read a compressed grid using this function.

// Prepare a compressed reader over the buffer
reader := flate.NewReader(output)

// Read the Grid
grid, err := ReadFrom(reader)
if err != nil{
    // ...
}

Benchmarks

This library contains quite a bit of various micro-benchmarks to make sure that everything stays pretty fast. Feel free to clone and play around with them yourself. Below are the benchmarks which we have, most of them are running on relatively large grids.

enchmarkGrid/each-8                  514   2309290 ns/op         0 B/op   0 allocs/op
BenchmarkGrid/neighbors-8       14809420      81.0 ns/op         0 B/op   0 allocs/op
BenchmarkGrid/within-8             18488     64583 ns/op         0 B/op   0 allocs/op
BenchmarkGrid/at-8              59917014      19.4 ns/op         0 B/op   0 allocs/op
BenchmarkGrid/write-8           59944251      19.3 ns/op         0 B/op   0 allocs/op
BenchmarkGrid/merge-8           49933837      24.0 ns/op         0 B/op   0 allocs/op
BenchmarkPath/9x9-8               206911      5361 ns/op     16468 B/op   3 allocs/op
BenchmarkPath/300x300-8              460   2558757 ns/op   7801175 B/op   4 allocs/op
BenchmarkPath/381x381-8              454   2689466 ns/op  62394354 B/op   4 allocs/op
BenchmarkPath/384x384-8              152   7809399 ns/op  62396320 B/op   5 allocs/op
BenchmarkPath/6144x6144-8            141   7461047 ns/op  62395595 B/op   3 allocs/op
BenchmarkPath/6147x6147-8            160   7462501 ns/op  62395357 B/op   3 allocs/op
BenchmarkAround/3r-8              333166      3485 ns/op       385 B/op   1 allocs/op
BenchmarkAround/5r-8              153844      7833 ns/op       931 B/op   2 allocs/op
BenchmarkAround/10r-8              59702     20083 ns/op      3489 B/op   2 allocs/op
BenchmarkHeap-8                    97560     12229 ns/op      3968 B/op   5 allocs/op
BenchmarkPoint/within-8       1000000000     0.218 ns/op         0 B/op   0 allocs/op
BenchmarkPoint/within-rect-8  1000000000     0.218 ns/op         0 B/op   0 allocs/op
BenchmarkPoint/interleave-8   1000000000     0.652 ns/op         0 B/op   0 allocs/op
BenchmarkStore/save-8               7045    173594 ns/op         8 B/op   1 allocs/op
BenchmarkStore/read-8               2666    453553 ns/op    651594 B/op   8 allocs/op
BenchmarkView/write-8           10619553       111 ns/op        16 B/op   1 allocs/op
BenchmarkView/move-8                7500    160667 ns/op         0 B/op   0 allocs/op

Contributing

We are open to contributions, feel free to submit a pull request and we'll review it as quickly as we can. This library is maintained by Roman Atachiants

License

Tile is licensed under the [MIT License](LICENSE.md).


*Note that all licence references and agreements mentioned in the tile README section above are relevant to that project's source code only.