Cycles: Initialize the RNG state from the kernel instead of the host

This allows to save a memory copy, which will be particularly useful for network rendering.

Reviewers: sergey, brecht, dingto, juicyfruit, maiself

Differential Revision: https://developer.blender.org/D2323

intern/cycles/kernel/kernel_path_common.h

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include "util_hash.h"
+
 CCL_NAMESPACE_BEGIN
 
 ccl_device_inline void kernel_path_trace_setup(KernelGlobals *kg,
@@ -28,6 +30,10 @@ ccl_device_inline void kernel_path_trace_setup(KernelGlobals *kg,
 
 	int num_samples = kernel_data.integrator.aa_samples;
 
+	if(sample == 0) {
+		*rng_state = hash_int_2d(x, y);
+	}
+
 	path_rng_init(kg, rng_state, sample, num_samples, rng, x, y, &filter_u, &filter_v);
 
 	/* sample camera ray */