[Mesa-dev] [PATCH] mesa: loosen small matrix determinant check

[Pekka Paalanen]

On Tue, 24 Jul 2012 11:31:59 -0600
Brian Paul <brianp at vmware.com> wrote:

> When computing a matrix inverse, if the determinant is too small we could hit
> a divide by zero.  There's a check to prevent this (we basically give up on
> computing the inverse and return the identity matrix.)  This patches loosens
> this test to fix a lighting bug reported by Lars Henning Wendt.
> 
> NOTE: This is a candidate for the 8.0 branch.
> ---
>  src/mesa/math/m_matrix.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/src/mesa/math/m_matrix.c b/src/mesa/math/m_matrix.c
> index 02aedba..ef377ee 100644
> --- a/src/mesa/math/m_matrix.c
> +++ b/src/mesa/math/m_matrix.c
> @@ -513,7 +513,7 @@ static GLboolean invert_matrix_3d_general( GLmatrix *mat )
>  
>     det = pos + neg;
>  
> -   if (det*det < 1e-25)
> +   if (det < 1e-25)
>        return GL_FALSE;
>  
>     det = 1.0F / det;

Hi,

just a fly-by question; doesn't that break if determinant is negative?
I.e. reflection transformations.


Thanks,
pq