[gegl] buffer: in GeglBufferIterator, avoid fetching/copying whole write-only tiles

[Ell <ell src gnome org>]

commit 926e0c6c09ef5b77aabcddd3db1322b23099e617
Author: Ell <ell_se yahoo com>
Date:   Tue Jan 1 14:39:47 2019 -0500

    buffer: in GeglBufferIterator, avoid fetching/copying whole write-only tiles
    
    In GeglBufferIterator, use gegl_tile_handler_get_tile() to fetch
    tiles, instead of gegl_buffer_get_tile(), and don't preserve tile
    data when the buffer is accessed for writing only, and the entire
    tile is being written to.  This avoids unnecessarily fetching the
    tile from storage, or copying its data during uncloning.

 gegl/buffer/gegl-buffer-iterator.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)
---
diff --git a/gegl/buffer/gegl-buffer-iterator.c b/gegl/buffer/gegl-buffer-iterator.c
index 057877382..a07586c30 100644
--- a/gegl/buffer/gegl-buffer-iterator.c
+++ b/gegl/buffer/gegl-buffer-iterator.c
@@ -31,6 +31,7 @@
 #include "gegl-buffer-iterator.h"
 #include "gegl-buffer-iterator-private.h"
 #include "gegl-buffer-private.h"
+#include "gegl-tile-storage.h"
 
 typedef enum {
   GeglIteratorState_Start,
@@ -361,18 +362,26 @@ get_tile (GeglBufferIterator *iter,
       int tile_x = gegl_tile_indice (iter->items[index].roi.x + shift_x, tile_width);
       int tile_y = gegl_tile_indice (iter->items[index].roi.y + shift_y, tile_height);
 
-      sub->current_tile = gegl_buffer_get_tile (buf, tile_x, tile_y, sub->level);
+      sub->real_roi.x = (tile_x * tile_width)  - shift_x;
+      sub->real_roi.y = (tile_y * tile_height) - shift_y;
+      sub->real_roi.width  = tile_width;
+      sub->real_roi.height = tile_height;
+
+      g_rec_mutex_lock (&buf->tile_storage->mutex);
+
+      sub->current_tile = gegl_tile_handler_get_tile (
+        (GeglTileHandler *) buf,
+        tile_x, tile_y, sub->level,
+        (sub->access_mode & GEGL_ACCESS_READWRITE) != GEGL_ACCESS_WRITE ||
+        ! gegl_rectangle_contains (&sub->full_rect, &sub->real_roi));
+
+      g_rec_mutex_unlock (&buf->tile_storage->mutex);
 
       if (sub->access_mode & GEGL_ACCESS_WRITE)
         gegl_tile_lock (sub->current_tile);
       else
         gegl_tile_read_lock (sub->current_tile);
 
-      sub->real_roi.x = (tile_x * tile_width)  - shift_x;
-      sub->real_roi.y = (tile_y * tile_height) - shift_y;
-      sub->real_roi.width  = tile_width;
-      sub->real_roi.height = tile_height;
-
       sub->current_tile_mode = GeglIteratorTileMode_DirectTile;
     }
 
@@ -509,7 +518,16 @@ prepare_iteration (GeglBufferIterator *iter)
               (buf->extent.width  == buf->tile_width) &&
               (buf->extent.height == buf->tile_height))
             {
-              sub->linear_tile = gegl_buffer_get_tile (sub->buffer, 0, 0, 0);
+              g_rec_mutex_lock (&buf->tile_storage->mutex);
+
+              sub->linear_tile = gegl_tile_handler_get_tile (
+                (GeglTileHandler *) buf,
+                0, 0, 0,
+                (sub->access_mode & GEGL_ACCESS_READWRITE) !=
+                GEGL_ACCESS_WRITE ||
+                ! gegl_rectangle_contains (&sub->full_rect, &buf->extent));
+
+              g_rec_mutex_unlock (&buf->tile_storage->mutex);
 
               if (sub->access_mode & GEGL_ACCESS_WRITE)
                 gegl_tile_lock (sub->linear_tile);