On Mon, Jun 2, 2014 at 4:59 AM, Robert O'Callahan <rob...@ocallahan.org> wrote:
> On Mon, Jun 2, 2014 at 3:19 PM, Rik Cabanier <caban...@gmail.com> wrote: > >> isIdentity() indeed suffers from rounding errors but since it's useful, >> I'm >> hesitant to remove it. >> In our rendering libraries at Adobe, we check if a matrix is *almost* >> identity. Maybe we can do the same here? >> > > One option would be to make "isIdentity" and "is2D" state bits in the > object rather than predicates on the matrix coefficients. Then for each > matrix operation, we would define how it affects the isIdentity and is2D > bits. For example we could say translate(tx, ty, tz)'s result isIdentity if > and only if the source matrix isIdentity and tx, ty and tz are all exactly > 0.0, and the result is2D if and only if the source matrix is2D and tz is > exactly 0.0. > > With that approach, isIdentity and is2D would be much less sensitive to > precision issues. In particular they'd be independent of the precision used > to compute and store store matrix elements, which would be helpful I think. > That would work for me. The constructors would still need to test to make sure that the matrix is 2D and Identity but that wouldn't suffer from the rounding issues that Benoit brought up. _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
