[gimp] app: take transform-grid handle size into account when readjusting

[Ell <ell src gnome org>]

commit 46e16e175c4cdc9da715ec50a8b793ea9688525d
Author: Ell <ell_se yahoo com>
Date:   Fri Mar 8 08:30:11 2019 -0500

    app: take transform-grid handle size into account when readjusting
    
    In the unified-transform, scale, and perspective tools, take the
    maximal transform-grid handle size into account when readjusting
    the transform, so that the handles themselves are fully within view
    under arbitrary rotation, rather than just the corners.

 app/display/gimptooltransformgrid.h  | 5 +++++
 app/tools/gimpperspectivetool.c      | 4 +++-
 app/tools/gimpscaletool.c            | 4 +++-
 app/tools/gimpunifiedtransformtool.c | 4 +++-
 4 files changed, 14 insertions(+), 3 deletions(-)
---
diff --git a/app/display/gimptooltransformgrid.h b/app/display/gimptooltransformgrid.h
index 7037c5a8c4..e42b9ed4ed 100644
--- a/app/display/gimptooltransformgrid.h
+++ b/app/display/gimptooltransformgrid.h
@@ -22,9 +22,14 @@
 #define __GIMP_TOOL_TRANSFORM_GRID_H__
 
 
+#include "gimpcanvashandle.h"
 #include "gimptoolwidget.h"
 
 
+#define GIMP_TOOL_TRANSFORM_GRID_MAX_HANDLE_SIZE \
+  (1.5 * GIMP_CANVAS_HANDLE_SIZE_LARGE)
+
+
 typedef enum
 {
   GIMP_TRANSFORM_HANDLE_NONE,
diff --git a/app/tools/gimpperspectivetool.c b/app/tools/gimpperspectivetool.c
index 58d0e8983e..c6f7a5d98c 100644
--- a/app/tools/gimpperspectivetool.c
+++ b/app/tools/gimpperspectivetool.c
@@ -176,7 +176,9 @@ gimp_perspective_tool_readjust (GimpTransformGridTool *tg_tool)
 
   x = shell->disp_width  / 2.0;
   y = shell->disp_height / 2.0;
-  r = MIN (x, y) / G_SQRT2;
+  r = MAX (MIN (x, y) / G_SQRT2 -
+           GIMP_TOOL_TRANSFORM_GRID_MAX_HANDLE_SIZE / 2.0,
+           GIMP_TOOL_TRANSFORM_GRID_MAX_HANDLE_SIZE / 2.0);
 
   gimp_display_shell_untransform_xy_f (shell,
                                        x - r, y - r,
diff --git a/app/tools/gimpscaletool.c b/app/tools/gimpscaletool.c
index c0486c4ee5..dacea95046 100644
--- a/app/tools/gimpscaletool.c
+++ b/app/tools/gimpscaletool.c
@@ -268,7 +268,9 @@ gimp_scale_tool_readjust (GimpTransformGridTool *tg_tool)
 
   x = shell->disp_width  / 2.0;
   y = shell->disp_height / 2.0;
-  r = MIN (x, y) / G_SQRT2;
+  r = MAX (MIN (x, y) / G_SQRT2 -
+           GIMP_TOOL_TRANSFORM_GRID_MAX_HANDLE_SIZE / 2.0,
+           GIMP_TOOL_TRANSFORM_GRID_MAX_HANDLE_SIZE / 2.0);
 
   gimp_display_shell_untransform_xy_f (shell,
                                        x, y,
diff --git a/app/tools/gimpunifiedtransformtool.c b/app/tools/gimpunifiedtransformtool.c
index ba474b50b3..9957f4ccb3 100644
--- a/app/tools/gimpunifiedtransformtool.c
+++ b/app/tools/gimpunifiedtransformtool.c
@@ -188,7 +188,9 @@ gimp_unified_transform_tool_readjust (GimpTransformGridTool *tg_tool)
 
   x = shell->disp_width  / 2.0;
   y = shell->disp_height / 2.0;
-  r = MIN (x, y) / G_SQRT2;
+  r = MAX (MIN (x, y) / G_SQRT2 -
+           GIMP_TOOL_TRANSFORM_GRID_MAX_HANDLE_SIZE / 2.0,
+           GIMP_TOOL_TRANSFORM_GRID_MAX_HANDLE_SIZE / 2.0);
 
   gimp_display_shell_untransform_xy_f (shell,
                                        x, y,