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.romant...@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 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev