Since the number of functions for a component type is large, we instead require the component extension to register only a Create/Destroy function.
DM_DECLARE_COMPONENT_TYPE(ComponentTypeSimpleDataExt, "simpledatac", dmSimpleData::CompTypeSimpleDataCreate, dmSimpleData::CompTypeSimpleDataDestroy);
Note here that the matching file type needs to be specified here!
It's not strictly necessary to create a context. However, for some global settings, e.g from reading from the settings file, the context is a good place to store this info.
MyComponentContext* context = new MyComponentContext;
context->m_MaxComponentsPerWorld = dmConfigFile::GetInt(ctx->m_Config, "mycomponent.max_count", 1024);
For each created collection in the game, the registered component types get a call to the "NewWorld" function (CompSimpleDataNewWorld in this example).
You create your own instance, and will store information relevant to that particular component type, such as the instances.
In this example we create an dmObjectPool to store our component instances in.
It allows us to have an array of a known max size, while at the same time allocate/deallocate objects at random, without the need to compact the array etc.
This is also a custom type which is allocated during the component "Create" function (here CompSimpleDataCreate).
You may choose to return a pointer, but since we are using an object pool, these instances are actually an uint32_t, which makes it easier to manage the object pool.
This however also means that we have to implement the CompSimpleDataGetComponent() which is responsible for translating our internal representation (our uint32_t) into an actual component pointer. It is mainly used in helper functions when implementing a Lua scripting api (example).
There are many functions available to implement, depending on what the desired feature set will be.
For a full example, it might be good to look at the comp_sprite.cpp or its likes.
In this example, we only required to implement a get function.
We get a call to the CompSimpleDataGetProperty function, with a request for the value of params.m_PropertyId. It is of type dmhash_t. Use e.g. dmHashString64()/dmHashBuffer64() to produce such hashes.
Note that the params.m_Options (type dmGameObject::PropertyOptions) allows the requester to ask for an index or a key.
If we get a valid request, then we fill out the out_value.m_Variant with a value, of type dmGameObject::PropertyVar, then we return dmGameObject::PROPERTY_RESULT_OK.