[Mesa-dev] [PATCH v3] mesa: rotation of 0-vector
Sergii Romantsov
sergii.romantsov at gmail.com
Fri Sep 21 13:21:11 UTC 2018
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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