Spreadsheet: persistent column storage and data source

A `DataSource` provides columns for the spreadsheet to display.
Every column has a SpreadsheetColumnID as identifier. Columns
are not generated eagerly anymore, instead the main spreadsheet
code can request a column from a data source with an column
identifier. The column identifiers can be stored in DNA and allow us
to store persistent data per column.

On the user level the only thing that changes is that columns are
not shown in alphabetical order anymore. Instead, new columns
are always added on the left. The behavior can be changed,
however I'd prefer not to automate this too much currently. I think
we should just add operators to hide/reorder/resize columns soonish.

Differential Revision: https://developer.blender.org/D10901

1 files changed, 65 insertions, 0 deletions

diff --git a/source/blender/editors/space_spreadsheet/spreadsheet_data_source.hh b/source/blender/editors/space_spreadsheet/spreadsheet_data_source.hh
new file mode 100644
index 00000000000..e012fae0edf
--- /dev/null
+++ b/source/blender/editors/space_spreadsheet/spreadsheet_data_source.hh
@@ -0,0 +1,65 @@
+/*
+ * 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 2
+ * 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, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#pragma once
+
+#include "BLI_function_ref.hh"
+
+#include "spreadsheet_column.hh"
+#include "spreadsheet_column_values.hh"
+
+namespace blender::ed::spreadsheet {
+
+/**
+ * This class is subclassed to implement different data sources for the spreadsheet. A data source
+ * provides the information that should be displayed. It is not concerned with how data is layed
+ * out in the spreadsheet editor exactly.
+ */
+class DataSource {
+ public:
+  virtual ~DataSource();
+
+  /**
+   * Calls the callback with all the column ids that should be displayed as long as the user does
+   * not manually add or remove columns. The column id can be stack allocated. Therefore, the
+   * callback should not keep a reference to it (and copy it instead).
+   */
+  virtual void foreach_default_column_ids(FunctionRef<void(const SpreadsheetColumnID &)> fn) const
+  {
+    UNUSED_VARS(fn);
+  }
+
+  /**
+   * Returns the column values the given column id. If no data exists for this id, null is
+   * returned.
+   */
+  virtual std::unique_ptr<ColumnValues> get_column_values(
+      const SpreadsheetColumnID &column_id) const
+  {
+    UNUSED_VARS(column_id);
+    return {};
+  }
+
+  /**
+   * Returns the number of rows in columns returned by #get_column_values.
+   */
+  virtual int tot_rows() const
+  {
+    return 0;
+  }
+};
+
+}  // namespace blender::ed::spreadsheet