From 7b9e47a35e048071ee6f514ec8aba95caa69a7a8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Foucault?= <foucault.clem@gmail.com>
Date: Sat, 19 Sep 2020 00:24:43 +0200
Subject: EEVEE: Fix Missing GGX multi-scattering on Glass BSDF

Oversight that should have been in rB6f3c279d9e70
---
 .../gpu/shaders/material/gpu_shader_material_glass.glsl   | 15 +++++++++++----
 .../blender/nodes/shader/nodes/node_shader_bsdf_glass.c   | 10 +++++++++-
 2 files changed, 20 insertions(+), 5 deletions(-)

(limited to 'source')

diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_glass.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_glass.glsl
index 6d782ff18de..c328b4800bc 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_glass.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_glass.glsl
@@ -1,6 +1,11 @@
 #ifndef VOLUMETRICS
-void node_bsdf_glass(
-    vec4 color, float roughness, float ior, vec3 N, float ssr_id, out Closure result)
+void node_bsdf_glass(vec4 color,
+                     float roughness,
+                     float ior,
+                     vec3 N,
+                     float use_multiscatter,
+                     float ssr_id,
+                     out Closure result)
 {
   N = normalize(N);
   vec3 out_spec, out_refr, ssr_spec;
@@ -8,7 +13,9 @@ void node_bsdf_glass(
                                               color.rgb; /* Simulate 2 transmission event */
   eevee_closure_glass(N,
                       vec3(1.0),
-                      vec3(1.0),
+                      /* HACK: Pass the multiscatter flag as the sign to not add closure
+                       * variations or increase register usage. */
+                      (use_multiscatter != 0.0) ? vec3(1.0) : -vec3(1.0),
                       int(ssr_id),
                       roughness,
                       1.0,
@@ -28,5 +35,5 @@ void node_bsdf_glass(
 }
 #else
 /* Stub glass because it is not compatible with volumetrics. */
-#  define node_bsdf_glass(a, b, c, d, e, f) (f = CLOSURE_DEFAULT)
+#  define node_bsdf_glass(a, b, c, d, e, f, result) (result = CLOSURE_DEFAULT)
 #endif
diff --git a/source/blender/nodes/shader/nodes/node_shader_bsdf_glass.c b/source/blender/nodes/shader/nodes/node_shader_bsdf_glass.c
index cab25c7ddd0..e0fcce6f617 100644
--- a/source/blender/nodes/shader/nodes/node_shader_bsdf_glass.c
+++ b/source/blender/nodes/shader/nodes/node_shader_bsdf_glass.c
@@ -51,7 +51,15 @@ static int node_shader_gpu_bsdf_glass(GPUMaterial *mat,
 
   GPU_material_flag_set(mat, GPU_MATFLAG_GLOSSY | GPU_MATFLAG_REFRACT);
 
-  return GPU_stack_link(mat, node, "node_bsdf_glass", in, out, GPU_constant(&node->ssr_id));
+  float use_multi_scatter = (node->custom1 == SHD_GLOSSY_MULTI_GGX) ? 1.0f : 0.0f;
+
+  return GPU_stack_link(mat,
+                        node,
+                        "node_bsdf_glass",
+                        in,
+                        out,
+                        GPU_constant(&use_multi_scatter),
+                        GPU_constant(&node->ssr_id));
 }
 
 /* node type definition */
-- 
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