Cycles: Resumable render implementation for Cycles

This feature is also known by the name Samples Offset, which allows
artists to render animation with given amount of samples N, but then
render more samples, starting from N and ending with M (where M > N)
and merge renders together as if they rendered exactly M samples.

Surely such effect could be achieved by changing Seed variable, but
that has possible issues with correlation artifacts and requiring to
manually deal with per render layer samples and such.

While we can't support all possible renderfarm-related features in
Cycles it's nice to support really commonly used stuff.

Here's a command how to run Blender with the new feature enabled:

  blender -- --cycles-resumable-num-chunks 24 --cycles-resumable-current-chunk 2

This command will divide samples range in 24 parts and render
range #2 (chunk number is 1-based).

This feature might be changed a bit after we'll do some tests here
in the studio with it.

1 files changed, 11 insertions, 0 deletions

diff --git a/intern/cycles/render/tile.h b/intern/cycles/render/tile.h
index 700e00c9e0a..af1b1ed8b0f 100644
--- a/intern/cycles/render/tile.h
+++ b/intern/cycles/render/tile.h
@@ -82,6 +82,17 @@ public:
 	bool done();
 
 	void set_tile_order(TileOrder tile_order_) { tile_order = tile_order_; }
+
+	/* ** Sample range rendering. ** */
+
+	/* Start sample in the range. */
+	int range_start_sample;
+
+	/* Number to samples in the rendering range. */
+	int range_num_samples;
+
+	/* get number of actual samples to render. */
+	int get_num_effective_samples();
 protected:
 
 	void set_tiles();