601 lines
22 KiB
Markdown
601 lines
22 KiB
Markdown
# NVIDIA Vulkan Ray Tracing Tutorial - glTF Scene
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This example is the result of the modification of the [simple ray tracing](../ray_tracing__simple) tutorial.
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Instead of loading separated OBJ objects, the example was modified to load glTF scene files containing multiple objects.
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This example is not about shading, but using more complex data than OBJ.
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For a more complete version, see
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* https://github.com/nvpro-samples/vk_raytrace
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* https://github.com/nvpro-samples/vk_shaded_gltfscene
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## Scene Data
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The OBJ models were loaded and stored in four buffers:
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* vertices: array of structure of position, normal, texcoord, color
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* indices: index of the vertex, every three makes a triangle
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* materials: the wavefront material structure
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* material index: material index per triangle.
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Since we could have multiple OBJ, we would have arrays of those buffers.
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With glTF scene, the data will be organized differently a choice we have made for convenience. Instead of having structure of vertices,
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positions, normals and other attributes will be in separate buffers. There will be one single position buffer,
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for all geometries of the scene, same for indices and other attributes. But for each geometry there is the information
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of the number of elements and offsets.
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From the source tutorial, we will not need the following and therefore remove it:
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~~~~C
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std::vector<ObjModel> m_objModel; // Model on host
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std::vector<ObjDesc> m_objDesc; // Model description for device access
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std::vector<ObjInstance> m_instances; // Scene model instances
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~~~~
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In `host_device.h` we will add new host/device structures: PrimMeshInfo, SceneDesc and GltfShadeMaterial.
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~~~~C
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// Structure used for retrieving the primitive information in the closest hit
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struct PrimMeshInfo
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{
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uint indexOffset;
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uint vertexOffset;
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int materialIndex;
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};
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// Scene buffer addresses
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struct SceneDesc
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{
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uint64_t vertexAddress; // Address of the Vertex buffer
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uint64_t normalAddress; // Address of the Normal buffer
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uint64_t uvAddress; // Address of the texture coordinates buffer
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uint64_t indexAddress; // Address of the triangle indices buffer
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uint64_t materialAddress; // Address of the Materials buffer (GltfShadeMaterial)
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uint64_t primInfoAddress; // Address of the mesh primitives buffer (PrimMeshInfo)
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};
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~~~~
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And also, our glTF material representation for the shading. This is a stripped down version of the glTF PBR. If you are interested in the
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correct PBR implementation, check out [vk_raytrace](https://github.com/nvpro-samples/vk_raytrace).
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~~~~ C
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struct GltfShadeMaterial
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{
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vec4 pbrBaseColorFactor;
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vec3 emissiveFactor;
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int pbrBaseColorTexture;
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};
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~~~~
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And for holding the all the buffers allocated for representing the scene, we will store them in the following.
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~~~~C
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nvh::GltfScene m_gltfScene;
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nvvk::Buffer m_vertexBuffer;
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nvvk::Buffer m_normalBuffer;
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nvvk::Buffer m_uvBuffer;
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nvvk::Buffer m_indexBuffer;
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nvvk::Buffer m_materialBuffer;
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nvvk::Buffer m_primInfo;
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nvvk::Buffer m_sceneDesc;
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~~~~
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## Loading glTF scene
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To load the scene, we will be using [TinyGLTF](https://github.com/syoyo/tinygltf) from Syoyo Fujita, then to avoid traversing
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the scene graph, the information will be flatten using the helper [gltfScene](https://github.com/nvpro-samples/nvpro_core/tree/master/nvh#gltfscenehpp).
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### Loading Scene
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Instead of loading a model, we will be loading a scene, so we are replacing `loadModel()` by `loadScene()`.
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In the source file, loading the scene `loadScene()` will have first the glTF import with TinyGLTF.
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~~~~C
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tinygltf::Model tmodel;
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tinygltf::TinyGLTF tcontext;
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std::string warn, error;
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if(!tcontext.LoadASCIIFromFile(&tmodel, &error, &warn, filename))
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assert(!"Error while loading scene");
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~~~~
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Then we will flatten the scene graph and grab the information we will need using the gltfScene helper.
