app: in xcf-load, avoid writing buffer data for empty tiles

When loading tile data, avoid copying the data into the GEGL
buffer when the tile is empty (i.e., all its bytes are 0), so that
GEGL doesn't allocate memory for it unnecessarily.

app/xcf/Makefile.am

@@ -25,5 +25,7 @@ libappxcf_a_SOURCES = \
 	xcf-save.h	\
 	xcf-seek.c	\
 	xcf-seek.h	\
+	xcf-utils.c	\
+	xcf-utils.h	\
 	xcf-write.c	\
 	xcf-write.h

app/xcf/xcf-load.c

@@ -70,6 +70,7 @@
 #include "xcf-load.h"
 #include "xcf-read.h"
 #include "xcf-seek.h"
+#include "xcf-utils.h"
 
 #include "gimp-log.h"
 #include "gimp-intl.h"
@@ -2064,8 +2065,11 @@ xcf_load_tile (XcfInfo       *info,
                           tile_size / bpp * n_components);
     }
 
+  if (! xcf_data_is_zero (tile_data, tile_size))
+    {
       gegl_buffer_set (buffer, tile_rect, 0, format, tile_data,
                        GEGL_AUTO_ROWSTRIDE);
+    }
 
   return TRUE;
 }
@@ -2080,6 +2084,7 @@ xcf_load_tile_rle (XcfInfo       *info,
   gint    bpp       = babl_format_get_bytes_per_pixel (format);
   gint    tile_size = bpp * tile_rect->width * tile_rect->height;
   guchar *tile_data = g_alloca (tile_size);
+  guchar  nonzero   = FALSE;
   gsize   bytes_read;
   gint    i;
   guchar *xcfdata;
@@ -2158,6 +2163,7 @@ xcf_load_tile_rle (XcfInfo       *info,
               while (length-- > 0)
                 {
                   *data = *xcfdata++;
+                  nonzero |= *data;
                   data += bpp;
                 }
             }
@@ -2189,6 +2195,7 @@ xcf_load_tile_rle (XcfInfo       *info,
                 }
 
               val = *xcfdata++;
+              nonzero |= val;
 
               for (j = 0; j < length; j++)
                 {
@@ -2199,6 +2206,8 @@ xcf_load_tile_rle (XcfInfo       *info,
         }
     }
 
+  if (nonzero)
+    {
       if (info->file_version >= 12)
         {
           gint n_components = babl_format_get_n_components (format);
@@ -2209,6 +2218,7 @@ xcf_load_tile_rle (XcfInfo       *info,
 
       gegl_buffer_set (buffer, tile_rect, 0, format, tile_data,
                        GEGL_AUTO_ROWSTRIDE);
+    }
 
   return TRUE;
 
@@ -2297,6 +2307,8 @@ xcf_load_tile_zlib (XcfInfo       *info,
         }
     }
 
+  if (! xcf_data_is_zero (tile_data, tile_size))
+    {
       if (info->file_version >= 12)
         {
           gint n_components = babl_format_get_n_components (format);
@@ -2307,6 +2319,7 @@ xcf_load_tile_zlib (XcfInfo       *info,
 
       gegl_buffer_set (buffer, tile_rect, 0, format, tile_data,
                        GEGL_AUTO_ROWSTRIDE);
+    }
 
   inflateEnd (&strm);
 

app/xcf/xcf-utils.c

@@ -0,0 +1,53 @@
+/* GIMP - The GNU Image Manipulation Program
+ * Copyright (C) 1995 Spencer Kimball and Peter Mattis
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <cairo.h>
+#include <gegl.h>
+#include <gdk-pixbuf/gdk-pixbuf.h>
+
+#include "xcf-utils.h"
+
+
+gboolean
+xcf_data_is_zero (const void *data,
+                  gint        size)
+{
+  const guint8  *data8;
+  const guint64 *data64;
+
+  for (data8 = data; size > 0 && (guintptr) data8 % 8 != 0; data8++, size--)
+    {
+      if (*data8)
+        return FALSE;
+    }
+
+  for (data64 = (gpointer) data8; size >= 8; data64++, size -= 8)
+    {
+      if (*data64)
+        return FALSE;
+    }
+
+  for (data8 = (gpointer) data64; size > 0; data8++, size--)
+    {
+      if (*data8)
+        return FALSE;
+    }
+
+  return TRUE;
+}

app/xcf/xcf-utils.h

@@ -0,0 +1,26 @@
+/* GIMP - The GNU Image Manipulation Program
+ * Copyright (C) 1995 Spencer Kimball and Peter Mattis
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __XCF_UTILS_H__
+#define __XCF_UTILS_H__
+
+
+gboolean   xcf_data_is_zero (const void *data,
+                             gint        size);
+
+
+#endif  /* __XCF_UTILS_H__ */