Fix T92462: Cycles crash calculating hair transparency

Need to make sure images needed for hair shaders are loaded
before running the shader.

The naming is a bit misleading, but this is an internal API
and we can change it easily. Submitting minimal patch needed
to fix logic in the code to make it safer to review for 3.0.

Differential Revision: https://developer.blender.org/D13067

1 files changed, 12 insertions, 1 deletions

diff --git a/intern/cycles/scene/geometry.cpp b/intern/cycles/scene/geometry.cpp
index 5141e1f8358..8a3fc522d22 100644
--- a/intern/cycles/scene/geometry.cpp
+++ b/intern/cycles/scene/geometry.cpp
@@ -1588,9 +1588,20 @@ void GeometryManager::device_update_displacement_images(Device *device,
   set<int> bump_images;
   foreach (Geometry *geom, scene->geometry) {
     if (geom->is_modified()) {
+      /* Geometry-level check for hair shadow transparency.
+       * This matches the logic in the `Hair::update_shadow_transparency()`, avoiding access to
+       * possible non-loaded images. */
+      bool need_shadow_transparency = false;
+      if (geom->geometry_type == Geometry::HAIR) {
+        Hair *hair = static_cast<Hair *>(geom);
+        need_shadow_transparency = hair->need_shadow_transparency();
+      }
+
       foreach (Node *node, geom->get_used_shaders()) {
         Shader *shader = static_cast<Shader *>(node);
-        if (!shader->has_displacement || shader->get_displacement_method() == DISPLACE_BUMP) {
+        const bool is_true_displacement = (shader->has_displacement &&
+                                           shader->get_displacement_method() != DISPLACE_BUMP);
+        if (!is_true_displacement && !need_shadow_transparency) {
           continue;
         }
         foreach (ShaderNode *node, shader->graph->nodes) {