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#ActualBrother Bob

Posted 27 September 2012 - 01:30 PM

It is an extension, but it is an extension that has been promoted to the core API after it has been widely adopted and accepted. When it was promoted from extension to core function, it is entirely possible that functions change in the way they work, or that function names change (not counting dropping the ARB suffix), or that functions are removed entirely.

Lets say that there is an extension GL_ARB_foo which has a function named glFooARB. The extension is widely adopted and promoted to the core in version X of OpenGL. When promoted to the core, the extension suffix is dropped, and the function name becomes glFoo. At this point, a driver that doesn't provide support for OpenGL version X can choose to support GL_ARB_foo and must subsequently provide the function glFooARB. Once the driver implements OpenGL version X or later, it must now provide the function named glFoo since that is what's required for version X.

The driver can, if it chooses, provide an implementation for version X but not announce support for GL_ARB_foo. There is nothing wrong here, because GL_ARB_foo itself is not a part of the core API, but the function it provided was.

A driver is only required to provide functions for the version it claims to support and for the extensions listed in the extension string. If the extension string does not include GL_ARB_foo, then glFooARB is not provided. If version X is provided but GL_ARB_foo is not listed, then glFoo is available but not glFooARB, even though they may be the exact same functions.

If you look in the specification for ARB_geometry_shader4, you will see that all new functions has an ARB-suffix. This denotes that the function belongs to an ARB extension. If you look up the core API specification you will see that the corresponding functions does not have the ARB suffix. They are different functions as far as the specification goes.

#2Brother Bob

Posted 27 September 2012 - 01:29 PM

It is an extension, but it is an extension that has been promoted to the core API after it has been widely adopted and accepted. When it was promoted from extension to core function, it is entirely possible that functions change in the way they work, or that function names change (not counting dropping the ARB suffix), or that functions are removed entirely.

Lets say that there is an extension GL_ARB_foo which has a function named glFooARB. The extension is widely adopted and promoted to the core in version X of OpenGL. When promoted to the core, the extension suffix is dropped, and the function name becomes glFoo. At this point, a driver that doesn't provide support for OpenGL version X can choose to support GL_ARB_foo and must subsequently provide the function glFooARB. Once the driver implements OpenGL version X or later, it must now provide the function named glFoo since that is what's required for version X.

The driver can, if it chooses, provide an implementation for version X but not announce support for GL_ARB_foo. There is nothing wrong here, because GL_ARB_foo itself is not a part of the core API, but the function it provided was.

A driver is only required to provide functions for the version it claims to support and for the extensions listed in the extension string. If the extension string does not include GL_ARB_foo, then glFooARB is not provided.

If you look in the specification for ARB_geometry_shader4, you will see that all new functions has an ARB-suffix. This denotes that the function belongs to an ARB extension. If you look up the core API specification you will see that the corresponding functions does not have the ARB suffix. They are different functions as far as the specification goes.

#1Brother Bob

Posted 27 September 2012 - 01:28 PM

It is an extension, but it is an extension that has been promoted to the core API after it has been widely adopted and accepted. When it was promoted from extension to core function, it is entirely possible that functions change in the way they work, or that function names change (not counting dropping the ARB suffix), or that functions are removed entirely.

Lets say that there is an extension GL_ARB_foo which has a function named glFooARB. The extension is widely adopted and promoted to the core in version X of OpenGL. When promoted to the core, the extension suffix is dropped, and the function name becomes glFoo. At this point, a driver that doesn't provide support for OpenGL version X can choose to support GL_ARB_foo and must subsequently provide the function glFooARB. Once the driver implements OpenGL version X or later, it must now provide the function named glFoo since that is what's required for version X.

the driver can, it it chooses, provide an implementation for version X but not announce support for GL_ARB_foo. There is nothing wrong here, because GL_ARB_foo itself is not a part of the core API, but the function it provided was.

A driver is only required to provide functions for the version it claims to support and for the extensions listed in the extension string. If the extension string does not include GL_ARB_foo, then glFooARB is not provided.

If you look in the specification for ARB_geometry_shader4, you will see that all new functions has an ARB-suffix. This denotes that the function belongs to an ARB extension. If you look up the core API specification you will see that the corresponding functions does not have the ARB suffix. They are different functions as far as the specification goes.

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