On 09/03/16 20:15, Kyle Brenneman wrote:
The current implementation of libglvnd uses a new X extension called x11glvnd to look up a vendor name for each screen and to find a screen number for a GLXDrawable.But, Adam Jackson pointed out that a GLX extension could do the same job more cleanly: Looking up a vendor name is just querying a per-screen string, which GLXQueryServerString does. Looking up a screen number for a drawable could work by adding a GLX_SCREEN attribute to the GLXGetDrawableAttributes reply. Based on that idea, I've written up a rough draft of a GLX extension spec. Any comments, questions, or suggestions are welcome, of course. -Kyle Name EXT_libglvnd Name Strings GLX_EXT_libglvnd Contact Kyle Brenneman, NVIDIA, kbrenneman at nvidia.com Contributors Kyle Brenneman Adam Jackson Status XXX - Not complete yet Version Last Modified Date: March 8, 2016 Revision: 1 Number ??? Dependencies GLX version 1.3 is required. This specification is written against the wording of the GLX 1.4 Specification. Overview This extension allows the vendor-neutral GLX client library, libglvnd, to determine which vendor-specific driver is needed to support a given GLX drawable or X11 screen. This GLX extension is not intended to be used directly by applications. Instead, it is intended to be used by the GLX client library. IP Status No known IP claims. New Procedures and Functions None New Types None New Tokens Accepted by the <name> parameter of glXQueryServerString: GLX_VENDOR_NAMES_EXT 0x???? Additions to Chapter 3 of the GLX 1.4 Specification (Functions and Errors) [Modify Section 3.3.2, GLX Versioning] [Replace the 2nd sentence of the 5th paragraph with the following] "The possible values for <name> and the format of the strings is the same as for glXGetClientString. <name> may also be GLX_VENDOR_NAMES_EXT." [Add the following paragraph to the end of the section] "If <name> is GLX_VENDOR_NAMES_EXT, then the returned string is a space-separated sequence of vendor names. The names are in order of preference, with the most preferred vendor first." [Modify Section 3.3.6, Querying Attributes] [Replace the 2nd sentence of the 1st paragraph with the following] "<attribute> must be set to one of GLX_WIDTH, GLX_HEIGHT, GLX_PRESERVED_CONTENTS, GLX_LARGEST_PBUFFER, GLX_FBCONFIG_ID, or GLX_SCREEN" [Add the following paragraph just before the last of the section] "If <attribute> is GLX_SCREEN, then <value> will be the screen number that the drawable was created on." GLX Protocol This extension does not add any new requests. The GLX_VENDOR_NAMES_EXT enum is used with the existing glXQueryServerString request, and GLX_SCREEN is added to the attributes in the glXGetDrawableAttributes reply. Errors None Issues 1) Should GLX_VENDOR_NAMES_EXT contain a single vendor name or a list of names? Allowing multiple names would allow for multiple client-side drivers that work with a single server-side driver. With only a single name, selecting between multiple client drivers would require some form of additional configuration. 2) How are vendor names defined and interpreted? The vendor names for a screen are defined based on the server's GLX implementation. Typically, a server will simply send the name of the driver that controls the screen. The GLX client library is responsible for translating the vendor name to a vendor library name. The details of the translation are part of the interface between the vendor library and the GLX client library, and so is not defined in this specification. 3) What order should the vendor names be returned in? The GLX client library will try to load and use each vendor name, in the order that the server lists them. It will stop when it finds the first vendor that works.
That could be a hacky way of handling the case where multiple 3D drivers could be used to drive the same GPU. This may be necessary in the future if two mesa drivers support the same GPU but one is considered better than the other. We can also imagine a case where a proprietary driver would need to be co-installable with an open source one and would still use the same DDX. Isn't that what AMD is going to do soon? Did anyone think about this case?
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