[Mesa-dev] [PATCH 1/2] st/mesa: allow creating buffers of size = 0

[Brian Paul]

OK, handling this in the st_draw.c code is trivial.  That'll take care 
of the piglit test.  I'll have to follow-up later with other state 
tracker changes for other cases.

-Brian

On 11/14/2011 08:13 AM, Jose Fonseca wrote:
> Is it really necessary to bother pipe drivers with zero size buffers?
>
> It looks like a useless corner case, which will cause all sort of implementations problems (e.g., malloc(0) may return NULL; kernel drivers will likely refuse 0 size buffers), so pipe drivers will need a lot of
>
>    if (buffer->size == 0) {
>      // don't do something stupid
>    } else {
>      // business as usual
>    }
>
> I'd prefer see this be completely handled in the state tracker.
>
> Jose
>
>
> ----- Original Message -----
>> Calling glBufferData(size=0) is legal.  Instead of no-oping it, go
>> ahead
>> and create a gallium buffer of size zero.  This lets us avoid a bunch
>> of
>> NULL pointer checking elsewhere.  In the case of a zero-sized VBO,
>> the
>> bounds checking we do later will prevent invalid memory accesses.
>> ---
>>   src/mesa/state_tracker/st_cb_bufferobjects.c |   22
>>   +++++++++-------------
>>   1 files changed, 9 insertions(+), 13 deletions(-)
>>
>> diff --git a/src/mesa/state_tracker/st_cb_bufferobjects.c
>> b/src/mesa/state_tracker/st_cb_bufferobjects.c
>> index adac92f..3abf029 100644
>> --- a/src/mesa/state_tracker/st_cb_bufferobjects.c
>> +++ b/src/mesa/state_tracker/st_cb_bufferobjects.c
>> @@ -221,21 +221,17 @@ st_bufferobj_data(struct gl_context *ctx,
>>
>>      pipe_resource_reference(&st_obj->buffer, NULL );
>>
>> -   if (size != 0) {
>> -      st_obj->buffer = pipe_buffer_create(pipe->screen, bind,
>> -                                          pipe_usage, size);
>> -
>> -      if (!st_obj->buffer) {
>> -         /* out of memory */
>> -         st_obj->Base.Size = 0;
>> -         return GL_FALSE;
>> -      }
>> -
>> -      if (data)
>> -         pipe_buffer_write(pipe, st_obj->buffer, 0, size, data);
>> -      return GL_TRUE;
>> +   st_obj->buffer = pipe_buffer_create(pipe->screen, bind,
>> pipe_usage, size);
>> +
>> +   if (!st_obj->buffer) {
>> +      /* out of memory */
>> +      st_obj->Base.Size = 0;
>> +      return GL_FALSE;
>>      }
>>
>> +   if (data&&  size>  0)
>> +      pipe_buffer_write(pipe, st_obj->buffer, 0, size, data);
>> +
>>      return GL_TRUE;
>>   }
>>
>> --
>> 1.7.3.4
>>
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