[gimp] Bug 735895 - Precision Conversion "Dithering" dialog

[Michael Natterer <mitch src gnome org>]

commit 91df48ef3708227ba2f2474b054baf62e2c7699a
Author: Michael Natterer <mitch gimp org>
Date:   Wed Nov 9 13:10:56 2016 +0100

    Bug 735895 - Precision Conversion "Dithering" dialog
    
    Disable the convert precision dialog's dithering controls when
    converting to higher bit depths o to anything > 16 bit.
    
    Make sure the disabled dithering widgets always says "None", which
    implies duplicating the bit depth checking logic in both the dialog
    and its callback, in order to protect the values in GimpDialogConfig
    from being overwritten by NONE.

 app/actions/image-commands.c           |   31 ++++++++++++++
 app/dialogs/convert-precision-dialog.c |   72 ++++++++++++++++++++-----------
 2 files changed, 77 insertions(+), 26 deletions(-)
---
diff --git a/app/actions/image-commands.c b/app/actions/image-commands.c
index 890c641..9f49cfa 100644
--- a/app/actions/image-commands.c
+++ b/app/actions/image-commands.c
@@ -1165,6 +1165,10 @@ image_convert_precision_callback (GtkWidget        *dialog,
   GimpDialogConfig *config   = GIMP_DIALOG_CONFIG (image->gimp->config);
   GimpProgress     *progress = user_data;
   const gchar      *enum_desc;
+  const Babl       *old_format;
+  const Babl       *new_format;
+  gint              old_bits;
+  gint              new_bits;
 
   g_object_set (config,
                 "image-convert-precision-layer-dither-method",
@@ -1175,6 +1179,33 @@ image_convert_precision_callback (GtkWidget        *dialog,
                 channel_dither_method,
                 NULL);
 
+  /*  we do the same dither method checks here *and* in the dialog,
+   *  because the dialog leaves the passed dither methods untouched if
+   *  dithering is disabled and passes the original values to the
+   *  callback, in order not to change the values saved in
+   *  GimpDialogConfig.
+   */
+
+  /* random formats with the right precision */
+  old_format = gimp_image_get_layer_format (image, FALSE);
+  new_format = gimp_babl_format (GIMP_RGB, precision, FALSE);
+
+  old_bits = (babl_format_get_bytes_per_pixel (old_format) * 8 /
+              babl_format_get_n_components (old_format));
+  new_bits = (babl_format_get_bytes_per_pixel (new_format) * 8 /
+              babl_format_get_n_components (new_format));
+
+  if (new_bits >= old_bits || new_bits > 16)
+    {
+      /*  don't dither if we are converting to a higher bit depth,
+       *  or to more than 16 bits (gegl:color-reduction only does
+       *  16 bits).
+       */
+      layer_dither_method      = GEGL_DITHER_NONE;
+      text_layer_dither_method = GEGL_DITHER_NONE;
+      channel_dither_method    = GEGL_DITHER_NONE;
+    }
+
   gimp_enum_get_value (GIMP_TYPE_PRECISION, precision,
                        NULL, NULL, &enum_desc, NULL);
 
diff --git a/app/dialogs/convert-precision-dialog.c b/app/dialogs/convert-precision-dialog.c
index 0ecbc1d..ed50fe2 100644
--- a/app/dialogs/convert-precision-dialog.c
+++ b/app/dialogs/convert-precision-dialog.c
@@ -46,7 +46,6 @@ struct _ConvertDialog
   GimpImage                    *image;
   GimpComponentType             component_type;
   gboolean                      linear;
-  gint                          bits;
   GeglDitherMethod              layer_dither_method;
   GeglDitherMethod              text_layer_dither_method;
   GeglDitherMethod              channel_dither_method;
@@ -89,8 +88,11 @@ convert_precision_dialog_new (GimpImage                    *image,
   GtkSizeGroup  *size_group;
   const gchar   *enum_desc;
   gchar         *blurb;
-  const Babl    *format;
-  gint           bits;
+  const Babl    *old_format;
+  const Babl    *new_format;
+  gint           old_bits;
+  gint           new_bits;
+  gboolean       dither;
   gboolean       linear;
 
   g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
@@ -98,22 +100,29 @@ convert_precision_dialog_new (GimpImage                    *image,
   g_return_val_if_fail (GTK_IS_WIDGET (parent), NULL);
   g_return_val_if_fail (callback != NULL, NULL);
 
