[dia] transform: Fix Group::move_handle() to only move the desired handles

[Hans Breuer <hans src gnome org>]

commit beb381aee1803b3864d7dcef75891655caaacc1d
Author: Hans Breuer <hans breuer org>
Date:   Fri Sep 26 19:25:03 2014 +0200

    transform: Fix Group::move_handle() to only move the desired handles
    
    DiaObject::move_handle() method has some constraints, i.e it must be
    reversible by moving back exactly that handle to the previous position.
    To accomplish this restrict the minimum size of the transformed group
    and calculate a matrix to keep the opposite handle position fixed.
    
    Also rename array Group::resize_handles to just Group::handles.

 lib/group.c |  125 ++++++++++++++++++++++++++++++----------------------------
 1 files changed, 65 insertions(+), 60 deletions(-)
---
diff --git a/lib/group.c b/lib/group.c
index d3185c6..86d8e49 100644
--- a/lib/group.c
+++ b/lib/group.c
@@ -33,7 +33,7 @@ struct _Group {
   /*! \protected DiaObject must be first because this is a 'subclass' of it. */
   DiaObject object;
   /*! \protected To move handles use Group::move_handle() */
-  Handle resize_handles[8];
+  Handle handles[8];
   /*! \protected To group objects use group_create() */
   GList *objects;
   /*! \protected Description of the contained properties */
@@ -135,37 +135,37 @@ group_update_handles(Group *group)
 {
   Rectangle *bb = &group->object.bounding_box;
   
-  group->resize_handles[0].id = HANDLE_RESIZE_NW;
-  group->resize_handles[0].pos.x = bb->left;
-  group->resize_handles[0].pos.y = bb->top;
+  group->handles[0].id = HANDLE_RESIZE_NW;
+  group->handles[0].pos.x = bb->left;
+  group->handles[0].pos.y = bb->top;
 
-  group->resize_handles[1].id = HANDLE_RESIZE_N;
-  group->resize_handles[1].pos.x = (bb->left + bb->right) / 2.0;
-  group->resize_handles[1].pos.y = bb->top;
+  group->handles[1].id = HANDLE_RESIZE_N;
+  group->handles[1].pos.x = (bb->left + bb->right) / 2.0;
+  group->handles[1].pos.y = bb->top;
 
-  group->resize_handles[2].id = HANDLE_RESIZE_NE;
-  group->resize_handles[2].pos.x = bb->right;
-  group->resize_handles[2].pos.y = bb->top;
+  group->handles[2].id = HANDLE_RESIZE_NE;
+  group->handles[2].pos.x = bb->right;
+  group->handles[2].pos.y = bb->top;
 
-  group->resize_handles[3].id = HANDLE_RESIZE_W;
-  group->resize_handles[3].pos.x = bb->left;
-  group->resize_handles[3].pos.y = (bb->top + bb->bottom) / 2.0;
+  group->handles[3].id = HANDLE_RESIZE_W;
+  group->handles[3].pos.x = bb->left;
+  group->handles[3].pos.y = (bb->top + bb->bottom) / 2.0;
 
-  group->resize_handles[4].id = HANDLE_RESIZE_E;
-  group->resize_handles[4].pos.x = bb->right;
-  group->resize_handles[4].pos.y = (bb->top + bb->bottom) / 2.0;
+  group->handles[4].id = HANDLE_RESIZE_E;
+  group->handles[4].pos.x = bb->right;
+  group->handles[4].pos.y = (bb->top + bb->bottom) / 2.0;
 
-  group->resize_handles[5].id = HANDLE_RESIZE_SW;
-  group->resize_handles[5].pos.x = bb->left;
-  group->resize_handles[5].pos.y = bb->bottom;
+  group->handles[5].id = HANDLE_RESIZE_SW;
+  group->handles[5].pos.x = bb->left;
+  group->handles[5].pos.y = bb->bottom;
 
-  group->resize_handles[6].id = HANDLE_RESIZE_S;
-  group->resize_handles[6].pos.x = (bb->left + bb->right) / 2.0;
-  group->resize_handles[6].pos.y = bb->bottom;
+  group->handles[6].id = HANDLE_RESIZE_S;
+  group->handles[6].pos.x = (bb->left + bb->right) / 2.0;
+  group->handles[6].pos.y = bb->bottom;
 
-  group->resize_handles[7].id = HANDLE_RESIZE_SE;
-  group->resize_handles[7].pos.x = bb->right;
-  group->resize_handles[7].pos.y = bb->bottom;
+  group->handles[7].id = HANDLE_RESIZE_SE;
+  group->handles[7].pos.x = bb->right;
+  group->handles[7].pos.y = bb->bottom;
 }
 
