Separation of Starboard from Cobalt


In creating Cobalt Evergreen, we needed to have as few differences in the code as we could from one platform to another. Simply put, that means we want to get rid of as many platform specific compile time macros as possible. Because of the large amount of platform differences we had previously, there were macros defined in a variety places, all of which require different cases to convert. The below sections go into the differences regarding changes to these macros from Cobalt 20 to 21 and from Starboard 11 to 12.

Optional APIs

In previous versions, there were a few APIs that could optionally defined and would only be enabled if certain macros were set. The platform would only have to implement the API if it set the macros accordingly. Now, those differences have been removed, and all platforms are required to implement these APIs. For convenience, we have provided stub functions for all implementations, which a platform can use without differences in Cobalt if they did not enable the API beforehand.

Migration from Configuration Macros to External Constants

Starboard configurations have moved from configuration.h and platform specific configuration_public.h files to files. They have also been changes from macros to extern consts. This means that Cobalt will be able to evaluate these variables at runtime instead of compile time. The declarations for all of these variables are located in configuration_constants.h, but each platform must define each variable individually, i.e. as

#include "starboard/configuration_constants.h"

const int32_t kSbFileMaxName = 64;

There are two changes that are a result of this migration:

  1. There is no longer any form of inheritance. This means that if there are any configuration differences between two platforms, they must have separate files.
  2. There are no longer default values for any variable. Because we cannot inherit values, we would not be able to receive a default value for any one, so each platform must have a definition for every configuration variable.

Migration from GYP Variables to Cobalt Extensions

Cobalt configurations have moved from cobalt_configuration.gypi and platform specific gyp_configuration.gypi files to Cobalt extensions, primarily CobaltExtensionConfigurationApi, but including the CobaltExtensionGraphicsApi.

Some variables were already in the process of being deprecated, sometimes with a replacement. In those cases, that path was followed.

Implementing the Cobalt extension is completely optional, and when calling the functions corresponding to the old GYP variable, there will be a default value that the function will be able to fall back onto if the extension has not been implemented. That being said, if there is a single function the platform needs a custom implementation for, it must completely implement the CobaltExtensionConfigurationApi. For convenience, we have provided default functions to use to define the API if desired.


For migrating from macros, partners will have to treat their use differently! I.e. string literal vs const char* in their implementations. Add an overview of all of the cases of this migration in runtime code.