[PATCH weston] Simply the matrix calculation for zooming

[Jason Ekstrand]

On Apr 25, 2014 8:11 AM, "Pekka Paalanen" <ppaalanen at gmail.com> wrote:
>
> On Fri, 25 Apr 2014 13:19:37 +0100
> Neil Roberts <neil at linux.intel.com> wrote:
>
> > In order to apply the zoom transformation to the output matrix, Weston
was
> > doing the following:
> >
> > * Create a temporary matrix to hold the translation
> > * Invert the translation matrix using weston_matrix_invert into
> >   another temporary matrix
> > * Scale that matrix by the scale factor
> > * Multiply the current matrix with the temporary matrix
> >
> > Using weston_matrix_invert to invert a translation matrix is over the
top.
> > Instead we can just negate the values we pass to
weston_matrix_translate.
> > Matrix multiplication is associative so creating a temporary matrix to
hold the
> > scale and translation transform should be equivalent to just applying
them
> > directly to the output matrix.
> > ---
> >  src/compositor.c | 13 ++++---------
> >  1 file changed, 4 insertions(+), 9 deletions(-)
> >
> > diff --git a/src/compositor.c b/src/compositor.c
> > index fd2decb..f836cf7 100644
> > --- a/src/compositor.c
> > +++ b/src/compositor.c
> > @@ -3186,8 +3186,6 @@ WL_EXPORT void
> >  weston_output_update_matrix(struct weston_output *output)
> >  {
> >       float magnification;
> > -     struct weston_matrix camera;
> > -     struct weston_matrix modelview;
> >
> >       weston_matrix_init(&output->matrix);
> >       weston_matrix_translate(&output->matrix,
> > @@ -3202,14 +3200,11 @@ weston_output_update_matrix(struct
weston_output *output)
> >
> >       if (output->zoom.active) {
> >               magnification = 1 / (1 - output->zoom.spring_z.current);
> > -             weston_matrix_init(&camera);
> > -             weston_matrix_init(&modelview);
> >               weston_output_update_zoom(output);
> > -             weston_matrix_translate(&camera, output->zoom.trans_x,
> > -                                     -output->zoom.trans_y, 0);
> > -             weston_matrix_invert(&modelview, &camera);
> > -             weston_matrix_scale(&modelview, magnification,
magnification, 1.0);
> > -             weston_matrix_multiply(&output->matrix, &modelview);
> > +             weston_matrix_translate(&output->matrix,
-output->zoom.trans_x,
> > +                                     output->zoom.trans_y, 0);
> > +             weston_matrix_scale(&output->matrix, magnification,
> > +                                 magnification, 1.0);
> >       }
> >
> >       output->dirty = 0;
>
> About time someone did this! :-D
> Yes, please.

I'll second that.
--Jason Ekstrand

>
>
> Thanks,
> pq
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