On Mon, Jan 4, 2016 at 5:12 AM, <spit...@gmail.com> wrote: > From: Bill Spitzak <spit...@gmail.com> > > Simpsons uses cubic curve fitting, with 3 samples defining each cubic. This > makes the weights of the samples be in a pattern of 1,4,2,4,2...4,1, and then > dividing the result by 3. > > The previous code was using weights of 1,2,6,6...6,2,1. Since it divided by > 3 this produced about 2x the desired value (the normalization fixed this). > Also this is effectively a linear interpolation, not Simpsons integration. > > With this fix the integration is accurate enough that the number of samples > could be reduced a lot. Likely even 16 samples is too many.
You forgot to sign-off > --- > pixman/pixman-filter.c | 17 +++++++++++------ > 1 file changed, 11 insertions(+), 6 deletions(-) > > diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c > index 15f9069..5677431 100644 > --- a/pixman/pixman-filter.c > +++ b/pixman/pixman-filter.c > @@ -189,8 +189,10 @@ integral (pixman_kernel_t reconstruct, double x1, > } > else > { > - /* Integration via Simpson's rule */ > -#define N_SEGMENTS 128 > + /* Integration via Simpson's rule > + * See http://www.intmath.com/integration/6-simpsons-rule.php > + */ > +#define N_SEGMENTS 16 > #define SAMPLE(a1, a2) \ > (filters[reconstruct].func ((a1)) * filters[sample].func ((a2) / > scale)) > > @@ -204,11 +206,14 @@ integral (pixman_kernel_t reconstruct, double x1, > { > double a1 = x1 + h * i; > double a2 = x2 + h * i; > + s += 4 * SAMPLE(a1, a2); > + } > > - s += 2 * SAMPLE (a1, a2); > - > - if (i >= 2 && i < N_SEGMENTS - 1) > - s += 4 * SAMPLE (a1, a2); > + for (i = 2; i < N_SEGMENTS; i += 2) > + { > + double a1 = x1 + h * i; > + double a2 = x2 + h * i; > + s += 2 * SAMPLE(a1, a2); > } > > s += SAMPLE (x1 + width, x2 + width); > -- > 1.9.1 > > _______________________________________________ > Pixman mailing list > Pixman@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/pixman Patch is: Reviewed-by: Oded Gabbay <oded.gab...@gmail.com> _______________________________________________ Pixman mailing list Pixman@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/pixman