[Mesa-dev] [PATCH 1/3] mesa: fix glPushAttrib(0) / glPopAttrib() error

[Jose Fonseca]

On 25/05/15 15:41, Brian Paul wrote:
> If the glPushAttrib() mask value was zero we didn't actually push
> anything onto the attribute stack.  A subsequent glPopAttrib() call
> would generate a GL_STACK_UNDERFLOW error.  Now push a dummy attribute
> in that case to prevent the error.
>
> Mesa now matches nvidia's behavior.
> ---
>   src/mesa/main/attrib.c | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
>
> diff --git a/src/mesa/main/attrib.c b/src/mesa/main/attrib.c
> index b163c0a..365a79d 100644
> --- a/src/mesa/main/attrib.c
> +++ b/src/mesa/main/attrib.c
> @@ -177,6 +177,10 @@ struct texture_state
>   };
>
>
> +/** An unused GL_*_BIT value */
> +#define DUMMY_BIT 0x10000000



> +
> +
>   /**
>    * Allocate new attribute node of given type/kind.  Attach payload data.
>    * Insert it into the linked list named by 'head'.
> @@ -253,6 +257,15 @@ _mesa_PushAttrib(GLbitfield mask)
>      /* groups specified by the mask. */
>      head = NULL;
>
> +   if (mask == 0) {
> +      /* if mask is zero we still need to push something so that we
> +       * don't get a GL_STACK_UNDERFLOW error in glPopAttrib().
> +       */
> +      GLuint dummy = 0;
> +      if (!push_attrib(ctx, &head, DUMMY_BIT, sizeof(dummy), &dummy))
> +         goto end;
> +   }
> +
>      if (mask & GL_ACCUM_BUFFER_BIT) {
>         if (!push_attrib(ctx, &head, GL_ACCUM_BUFFER_BIT,
>                          sizeof(struct gl_accum_attrib),
> @@ -928,6 +941,10 @@ _mesa_PopAttrib(void)
>         }
>
>         switch (attr->kind) {
> +         case DUMMY_BIT:
> +            /* do nothing */
> +            break;
> +
>            case GL_ACCUM_BUFFER_BIT:
>               {
>                  const struct gl_accum_attrib *accum;
>

If I'm not mistaken, you could use 0 for DUMMY_BIT (instead of 
0x10000000), and therefore completely avoid the possibility of a clash.

Either way

Reviewed-by: Jose Fonseca <jfonseca at vmware.com>

Jose