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~~~~C
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m_gltfScene.importMaterials(tmodel);
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m_gltfScene.importDrawableNodes(tmodel,
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nvh::GltfAttributes::Normal | nvh::GltfAttributes::Texcoord_0);
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~~~~
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The next part is to allocate the buffers to hold the information, such as the positions, normals, texture coordinates, etc.
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~~~~C
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// Create the buffers on Device and copy vertices, indices and materials
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nvvk::CommandPool cmdBufGet(m_device, m_graphicsQueueIndex);
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VkCommandBuffer cmdBuf = cmdBufGet.createCommandBuffer();
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m_vertexBuffer = m_alloc.createBuffer(cmdBuf, m_gltfScene.m_positions,
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VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_STORAGE_BUFFER_BIT | VK_BUFFER_USAGE_SHADER_DEVICE_ADDRESS_BIT
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| VK_BUFFER_USAGE_ACCELERATION_STRUCTURE_BUILD_INPUT_READ_ONLY_BIT_KHR);
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m_indexBuffer = m_alloc.createBuffer(cmdBuf, m_gltfScene.m_indices,
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VK_BUFFER_USAGE_INDEX_BUFFER_BIT | VK_BUFFER_USAGE_STORAGE_BUFFER_BIT | VK_BUFFER_USAGE_SHADER_DEVICE_ADDRESS_BIT
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| VK_BUFFER_USAGE_ACCELERATION_STRUCTURE_BUILD_INPUT_READ_ONLY_BIT_KHR);
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m_normalBuffer = m_alloc.createBuffer(cmdBuf, m_gltfScene.m_normals,
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VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_STORAGE_BUFFER_BIT
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| VK_BUFFER_USAGE_SHADER_DEVICE_ADDRESS_BIT);
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m_uvBuffer = m_alloc.createBuffer(cmdBuf, m_gltfScene.m_texcoords0,
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VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_STORAGE_BUFFER_BIT
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| VK_BUFFER_USAGE_SHADER_DEVICE_ADDRESS_BIT);
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~~~~
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We are making a simple material, extracting only a few members from the glTF material.
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~~~~ C++
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// Copying all materials, only the elements we need
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std::vector<GltfShadeMaterial> shadeMaterials;
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for(auto& m : m_gltfScene.m_materials)
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{
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shadeMaterials.emplace_back(GltfShadeMaterial{m.baseColorFactor, m.emissiveFactor, m.baseColorTexture});
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}
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m_materialBuffer = m_alloc.createBuffer(cmdBuf, shadeMaterials,
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VK_BUFFER_USAGE_STORAGE_BUFFER_BIT | VK_BUFFER_USAGE_SHADER_DEVICE_ADDRESS_BIT);
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~~~~
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To find the positions of the triangle hit in the closest hit shader, as well as the other
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attributes, we will store the offsets information of that geometry.
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~~~~C
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// The following is used to find the primitive mesh information in the CHIT
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std::vector<PrimMeshInfo> primLookup;
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for(auto& primMesh : m_gltfScene.m_primMeshes)
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{
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primLookup.push_back({primMesh.firstIndex, primMesh.vertexOffset, primMesh.materialIndex});
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}
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m_rtPrimLookup =
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m_alloc.createBuffer(cmdBuf, primLookup, VK_BUFFER_USAGE_STORAGE_BUFFER_BIT | VK_BUFFER_USAGE_SHADER_DEVICE_ADDRESS_BIT);
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~~~~
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Finally, we are creating a buffer holding the address of all buffers
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~~~~ C++
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SceneDesc sceneDesc;
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sceneDesc.vertexAddress = nvvk::getBufferDeviceAddress(m_device, m_vertexBuffer.buffer);
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sceneDesc.indexAddress = nvvk::getBufferDeviceAddress(m_device, m_indexBuffer.buffer);
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sceneDesc.normalAddress = nvvk::getBufferDeviceAddress(m_device, m_normalBuffer.buffer);
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sceneDesc.uvAddress = nvvk::getBufferDeviceAddress(m_device, m_uvBuffer.buffer);
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sceneDesc.materialAddress = nvvk::getBufferDeviceAddress(m_device, m_materialBuffer.buffer);
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sceneDesc.primInfoAddress = nvvk::getBufferDeviceAddress(m_device, m_primInfo.buffer);
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m_sceneDesc = m_alloc.createBuffer(cmdBuf, sizeof(SceneDesc), &sceneDesc,
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VK_BUFFER_USAGE_STORAGE_BUFFER_BIT | VK_BUFFER_USAGE_SHADER_DEVICE_ADDRESS_BIT);
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~~~~
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Before closing the function, we will create textures (none in default scene) and submitting the command buffer.
