[Pixman] [PATCH 08/15] pixman-image: Added enable-gnuplot config to view filters in gnuplot
spitzak at gmail.com
spitzak at gmail.com
Wed Aug 31 05:03:08 UTC 2016
From: Bill Spitzak <spitzak at gmail.com>
If enable-gnuplot is configured, 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
Changes by Søren: Rewrote the pixman-filter.c part to
- make it generate correct coordinates
- add a comment on how coordinates are generated
- in rounding.txt, add a ceil() variant of the first-sample
formula
- make the gnuplot output slightly prettier
v7: First time this ability was included
v8: Use config option
Moved code to the filter generator
Modified scale demo to not call filter generator a second time.
v10: Only print if successful generation of plots
Use #ifdef, not #if
v11: small whitespace fixes
v12: output range from -width/2 to width/2 and include y==0, to avoid misleading plots
for subsample_bits==0 and for box filters which may have no small values.
Signed-off-by: Bill Spitzak <spitzak at gmail.com>
---
configure.ac | 13 ++++++
pixman/pixman-filter.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++++
pixman/rounding.txt | 1 +
3 files changed, 131 insertions(+)
diff --git a/configure.ac b/configure.ac
index 6b2134e..e833e45 100644
--- a/configure.ac
+++ b/configure.ac
@@ -834,6 +834,19 @@ fi
AC_SUBST(PIXMAN_TIMERS)
dnl ===================================
+dnl gnuplot
+
+AC_ARG_ENABLE(gnuplot,
+ [AC_HELP_STRING([--enable-gnuplot],
+ [enable output of filters that can be piped to gnuplot [default=no]])],
+ [enable_gnuplot=$enableval], [enable_gnuplot=no])
+
+if test $enable_gnuplot = yes ; then
+ AC_DEFINE(PIXMAN_GNUPLOT, 1, [enable output that can be piped to gnuplot])
+fi
+AC_SUBST(PIXMAN_GNUPLOT)
+
+dnl ===================================
dnl GTK+
AC_ARG_ENABLE(gtk,
diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
index b2bf53f..aa7bb80 100644
--- a/pixman/pixman-filter.c
+++ b/pixman/pixman-filter.c
@@ -297,6 +297,119 @@ create_1d_filter (int *width,
return params;
}
+#ifdef PIXMAN_GNUPLOT
+
+/* If enable-gnuplot is configured, 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
+ */
+static void
+gnuplot_filter (int width, int n_phases, const pixman_fixed_t* p)
+{
+ double step;
+ int i, j;
+ int first;
+
+ step = 1.0 / n_phases;
+
+ printf ("set style line 1 lc rgb '#0060ad' lt 1 lw 0.5 pt 7 pi 1 ps 0.5\n");
+ printf ("plot [x=%g:%g] '-' with linespoints ls 1\n", -width*0.5, width*0.5);
+ /* Print a point at the origin so that y==0 line is included: */
+ printf ("0 0\n\n");
+
+ /* The position of the first sample of the phase corresponding to
+ * frac is given by:
+ *
+ * ceil (frac - width / 2.0 - 0.5) + 0.5 - frac
+ *
+ * We have to find the frac that minimizes this expression.
+ *
+ * For odd widths, we have
+ *
+ * ceil (frac - width / 2.0 - 0.5) + 0.5 - frac
+ * = ceil (frac) + K - frac
+ * = 1 + K - frac
+ *
+ * for some K, so this is minimized when frac is maximized and
+ * strictly growing with frac. So for odd widths, we can simply
+ * start at the last phase and go backwards.
+ *
+ * For even widths, we have
+ *
+ * ceil (frac - width / 2.0 - 0.5) + 0.5 - frac
+ * = ceil (frac - 0.5) + K - frac
+ *
+ * The graph for this function (ignoring K) looks like this:
+ *
+ * 0.5
+ * | |\
+ * | | \
+ * | | \
+ * 0 | | \
+ * |\ |
+ * | \ |
+ * | \ |
+ * -0.5 | \|
+ * ---------------------------------
+ * 0 0.5 1
+ *
+ * So in this case we need to start with the phase whose frac is
+ * less than, but as close as possible to 0.5, then go backwards
+ * until we hit the first phase, then wrap around to the last
+ * phase and continue backwards.
+ *
+ * Which phase is as close as possible 0.5? The locations of the
+ * sampling point corresponding to the kth phase is given by
+ * 1/(2 * n_phases) + k / n_phases:
+ *
+ * 1/(2 * n_phases) + k / n_phases = 0.5
+ *
+ * from which it follows that
+ *
+ * k = (n_phases - 1) / 2
+ *
+ * rounded down is the phase in question.
+ */
+ if (width & 1)
+ first = n_phases - 1;
+ else
+ first = (n_phases - 1) / 2;
+
+ for (j = 0; j < width; ++j)
+ {
+ for (i = 0; i < n_phases; ++i)
+ {
+ int phase = first - i;
+ double frac, pos;
+
+ if (phase < 0)
+ phase = n_phases + phase;
+
+ frac = step / 2.0 + phase * step;
+ pos = ceil (frac - width / 2.0 - 0.5) + 0.5 - frac + j;
+
+ printf ("%g %g\n",
+ pos,
+ pixman_fixed_to_double (*(p + phase * width + j)));
+ }
+ }
+
+ printf ("e\n");
+ fflush (stdout);
+}
+
+#endif
+
/* Create the parameter list for a SEPARABLE_CONVOLUTION filter
* with the given kernels and scale parameters
*/
@@ -346,5 +459,9 @@ out:
free (horz);
free (vert);
+#ifdef PIXMAN_GNUPLOT
+ gnuplot_filter(width, subsample_x, params + 4);
+#endif
+
return params;
}
diff --git a/pixman/rounding.txt b/pixman/rounding.txt
index b52b084..1c00019 100644
--- a/pixman/rounding.txt
+++ b/pixman/rounding.txt
@@ -160,6 +160,7 @@ which means the contents of the matrix corresponding to (frac) should
contain width samplings of the function, with the first sample at:
floor (frac - (width - 1) / 2.0 - e) + 0.5 - frac
+ = ceil (frac - width / 2.0 - 0.5) + 0.5 - frac
This filter is called separable because each of the k x k convolution
matrices is specified with two k-wide vectors, one for each dimension,
--
1.9.1
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