Image Engine: Store image usage to identity changes.

Previous implementation had a copy of the image user, which doesn't
contain all the data to identify changes. This patch introduces a new
struct to store the data and can be extended with other data as well
(color spaces, alpha settings).

source/blender/draw/engines/image/image_drawing_mode.hh

@@ -475,7 +475,7 @@ template<typename TextureMethod> class ScreenSpaceDrawingMode : public AbstractD
     method.update_screen_uv_bounds();
 
     /* Check for changes in the image user compared to the last time. */
-    instance_data->update_image_user(iuser);
+    instance_data->update_image_usage(iuser);
 
     /* Step: Update the GPU textures based on the changes in the image. */
     instance_data->update_gpu_texture_allocations();

source/blender/draw/engines/image/image_instance_data.hh

@@ -27,6 +27,7 @@
 #include "image_private.hh"
 #include "image_shader_params.hh"
 #include "image_texture_info.hh"
+#include "image_usage.hh"
 #include "image_wrappers.hh"
 
 #include "DRW_render.h"
@@ -40,8 +41,8 @@ constexpr int SCREEN_SPACE_DRAWING_MODE_TEXTURE_LEN = 1;
 
 struct IMAGE_InstanceData {
   struct Image *image;
-  /** Copy of the last image user to detect iuser differences that require a full update. */
-  struct ImageUser last_image_user;
+  /** Usage data of the previous time, to identify changes that require a full update. */
+  ImageUsage last_usage;
 
   PartialImageUpdater partial_update;
 
@@ -110,23 +111,11 @@ struct IMAGE_InstanceData {
     }
   }
 
-  void update_image_user(const ImageUser *image_user)
+  void update_image_usage(const ImageUser *image_user)
   {
-    short requested_pass = image_user ? image_user->pass : 0;
-    short requested_layer = image_user ? image_user->layer : 0;
-    short requested_view = image_user ? image_user->multi_index : 0;
-    /* There is room for 2 multiview textures. When a higher number is requested we should always
-     * target the first view slot. This is fine as multi view images aren't used together. */
-    if (requested_view > 1) {
-      requested_view = 0;
-    }
-
-    if (last_image_user.pass != requested_pass || last_image_user.layer != requested_layer ||
-        last_image_user.multi_index != requested_view) {
-
-      last_image_user.pass = requested_pass;
-      last_image_user.layer = requested_layer;
-      last_image_user.multi_index = requested_view;
+    ImageUsage usage(image_user);
+    if (last_usage != usage) {
+      last_usage = usage;
       reset_dirty_flag(true);
     }
   }

source/blender/draw/engines/image/image_usage.hh

@@ -0,0 +1,53 @@
+/*
+ * 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 2022, Blender Foundation.
+ */
+
+/** \file
+ * \ingroup draw_engine
+ */
+
+#pragma once
+
+/**
+ * ImageUsage contains data of the image and image user to identify changes that require a rebuild
+ * of the texture slots.
+ */
+struct ImageUsage {
+  /** Render pass of the image that is used. */
+  short pass = 0;
+  /** Layer of the image that is used.*/
+  short layer = 0;
+  /** View of the image that is used. */
+  short view = 0;
+
+  ImageUsage() = default;
+  ImageUsage(const struct ImageUser *image_user)
+  {
+    pass = image_user ? image_user->pass : 0;
+    layer = image_user ? image_user->layer : 0;
+    view = image_user ? image_user->multi_index : 0;
+  }
+
+  bool operator==(const ImageUsage &other) const
+  {
+    return memcmp(this, &other, sizeof(ImageUsage)) == 0;
+  }
+  bool operator!=(const ImageUsage &other) const
+  {
+    return !(*this == other);
+  }
+};