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The finalize and releasing staging is waiting for the copy of all data to the GPU.
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~~~~ C
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// Creates all textures found
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createTextureImages(cmdBuf, tmodel);
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cmdBufGet.submitAndWait(cmdBuf);
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m_alloc.finalizeAndReleaseStaging();
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NAME_VK(m_vertexBuffer.buffer);
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NAME_VK(m_indexBuffer.buffer);
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NAME_VK(m_normalBuffer.buffer);
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NAME_VK(m_uvBuffer.buffer);
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NAME_VK(m_materialBuffer.buffer);
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NAME_VK(m_primInfo.buffer);
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NAME_VK(m_sceneDesc.buffer);
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}
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~~~~
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**:warning: NOTE**: the macro `NAME_VK` is a convenience to name Vulkan object to easily identify them in Nsight Graphics and to know where it was created.
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## Converting geometry to BLAS
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Instead of `objectToVkGeometryKHR()`, we will be using `primitiveToVkGeometry(const nvh::GltfPrimMesh& prim)`.
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The function is similar, only the input is different, except for `VkAccelerationStructureBuildRangeInfoKHR` where
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we also include the offsets.
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~~~~C
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//--------------------------------------------------------------------------------------------------
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// Converting a GLTF primitive in the Raytracing Geometry used for the BLAS
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//
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auto HelloVulkan::primitiveToGeometry(const nvh::GltfPrimMesh& prim)
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{
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// BLAS builder requires raw device addresses.
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VkDeviceAddress vertexAddress = nvvk::getBufferDeviceAddress(m_device, m_vertexBuffer.buffer);
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VkDeviceAddress indexAddress = nvvk::getBufferDeviceAddress(m_device, m_indexBuffer.buffer);
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uint32_t maxPrimitiveCount = prim.indexCount / 3;
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// Describe buffer as array of VertexObj.
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VkAccelerationStructureGeometryTrianglesDataKHR triangles{VK_STRUCTURE_TYPE_ACCELERATION_STRUCTURE_GEOMETRY_TRIANGLES_DATA_KHR};
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triangles.vertexFormat = VK_FORMAT_R32G32B32_SFLOAT; // vec3 vertex position data.
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triangles.vertexData.deviceAddress = vertexAddress;
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triangles.vertexStride = sizeof(glm::vec3);
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// Describe index data (32-bit unsigned int)
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triangles.indexType = VK_INDEX_TYPE_UINT32;
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triangles.indexData.deviceAddress = indexAddress;
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// Indicate identity transform by setting transformData to null device pointer.
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//triangles.transformData = {};
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triangles.maxVertex = prim.vertexCount - 1;
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// Identify the above data as containing opaque triangles.
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VkAccelerationStructureGeometryKHR asGeom{VK_STRUCTURE_TYPE_ACCELERATION_STRUCTURE_GEOMETRY_KHR};
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asGeom.geometryType = VK_GEOMETRY_TYPE_TRIANGLES_KHR;
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asGeom.flags = VK_GEOMETRY_NO_DUPLICATE_ANY_HIT_INVOCATION_BIT_KHR; // For AnyHit
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asGeom.geometry.triangles = triangles;
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VkAccelerationStructureBuildRangeInfoKHR offset;
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offset.firstVertex = prim.vertexOffset;
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offset.primitiveCount = prim.indexCount / 3;
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offset.primitiveOffset = prim.firstIndex * sizeof(uint32_t);
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offset.transformOffset = 0;
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// Our blas is made from only one geometry, but could be made of many geometries
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nvvk::RaytracingBuilderKHR::BlasInput input;
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input.asGeometry.emplace_back(asGeom);
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input.asBuildOffsetInfo.emplace_back(offset);
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return input;
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}
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~~~~
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## Top Level creation
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There are almost no differences, besides the fact that the index of the geometry is stored in `primMesh`.
