Core types

Godot has a rich set of classes and templates that compose its core, and everything is built upon them.

This reference will try to list them in order for their better understanding.

Definitions

Godot uses the standard C98 datatypes, such as uint8_t, uint32_t, int64_t, etc. which are nowadays supported by every compiler. Reinventing the wheel for those is not fun, as it makes code more difficult to read.

In general, care is not taken to use the most efficient datatype for a given task unless using large structures or arrays. int is used through most of the code unless necessary. This is done because nowadays every device has at least a 32 bits bus and can do such operations in one cycle. It makes code more readable too.

For files or memory sizes, size_t is used, which is warranted to be 64 bits.

For Unicode characters, CharType instead of wchar_t is used, because many architectures have 4 bytes long wchar_t, where 2 bytes might be desired. However, by default, this has not been forced and CharType maps directly to wchar_t.

References:

Memory model

PC is a wonderful architecture. Computers often have gigabytes of RAM, terabytes of storage and gigahertz of CPU, and when an application needs more resources the OS will just swap out the inactive ones. Other architectures (like mobile or consoles) are in general more limited.

The most common memory model is the heap, where an application will request a region of memory, and the underlying OS will try to fit it somewhere and return it. This often works best and is very flexible, but over time and with abuse, this can lead to segmentation.

Segmentation slowly creates holes that are too small for most common allocations, so that memory is wasted. There is a lot of literature about heap and segmentation, so this topic will not be developed further here. Modern operating systems use paged memory, which helps mitigate the problem of segmentation but doesn’t solve it.

However, in many studies and tests, it is shown that given enough memory, if the maximum allocation size is below a given threshold in proportion to the maximum heap size and proportion of memory intended to be unused, segmentation will not be a problem over time as it will remain constant. In other words, just leave 10-20% of your memory free and perform all small allocations and you are fine.

Godot ensures that all objects that can be allocated dynamically are small (less than a few kb at most). But what happens if an allocation is too large (like an image or mesh geometry or large array)? In this case Godot has the option to use a dynamic memory pool. This memory needs to be locked to be accessed, and if an allocation runs out of memory, the pool will be rearranged and compacted on demand. Depending on the need of the game, the programmer can configure the dynamic memory pool size.

Allocating memory

Godot has many tools for tracking memory usage in a game, especially during debug. Because of this, the regular C and C++ library calls should not be used. Instead, a few other ones are provided.

For C-style allocation, Godot provides a few macros:

memalloc()
memrealloc()
memfree()

These are equivalent to the usual malloc, realloc, free of the standard library.

For C++-style allocation, special macros are provided:

memnew( Class / Class(args) )
memdelete( instance )

memnew_arr( Class , amount )
memdelete_arr( pointer to array )

which are equivalent to new, delete, new[] and delete[].

memnew/memdelete also use a little C++ magic and notify Objects right after they are created, and right before they are deleted.

For dynamic memory, the DVector<> template is provided. Just use it like:

DVector<int>

DVector is just a standard vector class, it can be accessed using the [] operator, but that’s probably slow for large amount of accesses (as it has to lock internally). A few helpers exist for this:

DVector<int>::Read r = dvector.read()
int someint = r[4]

and

DVector<int>::Write w = dvector.write()
w[4]=22;

respectively. These allow fast read/write from DVectors and keep it locked until they go out of scope.

Containers

Godot provides also a set of common containers:

  • Vector
  • List
  • Set
  • Map

They are very simple and aim to be as minimal as possible, as templates in C++ are often inlined and make the binary size much fatter, both in debug symbols and code. List, Set and Map can be iterated using pointers, like this:

for(List<int>::Element *E=somelist.front();E;E=E->next()) {
    print_line(E->get()); //print the element
}

The Vector<> class also has a few nice features:

  • It does copy on write, so making copies of it is cheap as long as they are not modified.
  • It supports multi-threading, by using atomic operations on the reference counter.

String

Godot also provides a String class. This class has a huge amount of features, full Unicode support in all the functions (like case operations) and utf8 parsing/extracting, as well as helpers for conversion and visualization.

References:

StringName

StringNames are like a String, but they are unique. Creating a StringName from a string results in a unique internal pointer for all equal strings. StringNames are really useful for using strings as identifier, as comparing them is basically comparing a pointer.

Creation of a StringName (especially a new one) is slow, but comparison is fast.

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Math types

There are several linear math types available in the core/math directory, they are basically just that.

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NodePath

This is a special datatype used for storing paths in a scene tree and referencing them fast.

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RID

RIDs are resource IDs. Servers use these to reference data stored in them. RIDs are opaque, meaning that the data they reference can’t be accessed directly. RIDs are unique, even for different types of referenced data.

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