DrawManager: Image engine support huge images.

Adding better support for drawing huge images in the image/uv editor. Also solved tearing artifacts.
The approach is that for each image/uv editor a screen space gpu texture is created that only contains
the visible pixels. When zooming or panning the gpu texture is rebuild.

Although the solution isn't memory intensive other parts of blender memory usage scales together with
the image size.

* Due to complexity we didn't implement partial updates when drawing images tiled (wrap repeat).
  This could be added, but is complicated as a change in the source could mean many different
  changes on the GPU texture. The work around for now is to tag all gpu textures to be dirty when
  changes are detected.

Original plan was to have 4 screen space images to support panning without gpu texture creation.
For now we don't see the need to implement it as the solution is already fast. Especially when
GPU memory is shared with CPU ram.

Reviewed By: fclem

Maniphest Tasks: T92525, T92903

Differential Revision: https://developer.blender.org/D13424

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
new file mode 100644
index 00000000000..f0c1db2331a
--- /dev/null
+++ 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;
+    }
+  }
+};