Cycles: Add sample offset option

This patch exposes the sampling offset option to Blender. It is located in the "Sampling > Advanced" panel.
For example, this can be useful to parallelize rendering and distribute different chunks of samples for each computer to render.

---

I also had to add this option to `RenderWork` and `RenderScheduler` classes so that the sample count in the status string can be calculated correctly.

Reviewed By: leesonw

Differential Revision: https://developer.blender.org/D13086

2 files changed, 4 insertions, 1 deletions

diff --git a/intern/cycles/session/session.cpp b/intern/cycles/session/session.cpp
index b228939689c..299d731d9f9 100644
--- a/intern/cycles/session/session.cpp
+++ b/intern/cycles/session/session.cpp
@@ -262,6 +262,7 @@ RenderWork Session::run_update_for_next_iteration()
   }
 
   render_scheduler_.set_num_samples(params.samples);
+  render_scheduler_.set_start_sample(params.sample_offset);
   render_scheduler_.set_time_limit(params.time_limit);
 
   while (have_tiles) {
@@ -397,7 +398,7 @@ void Session::do_delayed_reset()
 
   /* Tile and work scheduling. */
   tile_manager_.reset_scheduling(buffer_params_, get_effective_tile_size());
-  render_scheduler_.reset(buffer_params_, params.samples);
+  render_scheduler_.reset(buffer_params_, params.samples, params.sample_offset);
 
   /* Passes. */
   /* When multiple tiles are used SAMPLE_COUNT pass is used to keep track of possible partial
diff --git a/intern/cycles/session/session.h b/intern/cycles/session/session.h
index 1ec0c6e9bb1..3f73593f008 100644
--- a/intern/cycles/session/session.h
+++ b/intern/cycles/session/session.h
@@ -54,6 +54,7 @@ class SessionParams {
 
   bool experimental;
   int samples;
+  int sample_offset;
   int pixel_size;
   int threads;
 
@@ -75,6 +76,7 @@ class SessionParams {
 
     experimental = false;
     samples = 1024;
+    sample_offset = 0;
     pixel_size = 1;
     threads = 0;
     time_limit = 0.0;