Cycles: First implementation of shadow catcher

It uses an idea of accumulating all possible light reachable across the
light path (without taking shadow blocked into account) and accumulating
total shaded light across the path. Dividing second figure by first one
seems to be giving good estimate of the shadow.

In fact, to my knowledge, it's something really similar to what is
happening in the denoising branch, so we are aligned here which is good.

The workflow is following:

- Create an object which matches real-life object on which shadow is
  to be catched.

- Create approximate similar material on that object.

  This is needed to make indirect light properly affecting CG objects
  in the scene.

- Mark object as Shadow Catcher in the Object properties.

Ideally, after doing that it will be possible to render the image and
simply alpha-over it on top of real footage.

1 files changed, 1 insertions, 0 deletions

diff --git a/intern/cycles/render/object.h b/intern/cycles/render/object.h
index 3495849d149..dabe0f71662 100644
--- a/intern/cycles/render/object.h
+++ b/intern/cycles/render/object.h
@@ -53,6 +53,7 @@ public:
 	bool use_motion;
 	bool hide_on_missing_motion;
 	bool use_holdout;
+	bool is_shadow_catcher;
 
 	float3 dupli_generated;
 	float2 dupli_uv;