[gimp] plug-ins: help text for special values of kmax.

[Jehan Pagès <jehanp src gnome org>]

commit bfc301e2f9816367f2b80f5bfe293ca8852fddaf
Author: Jehan <jehan girinstud io>
Date:   Sun Jul 23 16:14:16 2017 +0200

    plug-ins: help text for special values of kmax.
    
    Since libwebp 0.6, the keyframe max distance (kmax) has been changed,
    and in particular all special cases are now handled by kmax (it used to
    be weird cases of kmin and kmax intertwined with no logics, for instance
    kmax == 0 AND kmin > 0 would mean all frames are keyframes).
    Now it is much more logical, and kmax == 0 means no keyframes, whereas
    kmax == 1 means all frames are keyframes. See also:
    https://chromium.googlesource.com/webm/libwebp/+/2dc0bdcaeee77ae8b40ff9eb82a9e03a7cecaf04

 plug-ins/file-webp/file-webp-dialog.c |   68 ++++++++++++++++++++++++++------
 1 files changed, 55 insertions(+), 13 deletions(-)
---
diff --git a/plug-ins/file-webp/file-webp-dialog.c b/plug-ins/file-webp/file-webp-dialog.c
index f8916ea..0c8779e 100644
--- a/plug-ins/file-webp/file-webp-dialog.c
+++ b/plug-ins/file-webp/file-webp-dialog.c
@@ -32,11 +32,14 @@
 #include "libgimp/stdplugins-intl.h"
 
 
-static void           save_dialog_toggle_scale   (GtkWidget  *widget,
-                                                  gpointer    data);
+static void           save_dialog_toggle_scale   (GtkWidget     *widget,
+                                                  gpointer       data);
 
-static void           save_dialog_toggle_minsize (GtkWidget  *widget,
-                                                  gpointer    data);
+static void           save_dialog_toggle_minsize (GtkWidget     *widget,
+                                                  gpointer       data);
+
+static void           show_maxkeyframe_hints     (GtkAdjustment *adj,
+                                                  GtkLabel      *label);
 
 
 static void
@@ -55,6 +58,27 @@ save_dialog_toggle_minsize (GtkWidget *widget,
                             ! gtk_toggle_button_get_active (GTK_TOGGLE_BUTTON (widget)));
 }
 
+static void
+show_maxkeyframe_hints (GtkAdjustment *adj,
+                        GtkLabel      *label)
+{
+  gint kmax;
+
+  kmax = (gint) gtk_adjustment_get_value (adj);
+  if (kmax == 0)
+    {
+      gtk_label_set_text (label, _("(no keyframes)"));
+    }
+  else if (kmax == 1)
+    {
+      gtk_label_set_text (label, _("(all frames are keyframes)"));
+    }
+  else
+    {
+      gtk_label_set_text (label, "");
+    }
+}
+
 gboolean
 save_dialog (WebPSaveParams *params,
              gint32          image_ID,
@@ -178,14 +202,16 @@ save_dialog (WebPSaveParams *params,
 
   if (animation_supported)
     {
-      GtkWidget     *animation_box;
-      GtkAdjustment *adj;
-      GtkWidget     *delay;
-      GtkWidget     *hbox;
-      GtkWidget     *label_kf;
-      GtkAdjustment *adj_kf;
-      GtkWidget     *kf_distance;
-      GtkWidget     *hbox_kf;
+      GtkWidget      *animation_box;
+      GtkAdjustment  *adj;
+      GtkWidget      *delay;
+      GtkWidget      *hbox;
+      GtkWidget      *label_kf;
+      GtkAdjustment  *adj_kf;
+      GtkWidget      *kf_distance;
+      GtkWidget      *hbox_kf;
+      PangoAttrList  *attrs;
+      PangoAttribute *attr;
 
       vbox2 = gtk_box_new (GTK_ORIENTATION_VERTICAL, 4);
       gtk_box_pack_start (GTK_BOX (vbox), vbox2, FALSE, FALSE, 0);
@@ -251,7 +277,8 @@ save_dialog (WebPSaveParams *params,
 
       /* key-frame distance entry */
       adj_kf = (GtkAdjustment *) gtk_adjustment_new (params->kf_distance,
-                                                     1, 10000, 1, 10, 0);
+                                                     0.0, 10000.0,
+                                                     1.0, 10.0, 0.0);
       kf_distance = gtk_spin_button_new (adj_kf, 1, 0);
       gtk_spin_button_set_numeric (GTK_SPIN_BUTTON (kf_distance), TRUE);
       gtk_box_pack_start (GTK_BOX (hbox_kf), kf_distance, FALSE, FALSE, 0);
@@ -261,6 +288,21 @@ save_dialog (WebPSaveParams *params,
                         G_CALLBACK (gimp_int_adjustment_update),
                         &params->kf_distance);
 
+      /* Add some hinting text for special values of key-frame distance. */
+      label_kf = gtk_label_new (NULL);
+      gtk_box_pack_start (GTK_BOX (hbox_kf), label_kf, FALSE, FALSE, 0);
+      gtk_widget_show (label_kf);
+
+      attrs = pango_attr_list_new ();
+      attr  = pango_attr_style_new (PANGO_STYLE_ITALIC);
+      pango_attr_list_insert (attrs, attr);
+      gtk_label_set_attributes (GTK_LABEL (label_kf), attrs);
+      pango_attr_list_unref (attrs);
+
+      g_signal_connect (adj_kf, "value-changed",
+                        G_CALLBACK (show_maxkeyframe_hints),
+                        label_kf);
+
       /* minimize-size checkbox */
       toggle_minsize = gtk_check_button_new_with_label (_("Minimize output size (slower)"));