[gimp] Issue #6435: Off canvas guides.

[Jehan <jehanp src gnome org>]

commit 015f49467dcb5b4640db1d96386e2c1cd95d8f37
Author: Jehan <jehan girinstud io>
Date:   Sat Feb 13 17:34:48 2021 +0100

    Issue #6435: Off canvas guides.
    
    Allow guides with off-canvas position since we can now view and work
    outside the canvas.
    
    The guide deletion interaction does not change too much, except you
    don't delete a guide because it's dropped off-canvas but off the display
    viewport area instead.
    
    The XCF format is technically unchanged as PROP_GUIDES was already
    expecting an int32 coordinate (with max value at GIMP_MAX_IMAGE_SIZE,
    way below uint32 max anyway). Yet our code and XCF docs was explicitly
    asking to ignore negative coordinate guides, which makes a change in
    behavior for the XCF parser, hence a new version XCF 15. Loading will
    still ignore negative position guides (even also bigger than image
    dimension guides now) for XCF 14 and below, but will now accept any
    position for XCF 15 and above.

 app/core/gimpimage-guides.c | 10 ----------
 app/core/gimpimage.c        | 27 ++++++++++++++++++++++++++-
 app/tools/gimpguidetool.c   |  4 +---
 app/xcf/xcf-load.c          | 26 ++++++++++++++++++++++----
 app/xcf/xcf.c               |  3 ++-
 devel-docs/xcf.txt          | 10 ++++++++--
 6 files changed, 59 insertions(+), 21 deletions(-)
---
diff --git a/app/core/gimpimage-guides.c b/app/core/gimpimage-guides.c
index 54f85cb120..412c142599 100644
--- a/app/core/gimpimage-guides.c
+++ b/app/core/gimpimage-guides.c
@@ -42,8 +42,6 @@ gimp_image_add_hguide (GimpImage *image,
   GimpGuide *guide;
 
   g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
-  g_return_val_if_fail (position >= 0 &&
-                        position <= gimp_image_get_height (image), NULL);
 
   guide = gimp_guide_new (GIMP_ORIENTATION_HORIZONTAL,
                           image->gimp->next_guide_id++);
@@ -66,8 +64,6 @@ gimp_image_add_vguide (GimpImage *image,
   GimpGuide *guide;
 
   g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
-  g_return_val_if_fail (position >= 0 &&
-                        position <= gimp_image_get_width (image), NULL);
 
   guide = gimp_guide_new (GIMP_ORIENTATION_VERTICAL,
                           image->gimp->next_guide_id++);
@@ -137,12 +133,6 @@ gimp_image_move_guide (GimpImage *image,
 {
   g_return_if_fail (GIMP_IS_IMAGE (image));
   g_return_if_fail (GIMP_IS_GUIDE (guide));
-  g_return_if_fail (position >= 0);
-
-  if (gimp_guide_get_orientation (guide) == GIMP_ORIENTATION_HORIZONTAL)
-    g_return_if_fail (position <= gimp_image_get_height (image));
-  else
-    g_return_if_fail (position <= gimp_image_get_width (image));
 
   if (gimp_guide_is_custom (guide))
     push_undo = FALSE;
diff --git a/app/core/gimpimage.c b/app/core/gimpimage.c
index 604cb49d25..23b22a1d8c 100644
--- a/app/core/gimpimage.c
+++ b/app/core/gimpimage.c
@@ -2821,10 +2821,30 @@ gimp_image_get_xcf_version (GimpImage    *image,
   if (g_list_length (gimp_image_get_selected_layers (image)) > 1)
     {
       ADD_REASON (g_strdup_printf (_("Multiple layer selection was "
-                                     "added in %s"), "GIMP 2.10.20"));
+                                     "added in %s"), "GIMP 3.0.0"));
       version = MAX (14, version);
     }
 
+  if ((list = gimp_image_get_guides (image)))
+    {
+      for (; list; list = g_list_next (list))
+        {
+          gint32 position = gimp_guide_get_position (list->data);
+
+          if (position < 0 ||
+              (gimp_guide_get_orientation (list->data) == GIMP_ORIENTATION_HORIZONTAL &&
+               position > gimp_image_get_height (image)) ||
+              /* vertical guide. */
+               position > gimp_image_get_width (image))
+            {
+              ADD_REASON (g_strdup_printf (_("Off-canvas guides "
+                                             "added in %s"), "GIMP 3.0.0"));
+              version = MAX (15, version);
+              break;
+            }
+        }
+    }
+
 #undef ADD_REASON
 
   switch (version)
@@ -2854,6 +2874,11 @@ gimp_image_get_xcf_version (GimpImage    *image,
       if (gimp_version)   *gimp_version   = 210;
       if (version_string) *version_string = "GIMP 2.10";
       break;
+    case 14:
+    case 15:
+      if (gimp_version)   *gimp_version   = 300;
+      if (version_string) *version_string = "GIMP 3.0";
+      break;
     }
 
   if (version_reason && reasons)
diff --git a/app/tools/gimpguidetool.c b/app/tools/gimpguidetool.c
index 55d5732155..5e1db2ee19 100644
--- a/app/tools/gimpguidetool.c
+++ b/app/tools/gimpguidetool.c
@@ -176,9 +176,7 @@ gimp_guide_tool_button_release (GimpTool              *tool,
 
           n_non_custom_guides += ! guide->custom;
 
