Cycles: option to make background visible through glass transparent.

This can be enabled in the Film panel, with an option to control the
transmisison roughness below which glass becomes transparent.

Differential Revision: https://developer.blender.org/D2904

1 files changed, 12 insertions, 1 deletions

diff --git a/intern/cycles/kernel/closure/bsdf.h b/intern/cycles/kernel/closure/bsdf.h
index e4573024e85..6f0bdb3fa38 100644
--- a/intern/cycles/kernel/closure/bsdf.h
+++ b/intern/cycles/kernel/closure/bsdf.h
@@ -38,7 +38,7 @@ CCL_NAMESPACE_BEGIN
 
 /* Returns the square of the roughness of the closure if it has roughness,
  * 0 for singular closures and 1 otherwise. */
-ccl_device_inline float bsdf_get_roughness_sqr(const ShaderClosure *sc)
+ccl_device_inline float bsdf_get_roughness_squared(const ShaderClosure *sc)
 {
 	if(CLOSURE_IS_BSDF_SINGULAR(sc->type)) {
 		return 0.0f;
@@ -173,6 +173,17 @@ ccl_device_forceinline int bsdf_sample(KernelGlobals *kg,
 			break;
 	}
 
+	/* Test if BSDF sample should be treated as transparent for background. */
+	if(label & LABEL_TRANSMIT) {
+		float threshold_squared = kernel_data.background.transparent_roughness_squared_threshold;
+
+		if(threshold_squared >= 0.0f) {
+			if(bsdf_get_roughness_squared(sc) <= threshold_squared) {
+				label |= LABEL_TRANSMIT_TRANSPARENT;
+			}
+		}
+	}
+
 	return label;
 }