Render: faster animation and re-rendering with Persistent Data

For Cycles, when enabling the Persistent Data option, the full render data
will be preserved from frame-to-frame in animation renders and between
re-renders of the scene. This means that any modifier evaluation, BVH
building, OpenGL vertex buffer uploads, etc, can be done only once for
unchanged objects. This comes at an increased memory cost.

Previously there option was named Persistent Images and had a more limited
impact on render time and memory.

When using multiple view layers, only data from a single view layer is
preserved to keep memory usage somewhat under control. However objects
shared between view layers are preserved, and so this can speedup such
renders as well, even single frame renders.

For Eevee and Workbench this option is not available, however these engines
will now always reuse the depsgraph for animation and multiple view layers.
This can significantly speed up rendering.

These engines do not support sharing the depsgraph between re-renders, due
to technical issues regarding OpenGL contexts. Support for this could be added
if those are solved, see the code comments for details.

1 files changed, 10 insertions, 26 deletions

diff --git a/intern/cycles/blender/blender_session.cpp b/intern/cycles/blender/blender_session.cpp
index ae13310789e..bf4d80ce51b 100644
--- a/intern/cycles/blender/blender_session.cpp
+++ b/intern/cycles/blender/blender_session.cpp
@@ -143,12 +143,6 @@ void BlenderSession::create_session()
 
   session->scene = scene;
 
-  /* There is no single depsgraph to use for the entire render.
-   * So we need to handle this differently.
-   *
-   * We could loop over the final render result render layers in pipeline and keep Cycles unaware
-   * of multiple layers, or perhaps move syncing further down in the pipeline.
-   */
   /* create sync */
   sync = new BlenderSync(b_engine, b_data, b_scene, scene, !background, session->progress);
   BL::Object b_camera_override(b_engine.camera_override());
@@ -213,7 +207,7 @@ void BlenderSession::reset_session(BL::BlendData &b_data, BL::Depsgraph &b_depsg
   SceneParams scene_params = BlenderSync::get_scene_params(b_scene, background);
 
   if (scene->params.modified(scene_params) || session->params.modified(session_params) ||
-      !scene_params.persistent_data) {
+      !this->b_render.use_persistent_data()) {
     /* if scene or session parameters changed, it's easier to simply re-create
      * them rather than trying to distinguish which settings need to be updated
      */
@@ -225,7 +219,6 @@ void BlenderSession::reset_session(BL::BlendData &b_data, BL::Depsgraph &b_depsg
   }
 
   session->progress.reset();
-  scene->reset();
 
   session->tile_manager.set_tile_order(session_params.tile_order);
 
@@ -234,12 +227,15 @@ void BlenderSession::reset_session(BL::BlendData &b_data, BL::Depsgraph &b_depsg
    */
   session->stats.mem_peak = session->stats.mem_used;
 
-  /* There is no single depsgraph to use for the entire render.
-   * See note on create_session().
-   */
-  /* sync object should be re-created */
-  delete sync;
-  sync = new BlenderSync(b_engine, b_data, b_scene, scene, !background, session->progress);
+  if (is_new_session) {
+    /* Sync object should be re-created for new scene. */
+    delete sync;
+    sync = new BlenderSync(b_engine, b_data, b_scene, scene, !background, session->progress);
+  }
+  else {
+    /* Sync recalculations to do just the required updates. */
+    sync->sync_recalc(b_depsgraph, b_v3d);
+  }
 
   BL::SpaceView3D b_null_space_view3d(PointerRNA_NULL);
   BL::RegionView3D b_null_region_view3d(PointerRNA_NULL);
@@ -598,18 +594,6 @@ void BlenderSession::render(BL::Depsgraph &b_depsgraph_)
   /* clear callback */
   session->write_render_tile_cb = function_null;
   session->update_render_tile_cb = function_null;
-
-  /* TODO: find a way to clear this data for persistent data render */
-#if 0
-  /* free all memory used (host and device), so we wouldn't leave render
-   * engine with extra memory allocated
-   */
-
-  session->device_free();
-
-  delete sync;
-  sync = NULL;
-#endif
 }
 
 static int bake_pass_filter_get(const int pass_filter)