[gthumb] cairo scale: fixed lanczos interpolation, added mitchell-netravali

[Paolo Bacchilega <paobac src gnome org>]

commit 05bcda3f7ead13b46b669849b461eea2894d8f64
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Thu Sep 5 20:30:00 2013 +0200

    cairo scale: fixed lanczos interpolation, added mitchell-netravali

 extensions/file_tools/gth-file-tool-resize.c |    2 +-
 gthumb/cairo-scale.c                         |  117 ++++++++++++++++++--------
 gthumb/cairo-scale.h                         |    6 +-
 3 files changed, 85 insertions(+), 40 deletions(-)
---
diff --git a/extensions/file_tools/gth-file-tool-resize.c b/extensions/file_tools/gth-file-tool-resize.c
index 0ce4eb0..ada52d2 100644
--- a/extensions/file_tools/gth-file-tool-resize.c
+++ b/extensions/file_tools/gth-file-tool-resize.c
@@ -671,7 +671,7 @@ gth_file_tool_resize_get_options (GthFileTool *base)
        gtk_combo_box_set_active (GTK_COMBO_BOX (self->priv->ratio_combobox),
                                  g_settings_get_enum (self->priv->settings, PREF_RESIZE_ASPECT_RATIO));
 
-       gth_image_viewer_set_zoom_quality (GTH_IMAGE_VIEWER (viewer), GTH_ZOOM_QUALITY_LOW);
+       gth_image_viewer_set_zoom_quality (GTH_IMAGE_VIEWER (viewer), GTH_ZOOM_QUALITY_HIGH);
 
        return options;
 }
diff --git a/gthumb/cairo-scale.c b/gthumb/cairo-scale.c
index e267514..9f293b9 100644
--- a/gthumb/cairo-scale.c
+++ b/gthumb/cairo-scale.c
@@ -32,7 +32,7 @@
 #define EPSILON ((ScaleReal) 1.0e-16)
 
 
-typedef float ScaleReal;
+typedef double ScaleReal;
 typedef ScaleReal (*weight_func_t) (ScaleReal distance);
 
 
@@ -202,7 +202,7 @@ sinc_fast (ScaleReal x)
 {
        if (x > 4.0) {
                const ScaleReal alpha = G_PI * x;
-               return sin (alpha) / alpha;
+               return sin ((double) alpha) / alpha;
        }
 
        {
@@ -213,33 +213,60 @@ sinc_fast (ScaleReal x)
                const ScaleReal xx = x*x;
 
                /*
-                * Maximum absolute relative error 6.3e-6 < 1/2^17.
+                * Maximum absolute relative error 1.2e-12 < 1/2^39.
                 */
-               const ScaleReal c0 = 0.173610016489197553621906385078711564924e-2L;
-               const ScaleReal c1 = -0.384186115075660162081071290162149315834e-3L;
-               const ScaleReal c2 = 0.393684603287860108352720146121813443561e-4L;
-               const ScaleReal c3 = -0.248947210682259168029030370205389323899e-5L;
-               const ScaleReal c4 = 0.107791837839662283066379987646635416692e-6L;
-               const ScaleReal c5 = -0.324874073895735800961260474028013982211e-8L;
-               const ScaleReal c6 = 0.628155216606695311524920882748052490116e-10L;
-               const ScaleReal c7 = -0.586110644039348333520104379959307242711e-12L;
-               const ScaleReal p = c0+xx*(c1+xx*(c2+xx*(c3+xx*(c4+xx*(c5+xx*(c6+xx*c7))))));
 