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~~~~C
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for(auto& node : m_gltfScene.m_nodes)
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{
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VkAccelerationStructureInstanceKHR rayInst;
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rayInst.transform = nvvk::toTransformMatrixKHR(node.worldMatrix);
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rayInst.instanceCustomIndex = node.primMesh; // gl_InstanceCustomIndexEXT: to find which primitive
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rayInst.accelerationStructureReference = m_rtBuilder.getBlasDeviceAddress(node.primMesh);
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rayInst.flags = VK_GEOMETRY_INSTANCE_TRIANGLE_FACING_CULL_DISABLE_BIT_KHR;
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rayInst.mask = 0xFF;
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rayInst.instanceShaderBindingTableRecordOffset = 0; // We will use the same hit group for all objects
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tlas.emplace_back(rayInst);
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}
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~~~~
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## Raster Rendering
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Raster rendering is simple. The shader was changed to use vertex, normal and texture coordinates. For
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each node, we will be pushing the material Id this primitive is using. Since we have flatten the scene graph,
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we can loop over all drawable nodes.
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~~~~C
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std::vector<VkBuffer> vertexBuffers = {m_vertexBuffer.buffer, m_normalBuffer.buffer, m_uvBuffer.buffer};
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vkCmdBindVertexBuffers(cmdBuf, 0, static_cast<uint32_t>(vertexBuffers.size()), vertexBuffers.data(), offsets.data());
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vkCmdBindIndexBuffer(cmdBuf, m_indexBuffer.buffer, 0, VK_INDEX_TYPE_UINT32);
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uint32_t idxNode = 0;
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for(auto& node : m_gltfScene.m_nodes)
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{
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auto& primitive = m_gltfScene.m_primMeshes[node.primMesh];
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m_pcRaster.modelMatrix = node.worldMatrix;
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m_pcRaster.objIndex = node.primMesh;
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m_pcRaster.materialId = primitive.materialIndex;
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vkCmdPushConstants(cmdBuf, m_pipelineLayout, VK_SHADER_STAGE_VERTEX_BIT | VK_SHADER_STAGE_FRAGMENT_BIT, 0,
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sizeof(PushConstantRaster), &m_pcRaster);
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vkCmdDrawIndexed(cmdBuf, primitive.indexCount, 1, primitive.firstIndex, primitive.vertexOffset, 0);
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}
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~~~~
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## Ray tracing change
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In `createRtDescriptorSet()`, the only change we will add is the primitive info buffer to retrieve
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the data when hitting a triangle.
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~~~~C
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m_rtDescSetLayoutBind.addBinding(ePrimLookup, VK_DESCRIPTOR_TYPE_STORAGE_BUFFER, 1,
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VK_SHADER_STAGE_CLOSEST_HIT_BIT_KHR | VK_SHADER_STAGE_ANY_HIT_BIT_KHR); // Primitive info
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// ...
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VkDescriptorBufferInfo primitiveInfoDesc{m_rtPrimLookup.buffer, 0, VK_WHOLE_SIZE};
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// ...
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writes.emplace_back(m_rtDescSetLayoutBind.makeWrite(m_rtDescSet, ePrimLookup, &primitiveInfoDesc));
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~~~~
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## Descriptors and Pipeline Changes
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Since we are using different buffers and the vertex is no longer a struct but is using
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3 different buffers for the position, normal and texture coord.
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The methods `createDescriptorSetLayout()`, `updateDescriptorSet()` and `createGraphicsPipeline()`
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will be changed accordingly.
