libgimpwidgets: don't unnecessarily redraw color previews.

When changing the selected color, we have no reason to redraw the Z preview.
This preview should only be redrawn if the allocation size changed, or if we
change the previewed model or the Z component.

As for the XY preview, it should only be redrawn if the Z value is changed (and
of course, similarly, if the allocation changed or if model or Z component
changed).

libgimpwidgets/gimpcolorselect.c

@@ -149,6 +149,7 @@ struct _GimpColorSelect
   gboolean             z_needs_render;
 
   gdouble              pos[3];
+  gfloat               z_value;
 
   ColorSelectDragMode  drag_mode;
 
@@ -192,8 +193,7 @@ static void   gimp_color_select_set_color       (GimpColorSelector        *selec
                                                             GeglColor                *color);
 static void       gimp_color_select_set_channel            (GimpColorSelector        *selector,
                                                             GimpColorSelectorChannel  channel);
-static void   gimp_color_select_set_model_visible
+static void       gimp_color_select_set_model_visible      (GimpColorSelector        *selector,
-                                                (GimpColorSelector        *selector,
                                                             GimpColorSelectorModel    model,
                                                             gboolean                  visible);
 static void       gimp_color_select_set_format             (GimpColorSelector        *selector,
@@ -279,6 +279,9 @@ static void   gimp_color_select_notify_config      (GimpColorConfig  *config,
                                                             const GParamSpec *pspec,
                                                             GimpColorSelect  *select);
 
+static gfloat     gimp_color_select_get_z_value            (GimpColorSelect *select,
+                                                            GeglColor       *color);
+
 
 G_DEFINE_TYPE (GimpColorSelect, gimp_color_select, GIMP_TYPE_COLOR_SELECTOR)
 
@@ -367,6 +370,7 @@ gimp_color_select_init (GimpColorSelect *select)
   GSList                 *group = NULL;
 
   /* Default values. */
+  select->z_value       = G_MINFLOAT;
   select->z_color_fill  = COLOR_SELECT_HUE;
   select->xy_color_fill = COLOR_SELECT_SATURATION_VALUE;
   select->drag_mode     = DRAG_NONE;
@@ -575,9 +579,22 @@ gimp_color_select_set_color (GimpColorSelector *selector,
                              GeglColor         *color)
 {
   GimpColorSelect       *select       = GIMP_COLOR_SELECT (selector);
+  ColorSelectUpdateType  update_flags = UPDATE_POS;
+  gfloat                 z_value;
 
-  gimp_color_select_update (select,
+  z_value = gimp_color_select_get_z_value (select, color);
-                            UPDATE_POS | UPDATE_XY_COLOR | UPDATE_Z_COLOR);
+
+/* Note: we are not comparing full colors, hence not using
+ * gimp_color_is_perceptually_identical(). It's more of a quick comparison on
+ * whether the Z channel is different enough that we'd want to redraw the XY
+ * preview too.
+ */
+#define GIMP_RGBA_EPSILON 1e-4
+  if (fabs (z_value - select->z_value) > GIMP_RGBA_EPSILON)
+    update_flags |= UPDATE_XY_COLOR;
+#undef GIMP_RGBA_EPSILON
+
+  gimp_color_select_update (select, update_flags);
 }
 
 static void
@@ -1084,6 +1101,7 @@ gimp_color_select_xy_draw (GtkWidget       *widget,
                                 select->xy_color_fill,
                                 color,
                                 select->oog_color);
+      select->z_value = gimp_color_select_get_z_value (select, color);
       select->xy_needs_render = FALSE;
 
       g_object_unref (color);
@@ -1991,3 +2009,43 @@ gimp_color_select_notify_config (GimpColorConfig  *config,
 
   g_object_unref (color);
 }
+
+static gfloat
+gimp_color_select_get_z_value (GimpColorSelect *select,
+                               GeglColor       *color)
+{
+  gint   z_channel = -1;
+  gfloat channels[3];
+
+  switch (select->z_color_fill)
+    {
+    case COLOR_SELECT_RED:
+      z_channel = 0;
+    case COLOR_SELECT_GREEN:
+      z_channel = (z_channel > -1) ? z_channel : 1;
+    case COLOR_SELECT_BLUE:
+      z_channel = (z_channel > -1) ? z_channel : 2;
+      gegl_color_get_pixel (color, rgbf_format, channels);
+      break;
+    case COLOR_SELECT_HUE:
+      z_channel = 0;
+    case COLOR_SELECT_SATURATION:
+      z_channel = (z_channel > -1) ? z_channel : 1;
+    case COLOR_SELECT_VALUE:
+      z_channel = (z_channel > -1) ? z_channel : 2;
+      gegl_color_get_pixel (color, hsvf_format, channels);
+      break;
+    case COLOR_SELECT_LCH_LIGHTNESS:
+      z_channel = 0;
+    case COLOR_SELECT_LCH_CHROMA:
+      z_channel = (z_channel > -1) ? z_channel : 1;
+    case COLOR_SELECT_LCH_HUE:
+      z_channel = (z_channel > -1) ? z_channel : 2;
+      gegl_color_get_pixel (color, babl_format ("CIE LCH(ab) float"), channels);
+      break;
+    default:
+      g_return_val_if_reached (G_MINFLOAT);
+    }
+
+  return channels[z_channel];
+}

libgimpwidgets/gimpwidgets-private.h

@@ -22,9 +22,6 @@
 #ifndef __GIMP_WIDGETS_PRIVATE_H__
 #define __GIMP_WIDGETS_PRIVATE_H__
 
-/* Used to compare similar colors across several widgets. */
-#define GIMP_RGBA_EPSILON 1e-6
-
 
 typedef GeglColor * (* GimpGetColorFunc)      (void);
 typedef void        (* GimpEnsureModulesFunc) (void);