-               return (xx-1.0)*(xx-4.0)*(xx-9.0)*(xx-16.0)*p;
+               const ScaleReal c0 = 0.173611111110910715186413700076827593074e-2L;
+               const ScaleReal c1 = -0.289105544717893415815859968653611245425e-3L;
+               const ScaleReal c2 = 0.206952161241815727624413291940849294025e-4L;
+               const ScaleReal c3 = -0.834446180169727178193268528095341741698e-6L;
+               const ScaleReal c4 = 0.207010104171026718629622453275917944941e-7L;
+               const ScaleReal c5 = -0.319724784938507108101517564300855542655e-9L;
+               const ScaleReal c6 = 0.288101675249103266147006509214934493930e-11L;
+               const ScaleReal c7 = -0.118218971804934245819960233886876537953e-13L;
+               const ScaleReal p = c0+xx*(c1+xx*(c2+xx*(c3+xx*(c4+xx*(c5+xx*(c6+xx*c7))))));
+               const ScaleReal d0 = 1.0L;
+               const ScaleReal d1 = 0.547981619622284827495856984100563583948e-1L;
+               const ScaleReal d2 = 0.134226268835357312626304688047086921806e-2L;
+               const ScaleReal d3 = 0.178994697503371051002463656833597608689e-4L;
+               const ScaleReal d4 = 0.114633394140438168641246022557689759090e-6L;
+               const ScaleReal q = d0+xx*(d1+xx*(d2+xx*(d3+xx*d4)));
+
+               return ((xx-1.0)*(xx-4.0)*(xx-9.0)*(xx-16.0)/q*p);
        }
 }
 
 
+static ScaleReal inline
+mitchell_netravali (ScaleReal x)
+{
+       ScaleReal xx;
+
+       if (x >= 2.0)
+               return 0.0;
+
+       xx = x * x;
+       if ((x >= 0.0) && (x < 1.0))
+               x  = (21 * xx * x) - (36 * xx) + 16;
+       else /* (x >= 1.0) && (x < 2.0) */
+               x  = (-7 * xx * x) + (36 * xx) - (60 * x) + 32;
+
+       return x / 18.0;
+}
+
+
 static struct {
        weight_func_t weight_func;
        ScaleReal     support;
 }
 const filters[N_SCALE_FILTERS] = {
-       { box,           .0 },
-       { box,           .5 },
-       { triangle,     1.0 },
-       { cubic,        2.0 },
-       { sinc_fast,    3.0 }
+       { box,                  .0 },
+       { box,                  .5 },
+       { triangle,             1.0 },
+       { cubic,                2.0 },
+       { sinc_fast,            2.0 },
+       { sinc_fast,            3.0 },
+       { mitchell_netravali,   2.0 }
 };
 
 
@@ -256,19 +283,26 @@ typedef struct {
 } resize_filter_t;
 
 
+static void
+resize_filter_set_type (resize_filter_t *resize_filter,
+                       scale_filter_t   filter_type)
+{
+       resize_filter->weight_func = filters[filter_type].weight_func;
+       resize_filter->support = filters[filter_type].support;
+}
+
+
 static resize_filter_t *
-resize_filter_create (scale_filter_t  filter_type,
-                     GthAsyncTask   *task)
+resize_filter_create (GthAsyncTask *task)
 {
        resize_filter_t *resize_filter;
 
        resize_filter = g_new (resize_filter_t, 1);
-       resize_filter->weight_func = filters[filter_type].weight_func;
-       resize_filter->support = filters[filter_type].support;
        resize_filter->task = task;
        resize_filter->total_lines = 0;
        resize_filter->processed_lines = 0;
        resize_filter->cancelled = FALSE;
+       resize_filter_set_type (resize_filter, SCALE_FILTER_TRIANGLE);
 
        return resize_filter;
 }
@@ -285,12 +319,20 @@ static ScaleReal inline
 resize_filter_get_weight (resize_filter_t *resize_filter,
                          ScaleReal        distance)
 {
-       ScaleReal scale = 1.0;
+       ScaleReal window = 1.0;
 
-       if (resize_filter->weight_func == sinc_fast)
-               scale = resize_filter->weight_func (fabs (distance));
+       if (resize_filter->weight_func == sinc_fast) {
+               ScaleReal x = fabs (distance);
 
