[gthumb] scale: added a CUBIC filter

[Paolo Bacchilega <paobac src gnome org>]

commit f712386e43ebaba5179854d8df49d9be73109251
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sat Jun 29 16:05:09 2013 +0200

    scale: added a CUBIC filter

 gthumb/cairo-scale.c |   37 +++++++++++++++++++++++++++++++++++++
 gthumb/cairo-scale.h |    3 ++-
 2 files changed, 39 insertions(+), 1 deletions(-)
---
diff --git a/gthumb/cairo-scale.c b/gthumb/cairo-scale.c
index ed2e662..e267514 100644
--- a/gthumb/cairo-scale.c
+++ b/gthumb/cairo-scale.c
@@ -166,6 +166,37 @@ triangle (ScaleReal x)
 }
 
 
+static ScaleReal Cubic_P0, Cubic_P2, Cubic_P3;
+static ScaleReal Cubic_Q0, Cubic_Q1, Cubic_Q2, Cubic_Q3;
+static gsize coefficients_initialization = 0;
+
+
+static void
+initialize_coefficients (ScaleReal B,
+                        ScaleReal C)
+{
+       Cubic_P0 = (6.0 - 2.0 * B) / 6.0;
+       /*Cubic_P1 = 0.0;*/
+       Cubic_P2 = (-18.0 + 12.0 * B + 6.0 * C) / 6.0;
+       Cubic_P3 = ( 12.0 - 9.0 * B - 6.0 * C) / 6.0;
+       Cubic_Q0 = (8.0 * B + 24.0 * C) / 6.0;
+       Cubic_Q1 = (-12.0 * B - 48.0 * C) / 6.0;
+       Cubic_Q2 = (6.0 * B + 30.0 * C) / 6.0;
+       Cubic_Q3 = (-1.0 * B - 6.0 * C) / 6.0;
+}
+
+
+static ScaleReal inline
+cubic (ScaleReal x)
+{
+       if (x < 1.0)
+               return Cubic_P0 + x * (x * (Cubic_P2 + x * Cubic_P3));
+       if (x < 2.0)
+               return Cubic_Q0 + x * (Cubic_Q1 + x * (Cubic_Q2 + x * Cubic_Q3));
+       return 0.0;
+}
+
+
 static ScaleReal inline
 sinc_fast (ScaleReal x)
 {
@@ -207,6 +238,7 @@ const filters[N_SCALE_FILTERS] = {
        { box,           .0 },
        { box,           .5 },
        { triangle,     1.0 },
+       { cubic,        2.0 },
        { sinc_fast,    3.0 }
 };
 
@@ -449,6 +481,11 @@ _cairo_image_surface_scale (cairo_surface_t  *image,
        if (scaled == NULL)
                return NULL;
 
+       if (g_once_init_enter (&coefficients_initialization)) {
+               initialize_coefficients (1.0, 0.0);
+               g_once_init_leave (&coefficients_initialization, 1);
+       }
+
        resize_filter = resize_filter_create (filter, task);
        resize_filter->total_lines = scaled_width + scaled_height;
        resize_filter->processed_lines = 0;
diff --git a/gthumb/cairo-scale.h b/gthumb/cairo-scale.h
index 4ce1924..1533ebc 100644
--- a/gthumb/cairo-scale.h
+++ b/gthumb/cairo-scale.h
@@ -32,9 +32,10 @@ G_BEGIN_DECLS
 
 
 typedef enum /*< skip >*/ {
-       SCALE_FILTER_POINT = 0,
+       SCALE_FILTER_POINT,
        SCALE_FILTER_BOX,
        SCALE_FILTER_TRIANGLE,
+       SCALE_FILTER_CUBIC,
        SCALE_FILTER_LANCZOS_3,
        N_SCALE_FILTERS,