[gimp] app: allow picking layer in paint tools on alt-click.

[Jehan <jehanp src gnome org>]

commit 3b59e6f61ef44b9400865031871c5387840cd71e
Author: Jehan <jehan girinstud io>
Date:   Sat Dec 15 22:55:12 2018 +0100

    app: allow picking layer in paint tools on alt-click.
    
    When working with a lot of layers, it is common to have to switch easily
    between layers. And having to go back to the layer list is annoying and
    also sometimes not practical at all when you can't find easily the right
    layer. This is a first step in an experiment for such a feature, worked
    together with Aryeom as advisor (and originator of the feature idea).
    For now I apply this only to paint tools, though we are considering
    having it as a generic modifier too, working whatever the tool. Yet we
    wouldn't be able to use alt-left click (as it is used already in some
    tools).
    How it works is simply that in any paint tool, alt-click allows to
    switch to the topmost layer having a visible pixel at the clicked
    position.

 app/tools/gimppainttool.c | 61 +++++++++++++++++++++++++++++++++++++++++------
 app/tools/gimppainttool.h |  2 ++
 2 files changed, 56 insertions(+), 7 deletions(-)
---
diff --git a/app/tools/gimppainttool.c b/app/tools/gimppainttool.c
index b303831019..c208e3ae98 100644
--- a/app/tools/gimppainttool.c
+++ b/app/tools/gimppainttool.c
@@ -32,6 +32,7 @@
 #include "core/gimpdrawable.h"
 #include "core/gimperror.h"
 #include "core/gimpimage.h"
+#include "core/gimpimage-pick-item.h"
 #include "core/gimplayer.h"
 #include "core/gimppaintinfo.h"
 #include "core/gimpprojection.h"
@@ -266,7 +267,18 @@ gimp_paint_tool_button_press (GimpTool            *tool,
   gboolean          constrain;
   GError           *error = NULL;
 
-  if (gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)))
+  if (paint_tool->picking_layer)
+    {
+      GimpLayer *layer;
+
+      layer = gimp_image_pick_layer (image,
+                                     (gint) coords->x,
+                                     (gint) coords->y);
+      if (layer && layer != gimp_image_get_active_layer (image))
+        gimp_image_set_active_layer (image, layer);
+      return;
+    }
+  else if (gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)))
     {
       GIMP_TOOL_CLASS (parent_class)->button_press (tool, coords, time, state,
                                                     press_type, display);
@@ -365,7 +377,7 @@ gimp_paint_tool_button_release (GimpTool              *tool,
   GimpImage        *image      = gimp_display_get_image (display);
   gboolean          cancel;
 
-  if (gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)))
+  if (gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)) || paint_tool->picking_layer)
     {
       GIMP_TOOL_CLASS (parent_class)->button_release (tool, coords, time,
                                                       state, release_type,
@@ -400,7 +412,7 @@ gimp_paint_tool_motion (GimpTool         *tool,
 
   GIMP_TOOL_CLASS (parent_class)->motion (tool, coords, time, state, display);
 
-  if (gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)))
+  if (gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)) || paint_tool->picking_layer)
     return;
 
   gimp_paint_tool_paint_motion (paint_tool, coords, time);
@@ -463,6 +475,14 @@ gimp_paint_tool_modifier_key (GimpTool        *tool,
             }
         }
     }
+  if (! gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)) &&
+      ! paint_tool->draw_line)
+    {
+      if ((state & gimp_get_all_modifiers_mask ()) == GDK_MOD1_MASK)
+        paint_tool->picking_layer = TRUE;
+      else
+        paint_tool->picking_layer = FALSE;
+    }
 }
 
 static void
@@ -472,18 +492,40 @@ gimp_paint_tool_cursor_update (GimpTool         *tool,
                                GimpDisplay      *display)
 {
   GimpPaintTool      *paint_tool = GIMP_PAINT_TOOL (tool);
+  GimpToolCursorType  tool_cursor;
   GimpCursorModifier  modifier;
   GimpCursorModifier  toggle_modifier;
+  GimpToolCursorType  old_tool_cursor;
   GimpCursorModifier  old_modifier;
   GimpCursorModifier  old_toggle_modifier;
 
