Am Montag, den 09.07.2018, 09:54 +0200 schrieb Erik Faye-Lund: > On 06. juli 2018 18:43, Roland Scheidegger wrote: > > > > Personally I think it's _much_ better to lie about the supported GL > > version rather than the maximum vertex attrib stride (I don't know > > if dEQP would actually have a test which tests for the max stride > > also working than just being advertized, which would be way more > > relevant and fail in any case). > > I don't think I agree in this case; OpenGL 4.4 applications that use > *exactly* strides of 2048probably won't even check the max-stride, as > it's guaranteed to work by the standard anyway. Applications that use > *more* might check for this value, but as the query was introduced in > 4.4 it's likely that applications will just get a gl-error down an > unexpected code-path, which can lead to the wrong attribute bound > (possibly pointing to client-memory, which can lead to segfaults). > Lying about the max attribute stride will "just" lead to rendering > glitches.
FWIW: The value probably comes from the definition of SQ_VTX_CONSTANT_WORD2_0 where a stride is defined as a value of 11 bits that is 0-2047, and when the value is send to the graphics card it will be masked to use only these 11 bits, which means when an applciation uses a stride of 2048 then the value zero will be uploaded. Also I seem to remember that the blob advertised OpenGL 4.4 - now whether they lied about it, had some special code path, or a value of zero is actually interpreted as 2048 (which would actually make sense to me), I don't know. - Well, when I get around to it, I'll write a piglit that sees what happens in that case ... best, Gert _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