-       return scale * resize_filter->weight_func (fabs (distance));
+               if (x == 0)
+                       window = 1.0;
+               else if ((x > 0) && (x < resize_filter->support))
+                       window = resize_filter->weight_func (x / resize_filter->support);
+               else
+                       window = 0.0;
+       }
+
+       return window * resize_filter->weight_func (fabs (distance));
 }
 
 
@@ -332,8 +374,10 @@ horizontal_scale_transpose (cairo_surface_t *image,
 
        scale = MAX ((ScaleReal) 1.0 / scale_factor + EPSILON, 1.0);
        support = scale * resize_filter_get_support (resize_filter);
-       if (support < 0.5)
+       if (support < 0.5) {
                support = 0.5;
+               scale = 1.0;
+       }
 
        image_width = cairo_image_surface_get_width (image);
        scaled_width = cairo_image_surface_get_width (scaled);
@@ -364,11 +408,9 @@ horizontal_scale_transpose (cairo_surface_t *image,
                        gth_async_task_set_data (resize_filter->task, NULL, NULL, &progress);
                }
 
-               bisect = ((ScaleReal) y + 0.5) / scale + EPSILON;
-               start = bisect - support + 0.5;
-               start = CLAMP (start, 0, image_width - 1);
-               stop = bisect + support + 0.5;
-               stop = CLAMP (stop, 0, image_width - 1);
+               bisect = ((ScaleReal) y + 0.5) / scale_factor + EPSILON;
+               start = MAX (bisect - support + 0.5, 0);
+               stop = MIN (bisect + support + 0.5, (ScaleReal) image_width);
 
                density = 0.0;
                for (n = 0; n < stop - start; n++) {
@@ -432,10 +474,10 @@ horizontal_scale_transpose (cairo_surface_t *image,
                                p_src_pixel += 4;
                        }
 
-                       p_dest_pixel[CAIRO_RED] = CLAMP_PIXEL (r+0.5);
-                       p_dest_pixel[CAIRO_GREEN] = CLAMP_PIXEL (g+0.5);
-                       p_dest_pixel[CAIRO_BLUE] = CLAMP_PIXEL (b+0.5);
-                       p_dest_pixel[CAIRO_ALPHA] = CLAMP_PIXEL (a+0.5);
+                       p_dest_pixel[CAIRO_RED] = CLAMP_PIXEL (r + 0.5);
+                       p_dest_pixel[CAIRO_GREEN] = CLAMP_PIXEL (g + 0.5);
+                       p_dest_pixel[CAIRO_BLUE] = CLAMP_PIXEL (b + 0.5);
+                       p_dest_pixel[CAIRO_ALPHA] = CLAMP_PIXEL (a + 0.5);
 
 #endif /* HAVE_VECTOR_OPERATIONS */
 
@@ -486,7 +528,8 @@ _cairo_image_surface_scale (cairo_surface_t  *image,
                g_once_init_leave (&coefficients_initialization, 1);
        }
 
-       resize_filter = resize_filter_create (filter, task);
+       resize_filter = resize_filter_create (task);
+       resize_filter_set_type (resize_filter, filter);
        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 1533ebc..dd85c0a 100644
--- a/gthumb/cairo-scale.h
+++ b/gthumb/cairo-scale.h
@@ -36,11 +36,13 @@ typedef enum /*< skip >*/ {
        SCALE_FILTER_BOX,
        SCALE_FILTER_TRIANGLE,
        SCALE_FILTER_CUBIC,
-       SCALE_FILTER_LANCZOS_3,
+       SCALE_FILTER_LANCZOS2,
+       SCALE_FILTER_LANCZOS3,
+       SCALE_FILTER_MITCHELL_NETRAVALI,
        N_SCALE_FILTERS,
 
        SCALE_FILTER_FAST = SCALE_FILTER_POINT,
-       SCALE_FILTER_BEST = SCALE_FILTER_LANCZOS_3,
+       SCALE_FILTER_BEST = SCALE_FILTER_LANCZOS3,
        SCALE_FILTER_GOOD = SCALE_FILTER_TRIANGLE
 } scale_filter_t;