Just give a resource_id to this layer, it will detect automatically the type of the resource and it will display it correctly. Supported resource types are : PNG / APNG / PDCI / PDCS
Create and destroy your layer with generic_bitmap_layer_create and generic_bitmap_layer_destroy like every pebble XXX_layer.
Set the resource of your layer with generic_bitmap_layer_set_resource(GenericBitmapLayer* gbl, uint32_t resource_id). You can change the resource dynamically, your layer will be updated.
This project contains a demo, just try it !