[gimp/gimp-2-10] app: in GimpChunkIterator, avoid preparing rect before merging

[Ell <ell src gnome org>]

commit 522e497457d35816cb13468c5a27e81b9309d4fb
Author: Ell <ell_se yahoo com>
Date:   Sun Mar 31 04:59:23 2019 -0400

    app: in GimpChunkIterator, avoid preparing rect before merging
    
    In GimpChunkIterator, avoid preparing the current rect before
    merging it back to the iterator's region, to save some work.
    
    Additionally, strengthen the iterator's invariants and simplify
    code.
    
    (cherry picked from commit c95502266ada77d9f1ab43631581dd4c393cd3f0)

 app/core/gimpchunkiterator.c | 51 ++++++++++++++++++++++----------------------
 1 file changed, 25 insertions(+), 26 deletions(-)
---
diff --git a/app/core/gimpchunkiterator.c b/app/core/gimpchunkiterator.c
index 0dfdae4652..616bb463cc 100644
--- a/app/core/gimpchunkiterator.c
+++ b/app/core/gimpchunkiterator.c
@@ -113,39 +113,34 @@ gimp_chunk_iterator_set_current_rect (GimpChunkIterator   *iter,
   cairo_region_subtract_rectangle (iter->current_region,
                                    (const cairo_rectangle_int_t *) rect);
 
-  iter->current_rect = *rect;
+  iter->current_rect   = *rect;
 
-  iter->current_x    = rect->x;
-  iter->current_y    = rect->y;
+  iter->current_x      = rect->x;
+  iter->current_y      = rect->y;
+  iter->current_height = 0;
 }
 
 static void
 gimp_chunk_iterator_merge_current_rect (GimpChunkIterator *iter)
 {
   GeglRectangle rect;
-  gint          current_height = 0;
 
   if (gegl_rectangle_is_empty (&iter->current_rect))
     return;
 
   /* merge the remainder of the current row */
-  if (iter->current_x != iter->current_rect.x)
-    {
-      current_height = iter->current_height;
-
-      rect.x      = iter->current_x;
-      rect.y      = iter->current_y;
-      rect.width  = iter->current_rect.x + iter->current_rect.width -
-                    iter->current_x;
-      rect.height = current_height;
+  rect.x      = iter->current_x;
+  rect.y      = iter->current_y;
+  rect.width  = iter->current_rect.x + iter->current_rect.width -
+                iter->current_x;
+  rect.height = iter->current_height;
 
-      cairo_region_union_rectangle (iter->current_region,
-                                    (const cairo_rectangle_int_t *) &rect);
-    }
+  cairo_region_union_rectangle (iter->current_region,
+                                (const cairo_rectangle_int_t *) &rect);
 
   /* merge the remainder of the current rect */
   rect.x      = iter->current_rect.x;
-  rect.y      = iter->current_y + current_height;
+  rect.y      = iter->current_y + iter->current_height;
   rect.width  = iter->current_rect.width;
   rect.height = iter->current_rect.y + iter->current_rect.height - rect.y;
 
@@ -160,6 +155,7 @@ gimp_chunk_iterator_merge_current_rect (GimpChunkIterator *iter)
 
   iter->current_x           = 0;
   iter->current_y           = 0;
+  iter->current_height      = 0;
 }
 
 static void
@@ -174,18 +170,21 @@ gimp_chunk_iterator_merge (GimpChunkIterator *iter)
       cairo_region_union (iter->region, iter->priority_region);
 
       g_clear_pointer (&iter->priority_region, cairo_region_destroy);
+
+      iter->current_region = iter->region;
     }
 }
 
 static gboolean
 gimp_chunk_iterator_prepare (GimpChunkIterator *iter)
 {
-  if (iter->current_x >= iter->current_rect.x + iter->current_rect.width)
+  if (iter->current_x == iter->current_rect.x + iter->current_rect.width)
     {
-      iter->current_x  = iter->current_rect.x;
-      iter->current_y += iter->current_height;
+      iter->current_x       = iter->current_rect.x;
+      iter->current_y      += iter->current_height;
+      iter->current_height  = 0;
 
-      if (iter->current_y >= iter->current_rect.y + iter->current_rect.height)
+      if (iter->current_y == iter->current_rect.y + iter->current_rect.height)
         {
           GeglRectangle rect;
 
@@ -222,6 +221,7 @@ gimp_chunk_iterator_prepare (GimpChunkIterator *iter)
 
               iter->current_x           = 0;
               iter->current_y           = 0;
+              iter->current_height      = 0;
 
               return FALSE;
             }
@@ -358,7 +358,8 @@ gimp_chunk_iterator_new (cairo_region_t *region)
 
   iter = g_slice_new0 (GimpChunkIterator);
 
-  iter->region = region;
+  iter->region         = region;
+  iter->current_region = region;
 
   g_object_get (gegl_config (),
                 "tile-width",  &iter->tile_rect.width,
@@ -396,8 +397,7 @@ gimp_chunk_iterator_set_priority_rect (GimpChunkIterator   *iter,
     {
       iter->priority_rect = *rect;
 
-      if (gimp_chunk_iterator_prepare (iter))
-        gimp_chunk_iterator_merge (iter);
+      gimp_chunk_iterator_merge (iter);
     }
 }
 
@@ -542,8 +542,7 @@ gimp_chunk_iterator_stop (GimpChunkIterator *iter,
     }
   else
     {
-      if (gimp_chunk_iterator_prepare (iter))
-        gimp_chunk_iterator_merge (iter);
+      gimp_chunk_iterator_merge (iter);
 
       result = iter->region;
     }