+  tool_cursor     = tool->control->tool_cursor;
   modifier        = tool->control->cursor_modifier;
   toggle_modifier = tool->control->toggle_cursor_modifier;
 
+  old_tool_cursor     = tool_cursor;
   old_modifier        = modifier;
   old_toggle_modifier = toggle_modifier;
 
-  if (! gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)))
+  if (paint_tool->picking_layer)
+    {
+      GimpImage *image = gimp_display_get_image (display);
+      GimpLayer *layer;
+
+      layer = gimp_image_pick_layer (image,
+                                     (gint) coords->x,
+                                     (gint) coords->y);
+
+      modifier = GIMP_CURSOR_MODIFIER_NONE;
+      if (gimp_image_get_floating_selection (image))
+        modifier = GIMP_CURSOR_MODIFIER_BAD;
+      else if (layer && layer != gimp_image_get_active_layer (image))
+        modifier = GIMP_CURSOR_MODIFIER_SELECT;
+
+      gimp_tool_control_set_tool_cursor (tool->control, GIMP_TOOL_CURSOR_HAND);
+      gimp_tool_control_set_cursor_modifier (tool->control, modifier);
+    }
+  else if (! gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)))
     {
       GimpImage    *image    = gimp_display_get_image (display);
       GimpDrawable *drawable = gimp_image_get_active_drawable (image);
@@ -519,6 +561,8 @@ gimp_paint_tool_cursor_update (GimpTool         *tool,
   /*  reset old stuff here so we are not interfering with the modifiers
    *  set by our subclasses
    */
+  gimp_tool_control_set_tool_cursor            (tool->control,
+                                                old_tool_cursor);
   gimp_tool_control_set_cursor_modifier        (tool->control,
                                                 old_modifier);
   gimp_tool_control_set_toggle_cursor_modifier (tool->control,
@@ -540,7 +584,8 @@ gimp_paint_tool_oper_update (GimpTool         *tool,
   GimpImage        *image         = gimp_display_get_image (display);
   GimpDrawable     *drawable      = gimp_image_get_active_drawable (image);
 
-  if (gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)))
+  if (gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (tool)) ||
+      paint_tool->picking_layer)
     {
       GIMP_TOOL_CLASS (parent_class)->oper_update (tool, coords, state,
                                                    proximity, display);
@@ -657,9 +702,11 @@ gimp_paint_tool_oper_update (GimpTool         *tool,
 static void
 gimp_paint_tool_draw (GimpDrawTool *draw_tool)
 {
-  if (! gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (draw_tool)))
+  GimpPaintTool *paint_tool = GIMP_PAINT_TOOL (draw_tool);
+
+  if (! gimp_color_tool_is_enabled (GIMP_COLOR_TOOL (draw_tool)) &&
+      ! paint_tool->picking_layer)
     {
-      GimpPaintTool  *paint_tool = GIMP_PAINT_TOOL (draw_tool);
       GimpPaintCore  *core       = paint_tool->core;
       GimpImage      *image      = gimp_display_get_image (draw_tool->display);
       GimpDrawable   *drawable   = gimp_image_get_active_drawable (image);
diff --git a/app/tools/gimppainttool.h b/app/tools/gimppainttool.h
index 387239e7f4..690dc3ee61 100644
--- a/app/tools/gimppainttool.h
+++ b/app/tools/gimppainttool.h
@@ -44,6 +44,8 @@ struct _GimpPaintTool
   gboolean       pick_colors;  /*  pick color if ctrl is pressed   */
   gboolean       draw_line;
 
+  gboolean       picking_layer; /*  pick layer in progress (alt pressed)  */
+
   gboolean       show_cursor;
   gboolean       draw_brush;
   gboolean       draw_fallback;