Refactor vulkan PostVS fetch to use compute instead of vertex stores

* Mobile chips are lacking in features, particularly
  vertexPipelineStoresAndAtomics which is needed to manually emulate
  stream-out with shader patching.
* Instead we change to transform the vertex shader into a compute shader
  and dispatch it to manually fetch the vertex inputs, run the original
  shader, and store the resulting outputs.

renderdoc/driver/vulkan/vk_debug.cpp

@@ -1337,8 +1337,20 @@ void VulkanReplay::CreateResources()
 
   WrappedVulkan *driver = m_pDriver;
 
-  CREATE_OBJECT(m_MeshFetchDescSetLayout,
-                {{0, VK_DESCRIPTOR_TYPE_STORAGE_BUFFER, 1, VK_SHADER_STAGE_ALL, NULL}});
+  CREATE_OBJECT(
+      m_MeshFetchDescSetLayout,
+      {
+          // output buffer
+          {0, VK_DESCRIPTOR_TYPE_STORAGE_BUFFER, 1, VK_SHADER_STAGE_COMPUTE_BIT, NULL},
+          // index buffer (if needed)
+          {1, VK_DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER, 1, VK_SHADER_STAGE_COMPUTE_BIT, NULL},
+          // vertex buffers (float type)
+          {2, VK_DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER, 16, VK_SHADER_STAGE_COMPUTE_BIT, NULL},
+          // vertex buffers (uint32_t type)
+          {3, VK_DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER, 16, VK_SHADER_STAGE_COMPUTE_BIT, NULL},
+          // vertex buffers (int32_t type)
+          {4, VK_DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER, 16, VK_SHADER_STAGE_COMPUTE_BIT, NULL},
+      });
 
   CREATE_OBJECT(m_MeshFetchDescSet, m_General.DescriptorPool, m_MeshFetchDescSetLayout);
 }
@@ -1367,6 +1379,7 @@ void VulkanReplay::GeneralMisc::Init(WrappedVulkan *driver, VkDescriptorPool des
       {VK_DESCRIPTOR_TYPE_STORAGE_IMAGE, 32},
       {VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER, 128},
       {VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER_DYNAMIC, 128},
+      {VK_DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER, 64},
       {VK_DESCRIPTOR_TYPE_STORAGE_BUFFER, 32},
   };
 

renderdoc/driver/vulkan/vk_replay.h

@@ -132,13 +132,15 @@ struct VulkanPostVSData
     VkDeviceMemory bufmem;
     VkPrimitiveTopology topo;
 
+    int32_t baseVertex;
+
     uint32_t numVerts;
     uint32_t vertStride;
     uint32_t instStride;
 
     bool useIndices;
-    VkBuffer idxBuf;
-    VkDeviceMemory idxBufMem;
+    ResourceId idxBuf;
+    VkDeviceSize idxOffset;
     VkIndexType idxFmt;
 
     bool hasPosOut;

renderdoc/driver/vulkan/vk_state.cpp

@@ -276,7 +276,7 @@ void VulkanRenderState::BindPipeline(VkCommandBuffer cmd, PipelineBinding bindin
 
     // only set push constant ranges that the layout uses
     for(size_t i = 0; i < pushRanges.size(); i++)
-      ObjDisp(cmd)->CmdPushConstants(Unwrap(cmd), Unwrap(layout), pushRanges[i].stageFlags,
+      ObjDisp(cmd)->CmdPushConstants(Unwrap(cmd), Unwrap(layout), VK_SHADER_STAGE_COMPUTE_BIT,
                                      pushRanges[i].offset, pushRanges[i].size,
                                      pushconsts + pushRanges[i].offset);
 

renderdoc/driver/vulkan/wrappers/vk_descriptor_funcs.cpp

@@ -244,6 +244,17 @@ bool WrappedVulkan::Serialise_vkCreateDescriptorSetLayout(
   {
     VkDescriptorSetLayout layout = VK_NULL_HANDLE;
 
+    VkDescriptorSetLayoutBinding *bindings = (VkDescriptorSetLayoutBinding *)CreateInfo.pBindings;
+
+    // ensure any bindings available to the vertex shader are also available to compute. This is
+    // valid and changes nothing, but means we don't have to create a duplicate parallel 'computer
+    // friendly' descriptor set layout and pipeline layout.
+    for(uint32_t i = 0; i < CreateInfo.bindingCount; i++)
+    {
+      if(bindings[i].stageFlags & VK_SHADER_STAGE_VERTEX_BIT)
+        bindings[i].stageFlags |= VK_SHADER_STAGE_COMPUTE_BIT;
+    }
+
     VkDescriptorSetLayoutCreateInfo unwrapped = UnwrapInfo(&CreateInfo);
     VkResult ret =
         ObjDisp(device)->CreateDescriptorSetLayout(Unwrap(device), &unwrapped, NULL, &layout);

renderdoc/driver/vulkan/wrappers/vk_device_funcs.cpp

@@ -1096,11 +1096,6 @@ bool WrappedVulkan::Serialise_vkCreateDevice(SerialiserType &ser, VkPhysicalDevi
           "robustBufferAccess = false, out of bounds access due to bugs in application or "
           "RenderDoc may cause crashes");
 
-    if(availFeatures.vertexPipelineStoresAndAtomics)
-      enabledFeatures.vertexPipelineStoresAndAtomics = true;
-    else
-      RDCWARN("vertexPipelineStoresAndAtomics = false, output mesh data will not be available");
-
     if(availFeatures.shaderStorageImageWriteWithoutFormat)
       enabledFeatures.shaderStorageImageWriteWithoutFormat = true;
     else