 /*! \brief Update connection points positions of contained objects
@@ -218,9 +218,9 @@ group_move_handle(Group *group, Handle *handle, Point *to, ConnectionPoint *cp,
   Rectangle *bb = &obj->bounding_box;
   /* top and left handles are also changing the objects position */
   Point top_left = { bb->left, bb->top };
-  Point delta = { 0.0, 0.0 };
   /* before and after width and height */
   real w0, h0, w1, h1;
+  Point fixed;
   
   assert(handle->id>=HANDLE_RESIZE_NW);
   assert(handle->id<=HANDLE_RESIZE_SE);
@@ -234,41 +234,51 @@ group_move_handle(Group *group, Handle *handle, Point *to, ConnectionPoint *cp,
    */
   switch(handle->id) {
   case HANDLE_RESIZE_NW:
-    delta.x = to->x - top_left.x;
-    delta.y = to->y - top_left.y;
-    w1 = w0 - delta.x;
-    h1 = h0 - delta.y;
+    g_assert(group->handles[7].id == HANDLE_RESIZE_SE);
+    fixed = group->handles[7].pos;
+    w1 = w0 - (to->x - top_left.x);
+    h1 = h0 - (to->y - top_left.y);
     break;
   case HANDLE_RESIZE_N:
-    delta.y = to->y - top_left.y;
-    h1 = h0 - delta.y;
+    g_assert(group->handles[6].id == HANDLE_RESIZE_S);
+    fixed = group->handles[6].pos;
+    h1 = h0 - (to->y - top_left.y);
     break;
   case HANDLE_RESIZE_NE:
-    delta.y = to->y - top_left.y;
+    g_assert(group->handles[5].id == HANDLE_RESIZE_SW);
+    fixed = group->handles[5].pos;
     w1 = to->x - top_left.x;
-    h1 = h0 - delta.y;
+    h1 = h0 - (to->y - top_left.y);
     break;
   case HANDLE_RESIZE_W:
-    delta.x = to->x - top_left.x;
-    w1 = w0 - delta.x;
+    g_assert(group->handles[4].id == HANDLE_RESIZE_E);
+    fixed = group->handles[4].pos;
+    w1 = w0 - (to->x - top_left.x);
     break;
   case HANDLE_RESIZE_E:
+    g_assert(group->handles[3].id == HANDLE_RESIZE_W);
+    fixed = group->handles[3].pos;
     w1 = to->x - top_left.x;
     break;
   case HANDLE_RESIZE_SW:
-    delta.x = to->x - top_left.x;
-    w1 = w0 - delta.x;
+    g_assert(group->handles[2].id == HANDLE_RESIZE_NE);
+    fixed = group->handles[2].pos;
+    w1 = w0 - (to->x - top_left.x);
     h1 = to->y - top_left.y;
     break;
-  case HANDLE_RESIZE_SE:
-    w1 = to->x - top_left.x;
+  case HANDLE_RESIZE_S:
+    g_assert(group->handles[1].id == HANDLE_RESIZE_N);
+    fixed = group->handles[1].pos;
     h1 = to->y - top_left.y;
     break;
-  case HANDLE_RESIZE_S:
+  case HANDLE_RESIZE_SE:
+    g_assert(group->handles[0].id == HANDLE_RESIZE_NW);
+    fixed = group->handles[0].pos;
+    w1 = to->x - top_left.x;
     h1 = to->y - top_left.y;
     break;
   default:
-    g_warning("group_move_handle() called with wrong handle-id\n");
+    g_warning("group_move_handle() called with wrong handle-id %d", handle->id);
   }
 
   if (!group->matrix) {
@@ -281,22 +291,17 @@ group_move_handle(Group *group, Handle *handle, Point *to, ConnectionPoint *cp,
    * it to respective object offset. BEWARE: this is not completely
    * reversible, so we might need to deliver some extra undo information.
    */
+  w1 = MAX(w1, 0.05); /* arbitrary minimum size */
+  h1 = MAX(h1, 0.05);
   {
-    DiaMatrix mat;
-
-    delta.x += group->matrix->x0;
-    delta.y += group->matrix->y0;
-    group->matrix->x0 = group->matrix->y0 = 0.0;
-    /* it's just another matrix transform */
-    mat.xx = w1/w0;
-    mat.yy = h1/h0;
-    /* no rotation via handles */
-    mat.yx = mat.xy = 0.0;
-    
-    dia_matrix_multiply (group->matrix, group->matrix, &mat);
-    /* restore complete offset */
-    group->matrix->x0 = delta.x;
-    group->matrix->y0 = delta.y;
+    DiaMatrix m = {w1/w0, 0, 0, h1/h0, 0, 0 };
+    DiaMatrix t = { 1, 0, 0, 1, fixed.x, fixed.y };
+
+    dia_matrix_multiply (&m, &m, &t);
+    t.x0 = -fixed.x;
+    t.y0 = -fixed.y;
+    dia_matrix_multiply (&m, &t, &m);
+    dia_matrix_multiply (group->matrix, group->matrix, &m);
   }
   group_update_data(group);
 
@@ -408,8 +413,8 @@ group_copy(Group *group)
   object_copy(obj, newobj);
   
   for (i=0;i<8;i++) {
-    newobj->handles[i] = &newgroup->resize_handles[i];
-    newgroup->resize_handles[i] = group->resize_handles[i];
+    newobj->handles[i] = &newgroup->handles[i];
+    newgroup->handles[i] = group->handles[i];
   }
   
   newgroup->matrix = g_memdup(group->matrix, sizeof(DiaMatrix));
@@ -571,7 +576,7 @@ group_create(GList *objects)
   }
 
   for (i=0;i<8;i++) {
-    obj->handles[i] = &group->resize_handles[i];
+    obj->handles[i] = &group->handles[i];
     obj->handles[i]->type = HANDLE_MAJOR_CONTROL;
     obj->handles[i]->connect_type = HANDLE_NONCONNECTABLE;
     obj->handles[i]->connected_to = NULL;