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See [hello_vulkan](hello_vulkan.cpp)
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## Shaders
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The shading is the same and is not reflecting the glTF PBR shading model, but the shaders were nevertheless
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changed to fit the new incoming format.
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* Raster : [vertex](shaders/vert_shader.vert), [fragment](shaders/frag_shader.frag)
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* Ray Trace: [RayGen](shaders/raytrace.rgen), [ClosestHit](shaders/raytrace.rchit)
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## Other changes
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Small other changes were done, a different scene, different camera and light position.
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Camera position
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~~~~C
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CameraManip.setLookat(glm::vec3(0, 0, 15), glm::vec3(0, 0, 0), glm::vec3(0, 1, 0));
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~~~~
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Scene
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~~~~C
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helloVk.loadScene(nvh::findFile("media/scenes/cornellBox.gltf", defaultSearchPaths, true));
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~~~~
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Light Position
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~~~~C
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glm::vec3 lightPosition{0.f, 4.5f, 0.f};
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~~~~
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# Simple Path Tracing
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To convert this example to a simple path tracer (see Wikipedia [Path Tracing](https://en.wikipedia.org/wiki/Path_tracing)), we need to change the `RayGen` and the `ClosestHit` shaders.
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Before doing this, we will modify the application to send the current rendering frame, allowing to accumulate
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samples.
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Add the following two functions in `hello_vulkan.cpp`:
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~~~~C
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//--------------------------------------------------------------------------------------------------
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// If the camera matrix has changed, resets the frame.
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// otherwise, increments frame.
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//
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void HelloVulkan::updateFrame()
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{
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static glm::mat4 refCamMatrix;
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static float refFov{CameraManip.getFov()};
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const auto& m = CameraManip.getMatrix();
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const auto fov = CameraManip.getFov();
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if(refCamMatrix != m || refFov != fov)
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{
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resetFrame();
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refCamMatrix = m;
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refFov = fov;
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}
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m_pcRay.frame++;
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}
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void HelloVulkan::resetFrame()
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{
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m_pcRay.frame = -1;
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}
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~~~~
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And call `updateFrame()` in the begining of the `raytrace()` function.
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In `hello_vulkan.cpp`, add the function declarations
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~~~~C
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void updateFrame();
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void resetFrame();
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~~~~
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And add a new `frame` member at the end of `RtPushConstant` structure.
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## Ray Generation
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There are a few modifications to be done in the ray generation. First, it will use the clock for its random seed number.
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This is done by adding the [`GL_ARB_shader_clock`](https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_shader_clock.txt) extension.
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~~~~C
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#extension GL_ARB_shader_clock : enable
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~~~~
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The random number generator is in `sampling.glsl`, `#include` this file.
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In `main()`, we will initialize the random number like this: (see tutorial on jitter camera)
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~~~~C
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// Initialize the random number
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uint seed = tea(gl_LaunchIDEXT.y * gl_LaunchSizeEXT.x + gl_LaunchIDEXT.x, int(clockARB()));
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~~~~
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To accumulate the samples, instead of only write to the image, we will also use the previous frame.
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~~~~C
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// Do accumulation over time
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if(pcRay.frame > 0)
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{
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float a = 1.0f / float(pcRay.frame + 1);
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vec3 old_color = imageLoad(image, ivec2(gl_LaunchIDEXT.xy)).xyz;
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imageStore(image, ivec2(gl_LaunchIDEXT.xy), vec4(mix(old_color, hitValue, a), 1.f));
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}
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else
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{
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// First frame, replace the value in the buffer
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imageStore(image, ivec2(gl_LaunchIDEXT.xy), vec4(hitValue, 1.f));
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}
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~~~~
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Extra information will be needed in the ray payload `hitPayload`, the `seed` and the `depth`.
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The modification in `raycommon.glsl`
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~~~~C
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struct hitPayload
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{
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vec3 hitValue;
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uint seed;
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uint depth;
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};
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~~~~
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## Closest Hit Shader
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This modification will recursively trace until the `depth`hits 10 (hardcoded) or hit an emissive element (light).
