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

3 files changed, 19 insertions, 2 deletions

diff --git a/intern/cycles/blender/addon/properties.py b/intern/cycles/blender/addon/properties.py
index 64613216be0..986d5d972c1 100644
--- a/intern/cycles/blender/addon/properties.py
+++ b/intern/cycles/blender/addon/properties.py
@@ -325,6 +325,13 @@ class CyclesRenderSettings(bpy.types.PropertyGroup):
         default=1024,
     )
 
+    sample_offset: IntProperty(
+        name="Sample Offset",
+        description="Number of samples to skip when starting render",
+        min=0, max=(1 << 24),
+        default=0,
+    )
+
     time_limit: FloatProperty(
         name="Time Limit",
         description="Limit the render time (excluding synchronization time)."
diff --git a/intern/cycles/blender/addon/ui.py b/intern/cycles/blender/addon/ui.py
index 0c9179b4ccf..7bac7e46117 100644
--- a/intern/cycles/blender/addon/ui.py
+++ b/intern/cycles/blender/addon/ui.py
@@ -290,6 +290,9 @@ class CYCLES_RENDER_PT_sampling_advanced(CyclesButtonsPanel, Panel):
         col.active = not (cscene.use_adaptive_sampling and cscene.use_preview_adaptive_sampling)
         col.prop(cscene, "sampling_pattern", text="Pattern")
 
+        col = layout.column(align=True)
+        col.prop(cscene, "sample_offset")
+
         layout.separator()
 
         col = layout.column(align=True)
diff --git a/intern/cycles/blender/sync.cpp b/intern/cycles/blender/sync.cpp
index 92662e37bc2..59d684dcf05 100644
--- a/intern/cycles/blender/sync.cpp
+++ b/intern/cycles/blender/sync.cpp
@@ -835,18 +835,25 @@ SessionParams BlenderSync::get_session_params(BL::RenderEngine &b_engine,
   /* samples */
   int samples = get_int(cscene, "samples");
   int preview_samples = get_int(cscene, "preview_samples");
+  int sample_offset = get_int(cscene, "sample_offset");
 
   if (background) {
     params.samples = samples;
+    params.sample_offset = sample_offset;
   }
   else {
     params.samples = preview_samples;
-    if (params.samples == 0)
+    if (params.samples == 0) {
       params.samples = INT_MAX;
+    }
+    params.sample_offset = 0;
   }
 
+  /* Clamp sample offset. */
+  params.sample_offset = clamp(params.sample_offset, 0, Integrator::MAX_SAMPLES);
+
   /* Clamp samples. */
-  params.samples = min(params.samples, Integrator::MAX_SAMPLES);
+  params.samples = clamp(params.samples, 0, Integrator::MAX_SAMPLES - params.sample_offset);
 
   /* Viewport Performance */
   params.pixel_size = b_engine.get_preview_pixel_size(b_scene);