Fix SYCL/ICX warnings in tutorial SYCL device code

Three classes of warning fixed, all from the ICX SYCL device compiler:

1. [-Wundefined-internal] sycl::detail::get_spec_constant_symbolic_ID
   has internal linkage but is not defined.

   'const' variables at C++ namespace scope have *internal* linkage by
   default (same as 'static const').  The SYCL compiler generates a
   per-variable helper function with matching linkage; when that linkage
   is internal the function has no definition visible to the SYCL
   runtime and the warning fires.

   Fix: declare all sycl::specialization_id objects as 'inline const'.
   C++17 inline variables have external linkage, so the compiler emits
   one uniquely-identifiable definition.  viewer_device_debug.cpp
   re-declares the same spec_feature_mask as inline const; the ODR
   rule merges it with viewer_device.cpp's definition at link time.

   Files changed: viewer_device.cpp, viewer_device_debug.cpp,
                  next_hit_device.cpp, pathtracer_device.cpp

2. [-Wuninitialized-const-pointer] imgui_widgets.cpp: 'empty_string'
   passed as a const-pointer before being initialised.

   Fix: zero-initialise the STB_TEXTEDIT_CHARTYPE variable at the point
   of declaration.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stefanatwork

tutorials/common/imgui/imgui_widgets.cpp

@@ -4439,7 +4439,7 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
                 // Clear input
                 apply_new_text = "";
                 apply_new_text_length = 0;
-                STB_TEXTEDIT_CHARTYPE empty_string;
+                STB_TEXTEDIT_CHARTYPE empty_string = 0;
                 stb_textedit_replace(state, &state->Stb, &empty_string, 0);
             }
             else if (strcmp(buf, state->InitialTextA.Data) != 0)

tutorials/next_hit/next_hit_device.cpp

@@ -17,7 +17,7 @@ RTCScene g_scene = nullptr;
 TutorialData data;
 
 #if defined(EMBREE_SYCL_TUTORIAL) && !defined(EMBREE_SYCL_RT_SIMULATION) && defined(USE_SPECIALIZATION_CONSTANTS)
-static const sycl::specialization_id<RTCFeatureFlags> spec_feature_mask;
+inline const sycl::specialization_id<RTCFeatureFlags> spec_feature_mask;
 #endif
 
 RTCFeatureFlags g_feature_mask;

tutorials/pathtracer/pathtracer_device.cpp

@@ -39,7 +39,7 @@ bool g_subdiv_mode = false;
 unsigned int keyframeID = 0;
 
 #if defined(EMBREE_SYCL_TUTORIAL) && !defined(EMBREE_SYCL_RT_SIMULATION) && defined(USE_SPECIALIZATION_CONSTANTS)
-const static sycl::specialization_id<RTCFeatureFlags> rtc_feature_mask(RTC_FEATURE_FLAG_ALL);
+inline const sycl::specialization_id<RTCFeatureFlags> rtc_feature_mask(RTC_FEATURE_FLAG_ALL);
 #endif
 RTCFeatureFlags g_used_features = RTC_FEATURE_FLAG_NONE;
 

tutorials/viewer/viewer_device.cpp

@@ -10,7 +10,7 @@ extern "C" bool g_changed;
 TutorialData data;
 
 #if defined(EMBREE_SYCL_TUTORIAL) && !defined(EMBREE_SYCL_RT_SIMULATION) && defined(USE_SPECIALIZATION_CONSTANTS)
-const sycl::specialization_id<RTCFeatureFlags> spec_feature_mask;
+inline const sycl::specialization_id<RTCFeatureFlags> spec_feature_mask;
 #endif
 
 extern "C" RTCFeatureFlags g_feature_mask;

tutorials/viewer/viewer_device_debug.cpp

@@ -19,7 +19,7 @@ extern "C" bool g_changed;
 extern "C" float g_debug;
 
 #if defined(EMBREE_SYCL_TUTORIAL) && !defined(EMBREE_SYCL_RT_SIMULATION)
-static const sycl::specialization_id<RTCFeatureFlags> spec_feature_mask;
+inline const sycl::specialization_id<RTCFeatureFlags> spec_feature_mask;
 #endif
 
 extern "C" RTCFeatureFlags g_feature_mask;