-  /* a random format with precision */
-  format = gimp_babl_format (GIMP_RGB,
-                             gimp_babl_precision (component_type, FALSE),
-                             FALSE);
-  bits   = (babl_format_get_bytes_per_pixel (format) * 8 /
-            babl_format_get_n_components (format));
+  /* random formats with the right precision */
+  old_format = gimp_image_get_layer_format (image, FALSE);
+  new_format = gimp_babl_format (GIMP_RGB,
+                                 gimp_babl_precision (component_type, FALSE),
+                                 FALSE);
 
-  linear = gimp_babl_format_get_linear (gimp_image_get_layer_format (image,
-                                                                     FALSE));
+  old_bits = (babl_format_get_bytes_per_pixel (old_format) * 8 /
+              babl_format_get_n_components (old_format));
+  new_bits = (babl_format_get_bytes_per_pixel (new_format) * 8 /
+              babl_format_get_n_components (new_format));
+
+  /*  don't dither if we are converting to a higher bit depth, or to
+   *  more than 16 bits (gegl:color-reduction only does 16 bits).
+   */
+  dither = (new_bits < old_bits && new_bits <= 16);
+
+  linear = gimp_babl_format_get_linear (old_format);
 
   private = g_slice_new0 (ConvertDialog);
 
   private->image                    = image;
   private->component_type           = component_type;
   private->linear                   = linear;
-  private->bits                     = bits;
   private->layer_dither_method      = layer_dither_method;
   private->text_layer_dither_method = text_layer_dither_method;
   private->channel_dither_method    = channel_dither_method;
@@ -177,8 +186,7 @@ convert_precision_dialog_new (GimpImage                    *image,
   gtk_container_add (GTK_CONTAINER (frame), vbox);
   gtk_widget_show (vbox);
 
-  /* gegl:color-reduction only does 16 bits */
-  gtk_widget_set_sensitive (vbox, bits <= 16);
+  gtk_widget_set_sensitive (vbox, dither);
 
   size_group = gtk_size_group_new (GTK_SIZE_GROUP_HORIZONTAL);
 
@@ -199,10 +207,14 @@ convert_precision_dialog_new (GimpImage                    *image,
   gtk_box_pack_start (GTK_BOX (hbox), combo, TRUE, TRUE, 0);
   gtk_widget_show (combo);
 
-  gimp_int_combo_box_connect (GIMP_INT_COMBO_BOX (combo),
-                              private->layer_dither_method,
-                              G_CALLBACK (gimp_int_combo_box_get_active),
-                              &private->layer_dither_method);
+  if (dither)
+    gimp_int_combo_box_connect (GIMP_INT_COMBO_BOX (combo),
+                                private->layer_dither_method,
+                                G_CALLBACK (gimp_int_combo_box_get_active),
+                                &private->layer_dither_method);
+  else
+    gimp_int_combo_box_set_active (GIMP_INT_COMBO_BOX (combo),
+                                   GEGL_DITHER_NONE);
 
   /*  text layers  */
 
@@ -221,10 +233,14 @@ convert_precision_dialog_new (GimpImage                    *image,
   gtk_box_pack_start (GTK_BOX (hbox), combo, TRUE, TRUE, 0);
   gtk_widget_show (combo);
 
-  gimp_int_combo_box_connect (GIMP_INT_COMBO_BOX (combo),
-                              private->text_layer_dither_method,
-                              G_CALLBACK (gimp_int_combo_box_get_active),
-                              &private->text_layer_dither_method);
+  if (dither)
+    gimp_int_combo_box_connect (GIMP_INT_COMBO_BOX (combo),
+                                private->text_layer_dither_method,
+                                G_CALLBACK (gimp_int_combo_box_get_active),
+                                &private->text_layer_dither_method);
+  else
+    gimp_int_combo_box_set_active (GIMP_INT_COMBO_BOX (combo),
+                                   GEGL_DITHER_NONE);
 
   gimp_help_set_help_data (combo,
                            _("Dithering text layers will make them uneditable"),
@@ -247,10 +263,14 @@ convert_precision_dialog_new (GimpImage                    *image,
   gtk_box_pack_start (GTK_BOX (hbox), combo, TRUE, TRUE, 0);
   gtk_widget_show (combo);
 
-  gimp_int_combo_box_connect (GIMP_INT_COMBO_BOX (combo),
-                              private->channel_dither_method,
-                              G_CALLBACK (gimp_int_combo_box_get_active),
-                              &private->channel_dither_method);
+  if (dither)
+    gimp_int_combo_box_connect (GIMP_INT_COMBO_BOX (combo),
+                                private->channel_dither_method,
+                                G_CALLBACK (gimp_int_combo_box_get_active),
+                                &private->channel_dither_method);
+  else
+    gimp_int_combo_box_set_active (GIMP_INT_COMBO_BOX (combo),
+                                   GEGL_DITHER_NONE);
 
   g_object_unref (size_group);