Custom resource format loaders


ResourceFormatLoader is a factory interface for loading file assets. Resources are primary containers. When load is called on the same file path again, the previous loaded Resource will be referenced. Naturally, loaded resources must be stateless.

This guide assumes the reader knows how to create C++ modules and Godot data types. If not, refer to this guide: Custom modules in C++


What for?

  • Adding new support for many file formats

  • Audio formats

  • Video formats

  • Machine learning models

What not?

  • Raster images

ImageFormatLoader should be used to load images.


Creating a ResourceFormatLoader

Each file format consist of a data container and a ResourceFormatLoader.

ResourceFormatLoaders are classes which return all the necessary metadata for supporting new extensions in Godot. The class must return the format name and the extension string.

In addition, ResourceFormatLoaders must convert file paths into resources with the load function. To load a resource, load must read and handle data serialization.

/* resource_loader_json.h */


#include "core/io/resource_loader.h"

class ResourceFormatLoaderJson : public ResourceFormatLoader {
    GDCLASS(ResourceFormatLoaderJson, ResourceFormatLoader);
    virtual RES load(const String &p_path, const String &p_original_path, Error *r_error = NULL);
    virtual void get_recognized_extensions(List<String> *r_extensions) const;
    virtual bool handles_type(const String &p_type) const;
    virtual String get_resource_type(const String &p_path) const;
/* resource_loader_json.cpp */

#include "resource_loader_json.h"

#include "resource_json.h"

RES ResourceFormatLoaderJson::load(const String &p_path, const String &p_original_path, Error *r_error) {
Ref<JsonResource> json = memnew(JsonResource);
    if (r_error) {
            *r_error = OK;
    Error err = json->load_file(p_path);
    return json;

void ResourceFormatLoaderJson::get_recognized_extensions(List<String> *r_extensions) const {
    if (!r_extensions->find("json")) {

String ResourceFormatLoaderJson::get_resource_type(const String &p_path) const {
    return "Resource";

bool ResourceFormatLoaderJson::handles_type(const String &p_type) const {
    return ClassDB::is_parent_class(p_type, "Resource");

Creating a ResourceFormatSaver

If you'd like to be able to edit and save a resource, you can implement a ResourceFormatSaver:

/* resource_saver_json.h */


#include "core/io/resource_saver.h"

class ResourceFormatSaverJson : public ResourceFormatSaver {
    GDCLASS(ResourceFormatSaverJson, ResourceFormatSaver);
    virtual Error save(const String &p_path, const RES &p_resource, uint32_t p_flags = 0);
    virtual bool recognize(const RES &p_resource) const;
    virtual void get_recognized_extensions(const RES &p_resource, List<String> *r_extensions) const;
/* resource_saver_json.cpp */

#include "resource_saver_json.h"

#include "resource_json.h"
#include "scene/resources/resource_format_text.h"