From: d4r
Subject: [PATCH] null texture objects read as zero

CUDA texture object 0 reads as zeros on NVIDIA GPUs, and DLSS samples absent optional inputs
(its exposure scales, with the flags Ghost of Tsushima uses) that way. A ZLUDA texture object is a
descriptor pointer, so handle 0 made the GPU read address 0 and fault. Handle 0 now points at an
all-zero descriptor, which AMD hardware treats as a null resource. Rebuild ptx/lib/*.bc after
applying (scripts/build_zluda_ptx_helpers.sh).
---
--- a/ptx/lib/zluda_ptx_impl.cpp	2026-09-27 16:47:02.815623944 -0400
+++ b/ptx/lib/zluda_ptx_impl.cpp	2026-09-27 16:47:02.815623944 -0400
@@ -1725,9 +1725,18 @@
                c;
     }
 
+    // d4r: CUDA texture object 0 reads as zeros on NVIDIA GPUs, and DLSS samples absent optional inputs
+    // (exposure scales) that way. A ZLUDA texture object is a descriptor pointer, so 0 is redirected to
+    // an all-zero descriptor, which AMD hardware treats as a null resource (reads return 0).
+    __device__ static unsigned int d4r_null_texture[32];
+    static uint64_t texture_or_null(uint64_t texobj) __device__
+    {
+        return texobj != 0 ? texobj : uint64_t(uintptr_t(d4r_null_texture));
+    }
+
     static std::pair<GLOBAL_SPACE void *, GLOBAL_SPACE void *> get_image_and_sampler(uint64_t texobj) __device__
     {
-        unsigned int GLOBAL_SPACE *image = (unsigned int GLOBAL_SPACE *)texobj;
+        unsigned int GLOBAL_SPACE *image = (unsigned int GLOBAL_SPACE *)texture_or_null(texobj);
         unsigned int GLOBAL_SPACE *sampler = image + HIP_SAMPLER_OBJECT_OFFSET_DWORD;
         return {image, sampler};
     }
@@ -1868,7 +1877,7 @@
 #define tex_2d_gather4(COMPONENT)                                                                                                     \
     v4f32 FUNC(texobj_gather4##COMPONENT##_2d_v4_f32_f32)(uint64_t texobj, v2f32 coord)                                              \
     {                                                                                                                                  \
-        auto image = reinterpret_cast<unsigned int CONSTANT_SPACE *>(static_cast<uintptr_t>(texobj));                                 \
+        auto image = reinterpret_cast<unsigned int CONSTANT_SPACE *>(static_cast<uintptr_t>(texture_or_null(texobj)));                                 \
         auto sampler = image + HIP_SAMPLER_OBJECT_OFFSET_DWORD;                                                                        \
         float2 coordinates{coord.x, coord.y};                                                                                          \
         auto result = __ockl_image_gather4##COMPONENT##_2D(image, sampler, get_native_vector(coordinates));                           \