[Mesa-dev] Potential spec change request for EXT_buffer_storage

[Ian Romanick]

On 11/04/2015 03:26 PM, Ryan Houdek wrote:
> I'm hoping to potentially convince about lowering the minimum
> requirement of EXT_buffer_storage from ES 3.1 to ES 3.0.
> The only thing that causes it to require ES 3.1 is glMemoryBarrier,
> which shouldn't really be a hard requirement since the extension can be
> used without it.
> This is also a similar situation with ARB_buffer_storage which Mesa
> currently exposes to all GL versions even though it should require GL 4.2.
> I have my attempt at a change to the spec as follows. I've never tried
> changing a spec page before so it's a bit new to me.

I think all of the drivers that support ARB_buffer_storage also support
ARB_texture_barrier.  At the very least I think you'd need to require
GL_MAP_CHOERENT_BIT with GL_MAP_PERSISTENT_BIT.

Also... Mesa is really close to getting OpenGL ES 3.1.  Are there any
drivers with which you want to use this extension that won't have GLES 3.1?

> diff --git a/EXT_buffer_storage.txt b/EXT_buffer_storage.txt
> index 03fcd6e..ea16fae 100644
> --- a/EXT_buffer_storage.txt
> +++ b/EXT_buffer_storage.txt
> @@ -30,8 +30,8 @@ Status
>  
>  Version
>  
> -    Last Modified Date:   May 1, 2015
> -    Author Revision:      3
> +    Last Modified Date:   November 4, 2015
> +    Author Revision:      4
>  
>  Number
>  
> @@ -39,10 +39,12 @@ Number
>  
>  Dependencies
>  
> -    OpenGL ES 3.1 is required.
> -
>      This extension is written against the OpenGL ES 3.1 (June 4, 2014)
> -    Specification.
> +    Specification, but can apply to prior specifications
> +
> +    Requires OpenGL ES 3.0

I think I'd just change the above to replace the current "required" line
with

   OpenGL ES 3.0 is required.

and leave the rest alone.

I think the rest of the edits look good.

> +
> +    This extension interacts with OpenGL ES 3.1.
>  
>      The definition of this extension is affected by the presence of
>      GL_EXT_direct_state_access.
> @@ -350,6 +352,50 @@ Additions to Chapter 7 of the OpenGL ES 3.1
> Specification,
>            by shaders prior to the barrier. Note that this may cause
> additional
>            synchronization operations.
>  
> +Dependencies on OpenGL ES 3.1
> +
> +    If OpenGL ES 3.1 is not supported apply the following modifications
> to the
> +    OpenGL ES 3.0.4 specification:
> +
> +    Append to the first paragraph of Section 2.10, "Buffer Objects", p. 32:
> +
> +    Under certain circumstances, the data store of a buffer object may
> +    be shared between the client and server and accessed simultaneously
> +    by both.
> +
> +    Modify Section 2.10.1 (Creating and Binding Buffer Objects)
> +
> +    Append to Table 2.7, "Buffer object parameters and their values", p.34:
> +
> +      
>  +------------------------------+---------+---------+------------------+
> +        |                              |         | Initial | Legal    
>        |
> +        | Name                         | Type    | Value   | Values    
>       |
> +      
>  +------------------------------+---------+---------+------------------+
> +        | BUFFER_IMMUTABLE_STORAGE_EXT | boolean | FALSE   | TRUE,
> FALSE      |
> +        | BUFFER_STORAGE_FLAGS_EXT     | int     | 0       | See
> section 6.2  |
> +      
>  +------------------------------+---------+---------+------------------+
> +
> +    Edits to section 6.2 "Creating and Modifying Buffer Object Data
> Stores" in
> +    ES 3.1 become edits to section 2.10.2 "Creating Buffer Object Data
> Stores"
> +    in ES 3.0.4.
> +
> +    Edits to section 6.3, "Mapping and Unmapping Buffer Data" in ES 3.1
> become
> +    edits in section 2.10.3 "Mapping and Unmapping Buffer Data" in ES 3.0.4
> +
> +    Edits to p.56, FlushMappedBufferRange, in ES 3.1 become edits in p.40
> +    in ES 3.0.4
> +
> +    Edits to section 6.3.2, "Effects of Mapping Buffers on Other GL
> Commands"
> +    in ES 3.1 become edits in p.41 in ES 3.0.4
> +
> +    Edits in section 6.7, "Buffer Object State" in ES 3.1 become edits in
> +    section 2.10.8 "Buffer Object State" in ES 3.0.4
> +
> +    Edits in section 20.4, "Buffer Object State", p.355 become edits in
> +    section 6.4, "Buffer Object State", p.247 in ES 3.0.4
> +
> +    If OpenGL ES 3.1 is not supported, ignore all references to
> MemoryBarrier
> +
>  New State
>  
>      Append to Table 20.4, "Buffer Object State", p.355:
> @@ -521,3 +567,5 @@ Revision History
>                                to make CPU writes visible to the GPU in
>                                this case without an explicit flush (Bug
>                                13578, sync w/ ARB_buffer_storage v.25).
> +
> +    4    04/11/15  rhoudek    Lower minimum dependency to ES 3.0
>