Fix: Cycles hardware RT is only supported if all multi devices have it

Pull Request: https://projects.blender.org/blender/blender/pulls/135179

intern/cycles/blender/addon/properties.py

@@ -1835,16 +1835,26 @@ class CyclesPreferences(bpy.types.AddonPreferences):
         self._draw_devices(row, compute_device_type, devices)
 
         import _cycles
-        has_peer_memory = 0
-        has_rt_api_support = {'METAL': False, 'HIP': False, 'ONEAPI': False}
+        has_peer_memory = False
+        has_enabled_hardware_rt = False
+        has_disabled_hardware_rt = False
         for device in self.get_device_list(compute_device_type):
-            if device[3] and self.find_existing_device_entry(device).use:
-                has_peer_memory += 1
-            if device[4] and self.find_existing_device_entry(device).use:
-                device_type = device[1]
-                has_rt_api_support[device_type] = True
+            if not self.find_existing_device_entry(device).use:
+                continue
+            if device[1] != compute_device_type:
+                continue
 
-        if has_peer_memory > 1:
+            if device[3]:
+                has_peer_memory = True
+            if device[4]:
+                has_enabled_hardware_rt = True
+            else:
+                has_disabled_hardware_rt = True
+
+        # Any device without RT support will disable it for all.
+        has_hardware_rt = has_enabled_hardware_rt and not has_disabled_hardware_rt
+
+        if has_peer_memory:
             row = layout.row()
             row.use_property_split = True
             row.prop(self, "peer_memory")
@@ -1857,18 +1867,19 @@ class CyclesPreferences(bpy.types.AddonPreferences):
                 col = layout.column()
                 col.use_property_split = True
                 col.prop(self, "kernel_optimization_level")
-                if has_rt_api_support['METAL']:
-                    col.prop(self, "metalrt")
+                row = col.row()
+                row.active = has_hardware_rt
+                row.prop(self, "metalrt")
 
         if compute_device_type == 'HIP':
             import platform
             row = layout.row()
-            row.active = has_rt_api_support['HIP']
+            row.active = has_hardware_rt
             row.prop(self, "use_hiprt")
 
         elif compute_device_type == 'ONEAPI' and _cycles.with_embree_gpu:
             row = layout.row()
-            row.active = has_rt_api_support['ONEAPI']
+            row.active = has_hardware_rt
             row.prop(self, "use_oneapirt")
 
     def draw(self, context):

intern/cycles/blender/device.cpp

@@ -63,13 +63,6 @@ static void adjust_device_info(DeviceInfo &device, PointerRNA cpreferences, bool
   adjust_device_info_from_preferences(device, cpreferences);
   for (DeviceInfo &info : device.multi_devices) {
     adjust_device_info_from_preferences(info, cpreferences);
-
-    /* There is an accumulative logic here, because Multi-devices are supported only for
-     * the same backend + CPU in Blender right now, and both oneAPI and Metal have a
-     * global boolean backend setting for enabling/disabling Hardware Ray Tracing,
-     * so all sub-devices in the multi-device should enable (or disable) Hardware Ray Tracing
-     * simultaneously (and CPU device is expected to ignore `use_hardware_raytracing` setting). */
-    device.use_hardware_raytracing |= info.use_hardware_raytracing;
   }
 
   if (preview) {

intern/cycles/device/multi/device.cpp

@@ -31,10 +31,12 @@ class MultiDevice : public Device {
   device_ptr unique_key = 1;
   vector<vector<SubDevice *>> peer_islands;
 
-  MultiDevice(const DeviceInfo &info, Stats &stats, Profiler &profiler, bool headless)
-      : Device(info, stats, profiler, headless)
+  MultiDevice(const DeviceInfo &info_, Stats &stats, Profiler &profiler, bool headless)
+      : Device(info_, stats, profiler, headless)
   {
-    for (const DeviceInfo &subinfo : info.multi_devices) {
+    verify_hardware_raytracing();
+
+    for (const DeviceInfo &subinfo : this->info.multi_devices) {
       /* Always add CPU devices at the back since GPU devices can change
        * host memory pointers, which CPU uses as device pointer. */
       SubDevice *sub;
@@ -78,6 +80,34 @@ class MultiDevice : public Device {
     }
   }
 
+  void verify_hardware_raytracing()
+  {
+    /* Determine if we can use hardware ray-tracing. It is only supported if all selected
+     * GPU devices support it. Both the backends and scene update code do not support mixed
+     * BVH2 and hardware raytracing. The CPU device will ignore this setting. */
+    bool have_disabled_hardware_rt = false;
+    bool have_enabled_hardware_rt = false;
+
+    for (const DeviceInfo &subinfo : info.multi_devices) {
+      if (subinfo.type != DEVICE_CPU) {
+        if (subinfo.use_hardware_raytracing) {
+          have_enabled_hardware_rt = true;
+        }
+        else {
+          have_disabled_hardware_rt = true;
+        }
+      }
+    }
+
+    info.use_hardware_raytracing = have_enabled_hardware_rt && !have_disabled_hardware_rt;
+
+    for (DeviceInfo &subinfo : info.multi_devices) {
+      if (subinfo.type != DEVICE_CPU) {
+        subinfo.use_hardware_raytracing = info.use_hardware_raytracing;
+      }
+    }
+  }
+
   const string &error_message() override
   {
     error_msg.clear();