[Pixman] [PATCH 03/13] pixman-image: Added GNUPLOT_OUTPUT compile-time option to view filters in gnuplot

[Oded Gabbay]

On Mon, Jan 4, 2016 at 5:12 AM,  <spitzak at gmail.com> wrote:
> From: Bill Spitzak <spitzak at gmail.com>
>
> If GNUPLOT_OUTPUT is set, then you can pipe the output of a pixman-using program
> to gnuplot and get a continuously-updated plot of the horizontal filter. This
> works well with demos/scale to test the filter generation.
>
> The plot is all the different subposition filters shuffled together. This is
> misleading in a few cases:
>
>   IMPULSE.BOX - goes up and down as the subfilters have different numbers of non-zero samples
>   IMPULSE.TRIANGLE - somewhat crooked for the same reason
>   1-wide filters - looks triangular, but a 1-wide box would be more accurate
> ---
>  pixman/pixman-image.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
>
> diff --git a/pixman/pixman-image.c b/pixman/pixman-image.c
> index 1ff1a49..69743c4 100644
> --- a/pixman/pixman-image.c
> +++ b/pixman/pixman-image.c
> @@ -531,6 +531,46 @@ compute_image_info (pixman_image_t *image)
>
>      image->common.flags = flags;
>      image->common.extended_format_code = code;
> +/* If GNUPLOT_OUTPUT is set, then you can pipe the output of a pixman-using program
> + * to gnuplot and get a continuously-updated plot of the horizontal filter. This
> + * works well with demos/scale to test the filter generation.
> + *
> + * The plot is all the different subposition filters shuffled together. This is
> + * misleading in a few cases:
> + *
> + *  IMPULSE.BOX - goes up and down as the subfilters have different numbers of non-zero samples
> + *  IMPULSE.TRIANGLE - somewhat crooked for the same reason
> + *  1-wide filters - looks triangular, but a 1-wide box would be more accurate
> + */
> +/* #define GNUPLOT_OUTPUT 1 */
> +#if GNUPLOT_OUTPUT
> +    if ((flags & FAST_PATH_SEPARABLE_CONVOLUTION_FILTER) && image->common.filter_params) {
> +       const pixman_fixed_t* p = image->common.filter_params;
> +       int width = pixman_fixed_to_int(p[0]);
> +       int samples = 1 << pixman_fixed_to_int(p[2]);
> +       int x,y;
> +       p += 4;
> +       printf("plot '-' with linespoints\n");
> +       printf("%g 0\n", - width * .5);
> +       for (x = 0; x < width; ++x) {
> +           for (y = 0; y < samples; ++y) {
> +               int yy;
> +               if (width & 1)
> +                   yy = y;
> +               else if (y >= samples / 2)
> +                   yy = y - samples / 2;
> +               else
> +                   yy = samples / 2 + y;
> +               printf("%g %g\n",
> +                      x - width * .5 + (y + .5) * (1.0 / samples),
> +                      pixman_fixed_to_double(p[(yy + 1) * width - x - 1]));
> +           }
> +       }
> +       printf("%g 0\n", width * .5);
> +       printf("e\n");
> +       fflush(stdout);
> +    }
> +#endif
>  }
>
>  void
> --
> 1.9.1
>
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I get the big picture of this feature, and it seems useful, but we
need write this according to standards.
I would like to see the following changes:

1. We can do something more nice than a hard-coded #define. Let's add
a flag to configure.ac called "enable-gnuplot-output". For something
similar, see "enable-timers" in configure.ac. The default will be
"no".

2. Take your code and put it in a new function in pixman-utils.c, and
make sure the code inside the function is encompassed with
#ifdef/#endif around it. In case enable-gluplot-output wasn't called,
the function will be an empty function.

3. Call that function from compute_image_info. I guess you will want
to call it only if:
((flags & FAST_PATH_SEPARABLE_CONVOLUTION_FILTER) &&
image->common.filter_params)
is true.
However, we don't need to put #ifdef around the call itself.

I think the above steps will create two patches:
- Step 1&2 should be the first patch (Adding the utility).
- Step 3 should be the second patch (Using the utility).

Is using this is simple as:
./<demo/test binary> | gnuplot     ?

or is it more complicated than that ?
If so, put an example of how to use it in the second commit message.

Thanks,

Oded