-          if (guide->position == GIMP_GUIDE_POSITION_UNDEFINED ||
-              guide->position <  0                             ||
-              guide->position > max_position)
+          if (guide->position == GIMP_GUIDE_POSITION_UNDEFINED)
             {
               remove_guides = TRUE;
             }
diff --git a/app/xcf/xcf-load.c b/app/xcf/xcf-load.c
index 462ae8ac1e..6bf0d505ef 100644
--- a/app/xcf/xcf-load.c
+++ b/app/xcf/xcf-load.c
@@ -889,8 +889,14 @@ xcf_load_image_props (XcfInfo   *info,
                 xcf_read_int32 (info, (guint32 *) &position,    1);
                 xcf_read_int8  (info, (guint8 *)  &orientation, 1);
 
-                /*  skip -1 guides from old XCFs  */
-                if (position < 0)
+                /* Some very old XCF had -1 guides which have been
+                 * skipped since 2003 (commit 909a28ced2).
+                 * Then XCF up to version 14 only had positive guide
+                 * positions.
+                 * Since XCF 15 (GIMP 3.0), off-canvas guides became a
+                 * thing.
+                 */
+                if (info->file_version < 15 && position < 0)
                   continue;
 
                 GIMP_LOG (XCF, "prop guide orientation=%d position=%d",
@@ -899,11 +905,23 @@ xcf_load_image_props (XcfInfo   *info,
                 switch (orientation)
                   {
                   case XCF_ORIENTATION_HORIZONTAL:
-                    gimp_image_add_hguide (image, position, FALSE);
+                    if (info->file_version < 15 && position > gimp_image_get_height (image))
+                      gimp_message (info->gimp, G_OBJECT (info->progress),
+                                    GIMP_MESSAGE_WARNING,
+                                    "Ignoring off-canvas horizontal guide (position %d) in XCF %d file",
+                                    position, info->file_version);
+                    else
+                      gimp_image_add_hguide (image, position, FALSE);
                     break;
 
                   case XCF_ORIENTATION_VERTICAL:
-                    gimp_image_add_vguide (image, position, FALSE);
+                    if (info->file_version < 15 && position > gimp_image_get_width (image))
+                      gimp_message (info->gimp, G_OBJECT (info->progress),
+                                    GIMP_MESSAGE_WARNING,
+                                    "Ignoring off-canvas vertical guide (position %d) in XCF %d file",
+                                    position, info->file_version);
+                    else
+                      gimp_image_add_vguide (image, position, FALSE);
                     break;
 
                   default:
diff --git a/app/xcf/xcf.c b/app/xcf/xcf.c
index 6853573d5d..d079b0a549 100644
--- a/app/xcf/xcf.c
+++ b/app/xcf/xcf.c
@@ -82,7 +82,8 @@ static GimpXcfLoaderFunc * const xcf_loaders[] =
   xcf_load_image,   /* version 11 */
   xcf_load_image,   /* version 12 */
   xcf_load_image,   /* version 13 */
-  xcf_load_image    /* version 14 */
+  xcf_load_image,   /* version 14 */
+  xcf_load_image    /* version 15 */
 };
 
 
diff --git a/devel-docs/xcf.txt b/devel-docs/xcf.txt
index 0a64c1a944..0692b9c17e 100644
--- a/devel-docs/xcf.txt
+++ b/devel-docs/xcf.txt
@@ -176,10 +176,14 @@ other than 8-bit gamma), zlib compression and 64-bit offsets for XCF
 files bigger than 4GB.
 
 Version 14:
-Since GIMP 2.10.20, released on 2020-MM-DD.
+Since GIMP 3.0.0, released on TODO.
 Allows multiple layers to have the property PROP_ACTIVE_LAYER, hence
 multiple layers selected at once.
 
+Version 15:
+Since GIMP 3.0.0, released on TODO.
+PROP_GUIDES now allows off-canvas guide positions, i.e. negative
+positions and over canvas-dimensions positions.
 
 1. BASIC CONCEPTS
 =================
@@ -872,7 +876,9 @@ PROP_GUIDES (editing state)
   It appears if any guides have been defined.
 
   Some old XCF files define guides with negative coordinates; those
-  should be ignored by readers.
+  should be ignored by readers for XCF < 15. Since XCF 15, off-canvas
+  guides are possible, such as negative coordinates or bigger than the
+  canvas width/height.
 
 PROP_PATHS
   uint32  23       Type identification