app: add GimpMeter widget

GimpMeter visualizes a set of values that change over time.  It
consists of a gauge, showing the most-recent sampled values, a
history graph, showing a plot of the values over time, and an LED,
which can be used as a boolean indicator for some condition.

GimpMeter is used in the dashboard dockable, added in the next
commit.

app/widgets/Makefile.am

@@ -253,6 +253,8 @@ libappwidgets_a_sources = \
 	gimpmessagebox.h		\
 	gimpmessagedialog.c		\
 	gimpmessagedialog.h		\
+	gimpmeter.c			\
+	gimpmeter.h			\
 	gimpnavigationview.c		\
 	gimpnavigationview.h		\
 	gimpopendialog.c		\

app/widgets/gimpmeter.h

@@ -0,0 +1,103 @@
+/* GIMP - The GNU Image Manipulation Program
+ * Copyright (C) 1995 Spencer Kimball and Peter Mattis
+ *
+ * gimpmeter.h
+ * Copyright (C) 2017 Ell
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __GIMP_METER_H__
+#define __GIMP_METER_H__
+
+
+#define GIMP_TYPE_METER            (gimp_meter_get_type ())
+#define GIMP_METER(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GIMP_TYPE_METER, GimpMeter))
+#define GIMP_METER_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GIMP_TYPE_METER, GimpMeterClass))
+#define GIMP_IS_METER(obj)         (G_TYPE_CHECK_INSTANCE_TYPE (obj, GIMP_TYPE_METER))
+#define GIMP_IS_METER_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GIMP_TYPE_METER))
+#define GIMP_METER_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GIMP_TYPE_METER, GimpMeterClass))
+
+
+typedef struct _GimpMeterPrivate GimpMeterPrivate;
+typedef struct _GimpMeterClass   GimpMeterClass;
+
+struct _GimpMeter
+{
+  GtkWidget         parent_instance;
+
+  GimpMeterPrivate *priv;
+};
+
+struct _GimpMeterClass
+{
+  GtkWidgetClass  parent_class;
+};
+
+
+GType           gimp_meter_get_type               (void) G_GNUC_CONST;
+
+GtkWidget     * gimp_meter_new                    (gint           n_values);
+
+void            gimp_meter_set_size               (GimpMeter     *meter,
+                                                   gint           size);
+gint            gimp_meter_get_size               (GimpMeter     *meter);
+
+void            gimp_meter_set_refresh_rate       (GimpMeter     *meter,
+                                                   gdouble        rate);
+gdouble         gimp_meter_get_refresh_rate       (GimpMeter     *meter);
+
+void            gimp_meter_set_range              (GimpMeter     *meter,
+                                                   gdouble        min,
+                                                   gdouble        max);
+gdouble         gimp_meter_get_range_min          (GimpMeter     *meter);
+gdouble         gimp_meter_get_range_max          (GimpMeter     *meter);
+
+void            gimp_meter_set_n_values           (GimpMeter     *meter,
+                                                   gint           n_values);
+gint            gimp_meter_get_n_values           (GimpMeter     *meter);
+
+void            gimp_meter_set_color              (GimpMeter     *meter,
+                                                   gint           i,
+                                                   const GimpRGB *color);
+const GimpRGB * gimp_meter_get_color              (GimpMeter     *meter,
+                                                   gint           i);
+
+void            gimp_meter_set_history_visible    (GimpMeter     *meter,
+                                                   gboolean       visible);
+gboolean        gimp_meter_get_history_visible    (GimpMeter     *meter);
+
+void            gimp_meter_set_history_duration   (GimpMeter     *meter,
+                                                   gdouble        duration);
+gdouble         gimp_meter_get_history_duration   (GimpMeter     *meter);
+
+void            gimp_meter_set_history_resolution (GimpMeter     *meter,
+                                                   gdouble        resolution);
+gdouble         gimp_meter_get_history_resolution (GimpMeter     *meter);
+
+void            gimp_meter_clear_history          (GimpMeter     *meter);
+
+void            gimp_meter_add_sample             (GimpMeter     *meter,
+                                                   const gdouble *sample);
+
+void            gimp_meter_set_led_visible        (GimpMeter     *meter,
+                                                   gboolean       visible);
+gboolean        gimp_meter_get_led_visible        (GimpMeter     *meter);
+
+void            gimp_meter_set_led_color          (GimpMeter     *meter,
+                                                   const GimpRGB *color);
+const GimpRGB * gimp_meter_get_led_color          (GimpMeter     *meter);
+
+
+#endif /* __GIMP_METER_H__ */

app/widgets/widgets-types.h

@@ -202,6 +202,7 @@ typedef struct _GimpLanguageStore            GimpLanguageStore;
 typedef struct _GimpLayerModeBox             GimpLayerModeBox;
 typedef struct _GimpLayerModeComboBox        GimpLayerModeComboBox;
 typedef struct _GimpMessageBox               GimpMessageBox;
+typedef struct _GimpMeter                    GimpMeter;
 typedef struct _GimpOverlayBox               GimpOverlayBox;
 typedef struct _GimpPickableButton           GimpPickableButton;
 typedef struct _GimpPickablePopup            GimpPickablePopup;