[dia] [transform] Improve handling of pure translation and scaling

[Hans Breuer <hans src gnome org>]

commit 097b1df7fd9230789a9a8f4d58e2d1a9788166a8
Author: Hans Breuer <hans breuer org>
Date:   Fri Oct 8 20:49:05 2010 +0200

    [transform] Improve handling of pure translation and scaling
    
    Use dia_matrix_is_identity() to drop identity matrix when passed
    in to group_create_with_matrix(). The scaling in move_handle() had
    issues on rotated groups. Scaling is now relative to top-left corner,
    not only if it matches object position.

 lib/group.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)
---
diff --git a/lib/group.c b/lib/group.c
index b62ec4c..4b32994 100644
--- a/lib/group.c
+++ b/lib/group.c
@@ -206,7 +206,7 @@ group_move_handle(Group *group, Handle *handle, Point *to, ConnectionPoint *cp,
   /* only flies, when the top left handle is the position */
   gboolean also_move = (   group->resize_handles[0].pos.x == pos.x 
                         && group->resize_handles[0].pos.y == pos.y);
-  Point top_left = group->resize_handles[0].pos;
+  Point top_left = { bb->left, bb->top };
   Point delta;
   /* before and after width and height */
   real w0, h0, w1, h1;
@@ -259,8 +259,8 @@ group_move_handle(Group *group, Handle *handle, Point *to, ConnectionPoint *cp,
     group->matrix->xx = 1.0;
     group->matrix->yy = 1.0;
   }
-  group->matrix->xx *= (w1 / w0);
-  group->matrix->yy *= (h1 / h0);
+
+  cairo_matrix_scale ((cairo_matrix_t *)group->matrix, w1 / w0, h1 / h0);
 
   group_update_data(group);
 
@@ -471,6 +471,11 @@ group_create_with_matrix(GList *objects, DiaMatrix *matrix)
     matrix->x0 = matrix->y0 = 0; /* offset used internally */
     object_list_move_delta(group->objects, &delta);
   }
+  if (dia_matrix_is_identity (matrix)) {
+    /* just drop it as it has no effect */
+    g_free (matrix);
+    matrix = NULL;
+  }
   group->matrix = matrix;
   group_update_data(group);
   return &group->object;