[D3D12] 128 megatexel limit explanation based on the spec [ci skip]

src/xenia/gpu/d3d12/d3d12_render_target_cache.cc

@@ -1413,8 +1413,9 @@ bool D3D12RenderTargetCache::Resolve(const Memory& memory,
       if (copy_dest_committed) {
         // Write the descriptors and transition the resources.
         // Full shared memory without resolution scaling, range of the scaled
-        // resolve buffer with scaling because only 128 R32 elements can be
-        // addressed on Nvidia.
+        // resolve buffer with scaling because only at least 128 * 2^20 R32
+        // elements must be addressable
+        // (D3D12_REQ_BUFFER_RESOURCE_TEXEL_COUNT_2_TO_EXP).
         ui::d3d12::util::DescriptorCpuGpuHandlePair descriptor_dest;
         ui::d3d12::util::DescriptorCpuGpuHandlePair descriptor_source;
         ui::d3d12::util::DescriptorCpuGpuHandlePair descriptors[2];

src/xenia/gpu/d3d12/d3d12_shared_memory.h

@@ -76,8 +76,8 @@ class D3D12SharedMemory : public SharedMemory {
 
   void WriteRawSRVDescriptor(D3D12_CPU_DESCRIPTOR_HANDLE handle);
   void WriteRawUAVDescriptor(D3D12_CPU_DESCRIPTOR_HANDLE handle);
-  // Due to the Nvidia 128 megatexel limitation, the smallest supported formats
-  // are 32-bit.
+  // Due to the D3D12_REQ_BUFFER_RESOURCE_TEXEL_COUNT_2_TO_EXP limitation, the
+  // smallest supported formats are 32-bit.
   void WriteUintPow2SRVDescriptor(D3D12_CPU_DESCRIPTOR_HANDLE handle,
                                   uint32_t element_size_bytes_pow2);
   void WriteUintPow2UAVDescriptor(D3D12_CPU_DESCRIPTOR_HANDLE handle,

src/xenia/gpu/d3d12/d3d12_texture_cache.cc

@@ -1715,9 +1715,10 @@ bool D3D12TextureCache::LoadTextureDataFromResidentMemoryImpl(Texture& texture,
   }
 
   // Begin loading.
-  // May use different buffers for scaled base and mips, and also can't address
-  // more than 128 megatexels directly on Nvidia - need two separate UAV
-  // descriptors for base and mips.
+  // May use different buffers for scaled base and mips, and also addressability
+  // of more than 128 * 2^20 (2^D3D12_REQ_BUFFER_RESOURCE_TEXEL_COUNT_2_TO_EXP)
+  // texels is not mandatory - need two separate UAV descriptors for base and
+  // mips.
   // Destination.
   uint32_t descriptor_count = 1;
   if (texture_resolution_scaled) {
@@ -1820,7 +1821,8 @@ bool D3D12TextureCache::LoadTextureDataFromResidentMemoryImpl(Texture& texture,
 
     if (texture_resolution_scaled) {
       // Offset already applied in the buffer because more than 512 MB can't be
-      // directly addresses on Nvidia as R32.
+      // directly addresses as R32 on some hardware (above
+      // 2^D3D12_REQ_BUFFER_RESOURCE_TEXEL_COUNT_2_TO_EXP).
       load_constants.guest_offset = 0;
     } else {
       load_constants.guest_offset = guest_address;

src/xenia/gpu/draw_util.h

@@ -377,7 +377,8 @@ struct ResolveCopyShaderInfo {
   // shader (at least 2).
   uint32_t source_bpe_log2;
   // Log2 of bytes per element of the type of the destination buffer bound to
-  // the shader (at least 2 because of Nvidia's 128 megatexel limit that
+  // the shader (at least 2 because of the 128 megatexel minimum requirement on
+  // Direct3D 10+ - D3D12_REQ_BUFFER_RESOURCE_TEXEL_COUNT_2_TO_EXP - that
   // prevents binding the entire shared memory buffer with smaller element
   // sizes).
   uint32_t dest_bpe_log2;

src/xenia/gpu/dxbc_shader_translator_memexport.cc

@@ -18,12 +18,13 @@ namespace gpu {
 using namespace ucode;
 
 // TODO(Triang3l): Support sub-dword memexports (like k_8 in 58410B86). This
-// would require four 128 MB R8_UINT UAVs due to the Nvidia addressing limit.
-// Need to be careful with resource binding tiers, however. Resource binding
-// tier 1 on feature level 11_0 allows only 8 UAVs _across all stages_.
-// RWByteAddressBuffer + 4 typed buffers is 5 per stage already, would need 10
-// for both VS and PS, or even 11 with the eDRAM ROV. Need to drop draw commands
-// doing memexport in both VS and PS on FL 11_0 resource binding tier 1.
+// would require four 128 MB R8_UINT UAVs due to
+// D3D12_REQ_BUFFER_RESOURCE_TEXEL_COUNT_2_TO_EXP. Need to be careful with
+// resource binding tiers, however. Resource binding tier 1 on feature level
+// 11_0 allows only 8 UAVs _across all stages_. RWByteAddressBuffer + 4 typed
+// buffers is 5 per stage already, would need 10 for both VS and PS, or even 11
+// with the eDRAM ROV. Need to drop draw commands doing memexport in both VS and
+// PS on FL 11_0 resource binding tier 1.
 
 void DxbcShaderTranslator::ExportToMemory_PackFixed32(
     const uint32_t* eM_temps, uint32_t eM_count, const uint32_t bits[4],