[Mesa-dev] [PATCH 00/23] Don't pollute the buffer object namespace in meta

[Ian Romanick]

Also on the meta-cannot-use-Gen branch of my fd.o Mesa tree.  This
branch will contain all of the current work... including patches beyond
this series.

On 11/09/2015 04:55 PM, Ian Romanick wrote:
> In OpenGL ES (all versions!) and OpenGL compatibility profile,
> applications don't have to call Gen functions.  The GL spec is very
> clear about how you can mix-and-match generated names and non-generated
> names: you can use any name you want for a particular object type until
> you call the Gen function for that object type.  After calling Gen,
> making up your own names is not guaranteed to work.
> 
> Meta uses Gen all over the place, and this can conflict with names the
> application may try to use.  It's not hard to find OpenGL demos that do
> things like:
> 
>    glBindTexture(GL_TEXTURE_2D, 1);
>    ...    
> 
>    glBindTexture(GL_TEXTURE_2D, 2);
>    ...    
> 
> I suspect there are even demos in the mesa-demos repository that do
> this.
> 
> This is, IMO, a case of premature optimization in OpenGL 1.0.  In OpenGL
> 1.0, almost all implementations were indirect-renderers.  If names had
> to be allocated from the server, that meant you had to (queue dramatic
> music) have an extra round-trip to the server to get some names.  In
> addition, allowing user-defined names meant that you could name the
> display list (the only pseudo-object in OpenGL 1.0) that drew the letter
> A, (int)'A'.  It was common to see text rendering loops like:
> 
>     while (*str) {
>         glCallList((GLuint)*str);
>         str++;
>     }
> 
> On the systems of 1992, that may have mattered.  It's certainly not an
> optimization that has mattered on any system that I've programmed OpenGL
> on, and the damage that it does inside drivers is... this is a 23-patch
> series to fix a bug that should never have existed!
> 
> Here's the problem scenario:
>     
>  - Application calls a meta function that generates a name.  The first
>    Gen will return 1.
> 
>  - Application decides to use the same name for an object of the same
>    type without calling Gen.  Many demo programs use names 1, 2, 3,
>    etc. without calling Gen.
> 
>  - Application calls the meta function again, and the meta function
>    replaces the data.  The application's data is lost, and the app
>    fails.  Have fun debugging that.
> 
> This patch series is longer than is strictly necessary.  I wanted to
> make each individual step easy to review.  It's a good thing too.  There
> were a couple places where I made typos or cut-and-paste errors that
> were much easier to bisect.
> 
> This patch series also *only* fixes the problem for buffer objects.
> Texture, sampler, framebuffer, renderbuffer, and assembly program
> objects still need to be fixed.
> 
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