tools, operation: Add support for loading PS Levels presets

Photoshop stores their Levels filter presets in an
.alv file. This patch adds support for loading these
and converting them to GIMP's Level format.

The .alv file is binary, and consists of a 2 byte version
followed by 29 groups of 2 byte values for input,
output, and gamma. We only read the first four for
now, since GIMP only supports composite and then
R, G, and B individual channels.

app/operations/gimplevelsconfig.c

@@ -992,3 +992,98 @@ gimp_levels_config_save_cruft (GimpLevelsConfig  *config,
 
   return TRUE;
 }
+
+gboolean
+gimp_levels_config_load_alv (GimpLevelsConfig  *config,
+                             GInputStream      *input,
+                             GError           **error)
+{
+  GDataInputStream *data_input;
+  guint16           version = 0;
+  gint              low_input[4];
+  gint              high_input[4];
+  gint              low_output[4];
+  gint              high_output[4];
+  gdouble           gamma[4];
+
+  g_return_val_if_fail (GIMP_IS_LEVELS_CONFIG (config), FALSE);
+  g_return_val_if_fail (G_IS_INPUT_STREAM (input), FALSE);
+  g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
+
+  data_input = g_data_input_stream_new (input);
+
+  g_data_input_stream_set_byte_order (data_input,
+                                      G_DATA_STREAM_BYTE_ORDER_BIG_ENDIAN);
+
+  version = g_data_input_stream_read_uint16 (data_input, NULL, error);
+  if (! version)
+    goto error;
+
+  /* TODO: Photoshop Level presets store 29 levels, for channels beyond
+   * RGB. When we can support those, we should update the read limit */
+  for (gint i = 0; i < 4; i++)
+    {
+      low_input[i] = g_data_input_stream_read_uint16 (data_input, NULL, error);
+      if (error && *error)
+        goto error;
+
+      high_input[i] = g_data_input_stream_read_uint16 (data_input, NULL,
+                                                       error);
+      if (error && *error)
+        goto error;
+
+      low_output[i] = g_data_input_stream_read_uint16 (data_input, NULL,
+                                                       error);
+      if (error && *error)
+        goto error;
+
+      high_output[i] = g_data_input_stream_read_uint16 (data_input, NULL,
+                                                        error);
+      if (error && *error)
+        goto error;
+
+      gamma[i] = g_data_input_stream_read_int16 (data_input, NULL, error);
+      if (error && *error)
+        goto error;
+    }
+
+  g_object_unref (data_input);
+
+  g_object_freeze_notify (G_OBJECT (config));
+
+  for (gint i = 0; i < 4; i++)
+    {
+      config->low_input[i]   = low_input[i]   / 253.0;
+      config->high_input[i]  = high_input[i]  / 255.0;
+      config->gamma[i]       = gamma[i]       / 100.0;
+      config->low_output[i]  = low_output[i]  / 255.0;
+      config->high_output[i] = high_output[i] / 255.0;
+    }
+
+  config->trc          = GIMP_TRC_NON_LINEAR;
+  config->clamp_input  = TRUE;
+  config->clamp_output = TRUE;
+
+  g_object_notify (G_OBJECT (config), "trc");
+  g_object_notify (G_OBJECT (config), "low-input");
+  g_object_notify (G_OBJECT (config), "high-input");
+  g_object_notify (G_OBJECT (config), "clamp-input");
+  g_object_notify (G_OBJECT (config), "gamma");
+  g_object_notify (G_OBJECT (config), "low-output");
+  g_object_notify (G_OBJECT (config), "high-output");
+  g_object_notify (G_OBJECT (config), "clamp-output");
+
+  g_object_thaw_notify (G_OBJECT (config));
+
+  return TRUE;
+
+  error:
+    g_object_unref (data_input);
+
+    if (error && *error)
+      g_prefix_error (error, _("parse error"));
+    else
+      g_set_error (error, GIMP_DATA_ERROR, GIMP_DATA_ERROR_READ,
+                   _("parse error"));
+  return FALSE;
+}

app/operations/gimplevelsconfig.h

@@ -89,5 +89,8 @@ gboolean   gimp_levels_config_save_cruft       (GimpLevelsConfig      *config,
                                                 GOutputStream         *output,
                                                 GError               **error);
 
+gboolean   gimp_levels_config_load_alv         (GimpLevelsConfig      *config,
+                                                GInputStream          *input,
+                                                GError               **error);
 
 #endif /* __GIMP_LEVELS_CONFIG_H__ */

app/tools/gimplevelstool.c

@@ -35,6 +35,7 @@
 #include "core/gimp-gui.h"
 #include "core/gimpasync.h"
 #include "core/gimpcancelable.h"
+#include "core/gimpdata.h"
 #include "core/gimpdrawable.h"
 #include "core/gimpdrawable-histogram.h"
 #include "core/gimperror.h"
@@ -742,7 +743,11 @@ gimp_levels_tool_settings_import (GimpFilterTool  *filter_tool,
                                  &bytes_read, NULL, error) ||
       bytes_read != sizeof (header))
     {
-      g_prefix_error (error, _("Could not read header: "));
+      if (error && *error)
+        g_prefix_error (error, _("Could not read header: "));
+      else
+        g_set_error (error, GIMP_DATA_ERROR, GIMP_DATA_ERROR_READ,
+                     _("Could not read header: "));
       return FALSE;
     }
 
@@ -751,6 +756,10 @@ gimp_levels_tool_settings_import (GimpFilterTool  *filter_tool,
   if (g_str_has_prefix (header, "# GIMP Levels File\n"))
     return gimp_levels_config_load_cruft (config, input, error);
 
+  /* Check if we're loading a Photoshop Levels preset .alv file */
+  if (bytes_read > 2 && header[0] == 0 && (header[1] == 2))
+    return gimp_levels_config_load_alv (config, input, error);
+
   return GIMP_FILTER_TOOL_CLASS (parent_class)->settings_import (filter_tool,
                                                                  input,
                                                                  error);