1 files changed, 78 insertions, 0 deletions
diff --git a/source/blender/draw/engines/image/image_partial_updater.hh b/source/blender/draw/engines/image/image_partial_updater.hh
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index 00000000000..f0c1db2331a
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+++ b/source/blender/draw/engines/image/image_partial_updater.hh
@@ -0,0 +1,78 @@
+/*
+ * 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.
+ *
+ * Copyright 2021, Blender Foundation.
+ */
+
+/** \file
+ * \ingroup draw_engine
+ */
+
+#pragma once
+
+#include "BKE_image.h"
+#include "BKE_image_partial_update.hh"
+
+struct PartialImageUpdater {
+  struct PartialUpdateUser *user;
+  const struct Image *image;
+
+  /**
+   * \brief Ensure that there is a partial update user for the given image.
+   */
+  void ensure_image(const Image *image)
+  {
+    if (!is_valid(image)) {
+      free();
+      create(image);
+    }
+  }
+
+  virtual ~PartialImageUpdater()
+  {
+    free();
+  }
+
+ private:
+  /**
+   * \brief check if the partial update user can still be used for the given image.
+   *
+   * When switching to a different image the partial update user should be recreated.
+   */
+  bool is_valid(const Image *new_image) const
+  {
+    if (image != new_image) {
+      return false;
+    }
+
+    return user != nullptr;
+  }
+
+  void create(const Image *image)
+  {
+    BLI_assert(user == nullptr);
+    user = BKE_image_partial_update_create(image);
+    image = image;
+  }
+
+  void free()
+  {
+    if (user != nullptr) {
+      BKE_image_partial_update_free(user);
+      user = nullptr;
+      image = nullptr;
+    }
+  }
+};