Fix T97921: Cycles MNEE issue with light path nodes

Ensure the correct total/diffuse/transmission depth is set when evaluating
shaders for MNEE, consistent with regular light shader evaluation.

Differential Revision: https://developer.blender.org/D14902

2 files changed, 30 insertions, 6 deletions

diff --git a/intern/cycles/kernel/integrator/mnee.h b/intern/cycles/kernel/integrator/mnee.h
index 7b86c660380..e924f408d59 100644
--- a/intern/cycles/kernel/integrator/mnee.h
+++ b/intern/cycles/kernel/integrator/mnee.h
@@ -813,6 +813,15 @@ ccl_device_forceinline bool mnee_path_contribution(KernelGlobals kg,
    * and keep pdf in vertex area measure */
   mnee_update_light_sample(kg, vertices[vertex_count - 1].p, ls);
 
+  /* Save state path bounce info in case a light path node is used in the refractive interface or
+   * light shader graph. */
+  const int transmission_bounce = INTEGRATOR_STATE(state, path, transmission_bounce);
+  const int diffuse_bounce = INTEGRATOR_STATE(state, path, diffuse_bounce);
+  const int bounce = INTEGRATOR_STATE(state, path, bounce);
+
+  /* Set diffuse bounce info . */
+  INTEGRATOR_STATE_WRITE(state, path, diffuse_bounce) = diffuse_bounce + 1;
+
   /* Evaluate light sample
    * in case the light has a node-based shader:
    * 1. sd_mnee will be used to store light data, which is why we need to do
@@ -820,6 +829,12 @@ ccl_device_forceinline bool mnee_path_contribution(KernelGlobals kg,
    *    interface data at the end of the call for the shadow ray setup to work.
    * 2. ls needs to contain the last interface data for the light shader to
    *    evaluate properly */
+
+  /* Set bounce info in case a light path node is used in the light shader graph. */
+  INTEGRATOR_STATE_WRITE(state, path, transmission_bounce) = transmission_bounce + vertex_count -
+                                                             1;
+  INTEGRATOR_STATE_WRITE(state, path, bounce) = bounce + vertex_count;
+
   float3 light_eval = light_sample_shader_eval(kg, state, sd_mnee, ls, sd->time);
   bsdf_eval_mul3(throughput, light_eval / ls->pdf);
 
@@ -891,6 +906,11 @@ ccl_device_forceinline bool mnee_path_contribution(KernelGlobals kg,
                              false,
                              LAMP_NONE);
 
+    /* Set bounce info in case a light path node is used in the refractive interface
+     * shader graph. */
+    INTEGRATOR_STATE_WRITE(state, path, transmission_bounce) = transmission_bounce + vi;
+    INTEGRATOR_STATE_WRITE(state, path, bounce) = bounce + 1 + vi;
+
     /* Evaluate shader nodes at solution vi. */
     shader_eval_surface<KERNEL_FEATURE_NODE_MASK_SURFACE_SHADOW>(
         kg, state, sd_mnee, NULL, PATH_RAY_DIFFUSE, true);
@@ -907,6 +927,11 @@ ccl_device_forceinline bool mnee_path_contribution(KernelGlobals kg,
     bsdf_eval_mul3(throughput, bsdf_contribution);
   }
 
+  /* Restore original state path bounce info. */
+  INTEGRATOR_STATE_WRITE(state, path, transmission_bounce) = transmission_bounce;
+  INTEGRATOR_STATE_WRITE(state, path, diffuse_bounce) = diffuse_bounce;
+  INTEGRATOR_STATE_WRITE(state, path, bounce) = bounce;
+
   return true;
 }
 
@@ -1036,18 +1061,17 @@ ccl_device_forceinline int kernel_path_mnee_sample(KernelGlobals kg,
     return 0;
 
   /* Check whether the transmission depth limit is reached before continuing. */
-  if (INTEGRATOR_STATE(state, path, transmission_bounce) + vertex_count >=
+  if ((INTEGRATOR_STATE(state, path, transmission_bounce) + vertex_count - 1) >=
       kernel_data.integrator.max_transmission_bounce)
     return 0;
 
   /* Check whether the diffuse depth limit is reached before continuing. */
-  if (INTEGRATOR_STATE(state, path, diffuse_bounce) + 1 >=
+  if ((INTEGRATOR_STATE(state, path, diffuse_bounce) + 1) >=
       kernel_data.integrator.max_diffuse_bounce)
     return 0;
 
   /* Check whether the overall depth limit is reached before continuing. */
-  if (INTEGRATOR_STATE(state, path, bounce) + 1 + vertex_count >=
-      kernel_data.integrator.max_bounce)
+  if ((INTEGRATOR_STATE(state, path, bounce) + vertex_count) >= kernel_data.integrator.max_bounce)
     return 0;
 
   /* Mark the manifold walk valid to turn off mollification regardless of how successful the walk
diff --git a/intern/cycles/kernel/integrator/shade_surface.h b/intern/cycles/kernel/integrator/shade_surface.h
index 859c314b088..896e81b80ff 100644
--- a/intern/cycles/kernel/integrator/shade_surface.h
+++ b/intern/cycles/kernel/integrator/shade_surface.h
@@ -253,13 +253,13 @@ ccl_device_forceinline void integrate_surface_direct_light(KernelGlobals kg,
 #  ifdef __MNEE__
   if (mnee_vertex_count > 0) {
     INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, transmission_bounce) =
-        INTEGRATOR_STATE(state, path, transmission_bounce) + mnee_vertex_count;
+        INTEGRATOR_STATE(state, path, transmission_bounce) + mnee_vertex_count - 1;
     INTEGRATOR_STATE_WRITE(shadow_state,
                            shadow_path,
                            diffuse_bounce) = INTEGRATOR_STATE(state, path, diffuse_bounce) + 1;
     INTEGRATOR_STATE_WRITE(shadow_state,
                            shadow_path,
-                           bounce) = INTEGRATOR_STATE(state, path, bounce) + 1 + mnee_vertex_count;
+                           bounce) = INTEGRATOR_STATE(state, path, bounce) + mnee_vertex_count;
   }
   else
 #  endif