1 files changed, 106 insertions, 0 deletions
diff --git a/src/ui/widget/canvas/stores.h b/src/ui/widget/canvas/stores.h
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+++ b/src/ui/widget/canvas/stores.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Abstraction of the store/snapshot mechanism.
+ * Copyright (C) 2022 PBS <pbs3141@gmail.com>
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+#ifndef INKSCAPE_UI_WIDGET_CANVAS_STORES_H
+#define INKSCAPE_UI_WIDGET_CANVAS_STORES_H
+
+#include "fragment.h"
+#include "util.h"
+
+namespace Inkscape {
+namespace UI {
+namespace Widget {
+struct Fragment;
+class Prefs;
+class Graphics;
+
+class Stores
+{
+public:
+    enum class Mode
+    {
+        None,     /// Not initialised or just reset; no stores exist yet.
+        Normal,   /// Normal mode consisting of just a backing store.
+        Decoupled /// Decoupled mode consisting of both a backing store and a snapshot store.
+    };
+
+    enum class Action
+    {
+        None,      /// The backing store was not changed.
+        Recreated, /// The backing store was completely recreated.
+        Shifted    /// The backing store was shifted into a new rectangle.
+    };
+    
+    struct Store : Fragment
+    {
+        /**
+         * The region of space containing drawn content.
+         * For the snapshot, this region is transformed to store space and approximated inwards.
+         */
+        Cairo::RefPtr<Cairo::Region> drawn;
+    };
+
+    /// Construct a blank object with no stores.
+    Stores(Prefs const &prefs)
+        : _mode(Mode::None)
+        , _graphics(nullptr)
+        , _prefs(prefs) {}
+
+    /// Set the pointer to the graphics object.
+    void set_graphics(Graphics *g) { _graphics = g; }
+
+    /// Discards all stores. (The actual operation on the graphics is performed on the next update().)
+    void reset();
+
+    /// Respond to a viewport change. (Requires a valid graphics.)
+    Action update(Fragment const &view);
+
+    /// Respond to drawing of the backing store having finished. (Requires a valid graphics.)
+    Action finished_draw(Fragment const &view);
+
+    /// Record a rectangle as being drawn to the store.
+    void mark_drawn(Geom::IntRect const &rect) { _store.drawn->do_union(geom_to_cairo(rect)); }
+
+    // Getters.
+    Store const &store() const { return _store; }
+    Store const &snapshot() const { return _snapshot; }
+    Mode mode() const { return _mode; }
+
+private:
+    // Internal state.
+    Mode _mode;
+    Store _store, _snapshot;
+
+    // The graphics object that executes the operations on the stores.
+    Graphics *_graphics;
+
+    // The preferences object we read preferences from.
+    Prefs const &_prefs;
+
+    // Internal actions.
+    Geom::IntRect centered(Fragment const &view) const;
+    void recreate_store(Fragment const &view);
+    void shift_store(Fragment const &view);
+    void take_snapshot(Fragment const &view);
+    void snapshot_combine(Fragment const &view);
+};
+
+} // namespace Widget
+} // namespace UI
+} // namespace Inkscape
+
+#endif // INKSCAPE_UI_WIDGET_CANVAS_STORES_H
+
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4 :