[cairo] [PATCH] V3: Use NEAREST filter when possible
Chris Wilson
chris at chris-wilson.co.uk
Tue Aug 12 11:59:53 PDT 2014
On Tue, Aug 12, 2014 at 11:47:58AM -0700, Bill Spitzak wrote:
> Further fix to use a #define for the epsilon value.
>
> Make _cairo_matrix_has_unity_scale return true for approximate 90 rotations
> to work around inaccuracy of sin/cos(M_PI_2).
>
> This fails after 14 additions of M_PI_2 to itself as a float argument to
> cairo_rotate, but the failure is in the detection of the integer translate,
> not in the trig components. I believe this is due to the matrix inversion,
> which may need similar rounding.
> ---
> src/cairo-matrix.c | 39 +++++++++++++++++++++++++--------------
> src/cairo-pattern.c | 2 +-
> src/cairo-xcb-surface-render.c | 7 ++-----
> 3 files changed, 28 insertions(+), 20 deletions(-)
>
> diff --git a/src/cairo-matrix.c b/src/cairo-matrix.c
> index ba975be..881e37d 100644
> --- a/src/cairo-matrix.c
> +++ b/src/cairo-matrix.c
> @@ -748,23 +748,34 @@ _cairo_matrix_is_integer_translation (const cairo_matrix_t *matrix,
> return FALSE;
> }
>
> +#define SCALING_EPSILON _cairo_fixed_to_double(1)
> +
> +/* This only returns true if the matrix is 90 degree rotations or
> + * flips. It appears calling code is relying on this. It will return
> + * false for other rotations even if the scale is one. Approximations
> + * are allowed to handle matricies filled in using trig functions
> + * such as sin(M_PI_2).
> + */
> cairo_bool_t
> _cairo_matrix_has_unity_scale (const cairo_matrix_t *matrix)
> {
> - if (matrix->xy == 0.0 && matrix->yx == 0.0) {
> - if (! (matrix->xx == 1.0 || matrix->xx == -1.0))
> - return FALSE;
> - if (! (matrix->yy == 1.0 || matrix->yy == -1.0))
> - return FALSE;
> - } else if (matrix->xx == 0.0 && matrix->yy == 0.0) {
> - if (! (matrix->xy == 1.0 || matrix->xy == -1.0))
> - return FALSE;
> - if (! (matrix->yx == 1.0 || matrix->yx == -1.0))
> - return FALSE;
> - } else
> - return FALSE;
> -
> - return TRUE;
> + /* check that the determinant is near +/-1 */
> + double dsquared = matrix->xx * matrix->yy - matrix->xy * matrix->yx;
> + printf("d is %g\n", dsquared);
> + dsquared *= dsquared;
> + if (fabs (dsquared - 1.0) < SCALING_EPSILON) {
double det = _cairo_matrix_compute_determinant(matrix);
if (fabs(det * det - 1.0) < SCALING_EPSILON) {
With that minor adjustment,
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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