Fix T97985 EEVEE: Shader mixing not working correctly when reusing shader nodes

This was caused by the `Closure` members being added to the final contribution
more than once. The workaround is to clear the members once a closure has
been added to the final contribution. I used `inout` on `Closure` inputs
so that the render engine implementation of mix and add closure nodes
can do its own thing. The nodegraph handling of inout was changed for this
to work.

6 files changed, 13 insertions, 10 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/closure_eval_surface_lib.glsl b/source/blender/draw/engines/eevee/shaders/closure_eval_surface_lib.glsl
index f85ef4a89a4..0f5290a7c07 100644
--- a/source/blender/draw/engines/eevee/shaders/closure_eval_surface_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/closure_eval_surface_lib.glsl
@@ -309,16 +309,19 @@ vec4 closure_to_rgba(Closure closure)
   return vec4(closure.radiance, 1.0 - saturate(avg(closure.transmittance)));
 }
 
-Closure closure_add(Closure cl1, Closure cl2)
+Closure closure_add(inout Closure cl1, inout Closure cl2)
 {
   Closure cl;
   cl.radiance = cl1.radiance + cl2.radiance;
   cl.transmittance = cl1.transmittance + cl2.transmittance;
   cl.holdout = cl1.holdout + cl2.holdout;
+  /* Make sure each closure is only added once to the result. */
+  cl1 = CLOSURE_DEFAULT;
+  cl2 = CLOSURE_DEFAULT;
   return cl;
 }
 
-Closure closure_mix(Closure cl1, Closure cl2, float fac)
+Closure closure_mix(inout Closure cl1, inout Closure cl2, float fac)
 {
   /* Weights have already been applied. */
   return closure_add(cl1, cl2);
diff --git a/source/blender/draw/engines/eevee/shaders/closure_eval_volume_lib.glsl b/source/blender/draw/engines/eevee/shaders/closure_eval_volume_lib.glsl
index e450b8ad3c8..5e34d654cfd 100644
--- a/source/blender/draw/engines/eevee/shaders/closure_eval_volume_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/closure_eval_volume_lib.glsl
@@ -92,7 +92,7 @@ vec4 closure_to_rgba(Closure closure)
   return vec4(0.0);
 }
 
-Closure closure_mix(Closure cl1, Closure cl2, float fac)
+Closure closure_mix(inout Closure cl1, inout Closure cl2, float fac)
 {
   Closure cl;
   cl.absorption = mix(cl1.absorption, cl2.absorption, fac);
@@ -102,7 +102,7 @@ Closure closure_mix(Closure cl1, Closure cl2, float fac)
   return cl;
 }
 
-Closure closure_add(Closure cl1, Closure cl2)
+Closure closure_add(inout Closure cl1, inout Closure cl2)
 {
   Closure cl;
   cl.absorption = cl1.absorption + cl2.absorption;
diff --git a/source/blender/draw/engines/eevee/shaders/closure_type_lib.glsl b/source/blender/draw/engines/eevee/shaders/closure_type_lib.glsl
index 9698b5ea6f5..21d347942ca 100644
--- a/source/blender/draw/engines/eevee/shaders/closure_type_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/closure_type_lib.glsl
@@ -87,8 +87,8 @@ Closure closure_eval(ClosureDiffuse diffuse,
                      ClosureReflection clearcoat,
                      ClosureRefraction refraction);
 
-Closure closure_add(Closure cl1, Closure cl2);
-Closure closure_mix(Closure cl1, Closure cl2, float fac);
+Closure closure_add(inout Closure cl1, inout Closure cl2);
+Closure closure_mix(inout Closure cl1, inout Closure cl2, float fac);
 
 float ambient_occlusion_eval(vec3 normal,
                              float distance,
diff --git a/source/blender/gpu/intern/gpu_node_graph.c b/source/blender/gpu/intern/gpu_node_graph.c
index bc7ace792bb..b3a091ffbb0 100644
--- a/source/blender/gpu/intern/gpu_node_graph.c
+++ b/source/blender/gpu/intern/gpu_node_graph.c
@@ -611,7 +611,7 @@ bool GPU_link(GPUMaterial *mat, const char *name, ...)
 
   va_start(params, name);
   for (i = 0; i < function->totparam; i++) {
-    if (function->paramqual[i] != FUNCTION_QUAL_IN) {
+    if (function->paramqual[i] == FUNCTION_QUAL_OUT) {
       linkptr = va_arg(params, GPUNodeLink **);
       gpu_node_output(node, function->paramtype[i], linkptr);
     }
@@ -669,7 +669,7 @@ static bool gpu_stack_link_v(GPUMaterial *material,
   }
 
   for (i = 0; i < function->totparam; i++) {
-    if (function->paramqual[i] != FUNCTION_QUAL_IN) {
+    if (function->paramqual[i] == FUNCTION_QUAL_OUT) {
       if (totout == 0) {
         linkptr = va_arg(params, GPUNodeLink **);
         gpu_node_output(node, function->paramtype[i], linkptr);
diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_add_shader.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_add_shader.glsl
index 99117400c57..3f42b6d9094 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_add_shader.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_add_shader.glsl
@@ -1,4 +1,4 @@
-void node_add_shader(Closure shader1, Closure shader2, out Closure shader)
+void node_add_shader(inout Closure shader1, inout Closure shader2, out Closure shader)
 {
   shader = closure_add(shader1, shader2);
 }
diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_mix_shader.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_mix_shader.glsl
index c303d21d7c1..00cfba3ca12 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_mix_shader.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_mix_shader.glsl
@@ -1,4 +1,4 @@
-void node_mix_shader(float fac, Closure shader1, Closure shader2, out Closure shader)
+void node_mix_shader(float fac, inout Closure shader1, inout Closure shader2, out Closure shader)
 {
   shader = closure_mix(shader1, shader2, fac);
 }