[gimp] Bug 791512 - make the selection boundary detection the same as 2.8

[Thomas Manni <tmanni src gnome org>]

commit 27512d802b221df14b7c805e4ceccf710fcd0e4e
Author: Thomas Manni <thomas manni free fr>
Date:   Mon Dec 18 21:01:30 2017 +0100

    Bug 791512 - make the selection boundary detection the same as 2.8
    
    Replace the GIMP_BOUNDARY_HALF_WAY macro by two others : one for perceptual and
    one for linear gamma.
    
    Use the GIMP_BOUNDARY_HALF_WAY_LINEAR to compute channels and floating selection
    boundaries.

 app/core/gimpboundary.h                 |    3 ++-
 app/core/gimpchannel.c                  |    4 ++--
 app/core/gimplayer-floating-selection.c |    2 +-
 app/tools/gimpregionselecttool.c        |    2 +-
 4 files changed, 6 insertions(+), 5 deletions(-)
---
diff --git a/app/core/gimpboundary.h b/app/core/gimpboundary.h
index 29049ad..c2adc0a 100644
--- a/app/core/gimpboundary.h
+++ b/app/core/gimpboundary.h
@@ -20,7 +20,8 @@
 
 
 /* half intensity for mask */
-#define GIMP_BOUNDARY_HALF_WAY 0.5
+#define GIMP_BOUNDARY_HALF_WAY_PERCEPTUAL  0.5
+#define GIMP_BOUNDARY_HALF_WAY_LINEAR      0.214041
 
 
 typedef enum
diff --git a/app/core/gimpchannel.c b/app/core/gimpchannel.c
index 964a393..b6947b3 100644
--- a/app/core/gimpchannel.c
+++ b/app/core/gimpchannel.c
@@ -1169,7 +1169,7 @@ gimp_channel_real_boundary (GimpChannel         *channel,
                                                   babl_format ("Y float"),
                                                   GIMP_BOUNDARY_IGNORE_BOUNDS,
                                                   x1, y1, x2, y2,
-                                                  GIMP_BOUNDARY_HALF_WAY,
+                                                  GIMP_BOUNDARY_HALF_WAY_LINEAR,
                                                   &channel->num_segs_out);
           x1 = MAX (x1, x3);
           y1 = MAX (y1, y3);
@@ -1182,7 +1182,7 @@ gimp_channel_real_boundary (GimpChannel         *channel,
                                                      babl_format ("Y float"),
                                                      GIMP_BOUNDARY_WITHIN_BOUNDS,
                                                      x1, y1, x2, y2,
-                                                     GIMP_BOUNDARY_HALF_WAY,
+                                                     GIMP_BOUNDARY_HALF_WAY_LINEAR,
                                                      &channel->num_segs_in);
             }
           else
diff --git a/app/core/gimplayer-floating-selection.c b/app/core/gimplayer-floating-selection.c
index b1bac93..236356a 100644
--- a/app/core/gimplayer-floating-selection.c
+++ b/app/core/gimplayer-floating-selection.c
@@ -267,7 +267,7 @@ floating_sel_boundary (GimpLayer *layer,
                                                babl_format ("A float"),
                                                GIMP_BOUNDARY_WITHIN_BOUNDS,
                                                0, 0, width, height,
-                                               GIMP_BOUNDARY_HALF_WAY,
+                                               GIMP_BOUNDARY_HALF_WAY_LINEAR,
                                                &layer->fs.num_segs);
 
           /*  offset the segments  */
diff --git a/app/tools/gimpregionselecttool.c b/app/tools/gimpregionselecttool.c
index f1604a8..c1674b4 100644
--- a/app/tools/gimpregionselecttool.c
+++ b/app/tools/gimpregionselecttool.c
@@ -310,7 +310,7 @@ gimp_region_select_tool_draw (GimpDrawTool *draw_tool)
                                                  0, 0,
                                                  gegl_buffer_get_width  (region_sel->region_mask),
                                                  gegl_buffer_get_height (region_sel->region_mask),
-                                                 GIMP_BOUNDARY_HALF_WAY,
+                                                 GIMP_BOUNDARY_HALF_WAY_LINEAR,
                                                  &region_sel->n_segs);
 
         }