Commit d0468ee7 authored by Federico Mena Quintero's avatar Federico Mena Quintero Committed by Benjamin Otte

Big comment on how GtkFileSystemModel works

Let's have some documentation on the idea behind this beast...
Signed-off-by: default avatarFederico Mena Quintero <federico@novell.com>
parent 04c78019
......@@ -33,6 +33,60 @@
#include "gtktreemodel.h"
#include "gtkalias.h"
/*** Structure: how GtkFileSystemModel works
*
* This is a custom GtkTreeModel used to hold a collection of files for GtkFileChooser. There are two use cases:
*
* 1. The model populates itself from a folder, using the GIO file enumerator API. This happens if you use
* _gtk_file_system_model_new_for_directory(). This is the normal usage for showing the contents of a folder.
*
* 2. The caller populates the model by hand, with files not necessarily in the same folder. This happens
* if you use _gtk_file_system_model_new() and then _gtk_file_system_model_add_and_query_file(). This is
* the special kind of usage for "search" and "recent-files", where the file chooser gives the model the
* files to be displayed.
*
* Each file is kept in a FileModelNode structure. Each FileModelNode holds a GFile* and other data. All the
* node structures have the same size, determined at runtime, depending on the number of columns that were passed
* to _gtk_file_system_model_new() or _gtk_file_system_model_new_for_directory() (that is, the size of a node is
* not sizeof (FileModelNode), but rather model->node_size). The last field in the FileModelNode structure,
* node->values[], is an array of GValue, used to hold the data for those columns.
*
* The model stores an array of FileModelNode structures in model->files. This is a GArray where each element is
* model->node_size bytes in size (the model computes that node size when initializing itself). There are
* convenience macros, get_node() and node_index(), to access that array based on an array index or a pointer to
* a node inside the array.
*
* The model accesses files through two of its fields:
*
* model->files - GArray of FileModelNode structures.
*
* model->file_lookup - hash table that maps a GFile* to an index inside the model->files array.
*
* The model->file_lookup hash table is populated lazily. It is both accessed and populated with the
* node_get_for_file() function. The invariant is that the files in model->files[n] for n < g_hash_table_size
* (model->file_lookup) are already added to the hash table. The hash table will get cleared when we re-sort the
* files, as the array will be in a different order and the indexes need to be rebuilt.
*
* Each FileModelNode has a node->visible field, which indicates whether the node is visible in the GtkTreeView.
* A node may be invisible if, for example, it corresponds to a hidden file and the file chooser is not showing
* hidden files.
*
* Since not all nodes in the model->files array may be visible, we need a way to map visible row indexes from
* the treeview to array indexes in our array of files.
*
* Each FileModelNode has a node->index field which is the number of visible nodes in the treeview, *before and
* including* that node. This means that node->index is 1-based, instead of 0-based --- this makes some code
* simpler, believe it or not :) This also means that when the calling GtkTreeView gives us a GtkTreePath, we
* turn the 0-based treepath into a 1-based index for our purposes.
*
* We try to compute the node->index fields lazily. For this, the model keeps a model->n_indexes_valid field
* which is the count of valid indexes starting from the beginning of the model->files array. When a node
* changes its information, or when a node gets deleted, that node and the following ones get invalidated by
* simply setting model->n_indexes_valid to the array index of the node. If the model happens to need a node's
* visible index and that node is in the model->files array after model->n_indexes_valid, then the indexes get
* re-validated up to the sought node. See node_validate_indexes() for this logic.
*/
/*** DEFINES ***/
/* priority used for all async callbacks in the main loop
......@@ -51,7 +105,9 @@ struct _FileModelNode
GFile * file; /* file represented by this node or NULL for editable */
GFileInfo * info; /* info for this file or NULL if unknown */
guint index; /* if valid, index in path - aka visible nodes before this one */
guint index; /* if valid (see model->n_valid_indexes), visible nodes before and including
* this one - see the "Structure" comment above.
*/
guint visible :1; /* if the file is currently visible */
guint frozen_add :1; /* true if the model was frozen and the entry has not been added yet */
......@@ -139,9 +195,17 @@ static void remove_file (GtkFileSystemModel *model,
/*** FileModelNode ***/
/* Get a FileModelNode structure given an index in the model->files array of nodes */
#define get_node(_model, _index) ((FileModelNode *) ((_model)->files->data + (_index) * (_model)->node_size))
/* Get an index within the model->files array of nodes, given a FileModelNode* */
#define node_index(_model, _node) (((gchar *) (_node) - (_model)->files->data) / (_model)->node_size)
/* @min_index: smallest model->array index that will be valid after this call
* @min_visible: smallest node->index that will be valid after this call
*
* Passing G_MAXUINT is fine for either/both of those arguments for "validate all nodes".
*/
static void
node_validate_indexes (GtkFileSystemModel *model, guint min_index, guint min_visible)
{
......
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