[Mesa-dev] [PATCH v3] mesa: rotation of 0-vector

[Sergii Romantsov]

Hello,
i've updated a test for the latest version of mesa-patch:
https://patchwork.freedesktop.org/patch/255629/
The image should looks for any driver (Windows, Nvidia, mesa) like this:
[image: Screenshot from 2018-10-10 13-47-56.png]

On Fri, Sep 21, 2018 at 4:21 PM Sergii Romantsov <sergii.romantsov at gmail.com>
wrote:

> Specification doesn't define behaviour for rotation of 0-vector.
> In https://github.com/KhronosGroup/OpenGL-API/issues/41 said that
> behaviour is undefined and agreed that it would be fine for
> implementation to do something useful for this.
> Windows and Nvidia drivers have a workaround for that.
> For compatibility proposed optimized version of computations.
> Specification defines a formula of rotation (see "OpenGL 4.6
> (Compatibility Profile) - May 14, 2018", paragraph "12.1.1 Matrices").
>
> Optimized formula will look so:
>
>                R = cos(angle) * I
>
> That is equavalent to logic that magnitude of (0,0,0)-vector is 1.0.
>
> -v2: logic moved to _math_matrix_rotate
>
> -v3: general optimization of computations
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100960
> Signed-off-by: Sergii Romantsov <sergii.romantsov at globallogic.com>
> ---
>  src/mesa/math/m_matrix.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/src/mesa/math/m_matrix.c b/src/mesa/math/m_matrix.c
> index 57a4953..3eef122 100644
> --- a/src/mesa/math/m_matrix.c
> +++ b/src/mesa/math/m_matrix.c
> @@ -824,6 +824,18 @@ _math_matrix_rotate( GLmatrix *mat,
>                 M(1,0) = s;
>              }
>           }
> +         else {
> +            /* https://bugs.freedesktop.org/show_bug.cgi?id=100960
> +             * https://github.com/KhronosGroup/OpenGL-API/issues/41
> +             * Here we will treat magnitude as 1.0 if it really 0.0.
> +             * So that is kind of workaround for empty-vectors to have
> +             * compatibility with Windows and Nvidia drivers.
> +             */
> +            optimized = GL_TRUE;
> +            M(0,0) = c;
> +            M(1,1) = c;
> +            M(2,2) = c;
> +         }
>        }
>        else if (z == 0.0F) {
>           optimized = GL_TRUE;
> --
> 2.7.4
>
>
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