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The only information that we will keep from the shader, is the calculation of the hit state: the position and normal. So
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all code from `// Vector toward the light` to the end can be removed and be replaced by the following.
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~~~~C
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// https://en.wikipedia.org/wiki/Path_tracing
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// Material of the object
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GltfMaterial mat = materials[nonuniformEXT(matIndex)];
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vec3 emittance = mat.emissiveFactor;
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// Pick a random direction from here and keep going.
|
|
vec3 tangent, bitangent;
|
|
createCoordinateSystem(world_normal, tangent, bitangent);
|
|
vec3 rayOrigin = world_position;
|
|
vec3 rayDirection = samplingHemisphere(prd.seed, tangent, bitangent, world_normal);
|
|
|
|
const float cos_theta = dot(rayDirection, world_normal);
|
|
// Probability density function of samplingHemisphere choosing this rayDirection
|
|
const float p = cos_theta / M_PI;
|
|
|
|
// Compute the BRDF for this ray (assuming Lambertian reflection)
|
|
vec3 albedo = mat.pbrBaseColorFactor.xyz;
|
|
if(mat.pbrBaseColorTexture > -1)
|
|
{
|
|
uint txtId = mat.pbrBaseColorTexture;
|
|
albedo *= texture(texturesMap[nonuniformEXT(txtId)], texcoord0).xyz;
|
|
}
|
|
vec3 BRDF = albedo / M_PI;
|
|
|
|
// Recursively trace reflected light sources.
|
|
if(prd.depth < 10)
|
|
{
|
|
prd.depth++;
|
|
float tMin = 0.001;
|
|
float tMax = 100000000.0;
|
|
uint flags = gl_RayFlagsOpaqueEXT;
|
|
traceRayEXT(topLevelAS, // acceleration structure
|
|
flags, // rayFlags
|
|
0xFF, // cullMask
|
|
0, // sbtRecordOffset
|
|
0, // sbtRecordStride
|
|
0, // missIndex
|
|
rayOrigin, // ray origin
|
|
tMin, // ray min range
|
|
rayDirection, // ray direction
|
|
tMax, // ray max range
|
|
0 // payload (location = 0)
|
|
);
|
|
}
|
|
vec3 incoming = prd.hitValue;
|
|
|
|
// Apply the Rendering Equation here.
|
|
prd.hitValue = emittance + (BRDF * incoming * cos_theta / p);
|
|
~~~~
|
|
|
|
:warning: **Note:** We do not implement the point light as in the Rasterizer. Therefore, only the emitting geometry will emit the energy to illuminate the scene.
|
|
|
|
## Miss Shader
|
|
|
|
To avoid contribution from the environment.
|
|
|
|
~~~~C
|
|
void main()
|
|
{
|
|
if(prd.depth == 0)
|
|
prd.hitValue = clearColor.xyz * 0.8;
|
|
else
|
|
prd.hitValue = vec3(0.01); // Tiny contribution from environment
|
|
prd.depth = 100; // Ending trace
|
|
}
|
|
~~~~
|
|
|
|
# Faster Path Tracer
|
|
|
|
The implementation above is recursive and this is really not optimal. As described in the [reflection](../ray_tracing_reflections)
|
|
tutorial, the best is to break the recursivity and do most of the work in the `RayGen`.
|
|
|
|
The following change can give up to **3 time faster** rendering.
|
|
|
|
To be able to do this, we need to extend the ray `payload` to bring data from the `Closest Hit` to the `RayGen`, which is the
|
|
ray origin and direction and the BRDF weight.
|
|
|
|
~~~~C
|
|
struct hitPayload
|
|
{
|
|
vec3 hitValue;
|
|
uint seed;
|
|
uint depth;
|
|
vec3 rayOrigin;
|
|
vec3 rayDirection;
|
|
vec3 weight;
|
|
};
|
|
~~~~
|
|
|
|
## Closest Hit
|
|
|
|
We don't need to trace anymore, so before tracing a new ray, we can store the information in
|
|
the `payload` and return before the recursion code.
|
|
|
|
~~~~C
|
|
prd.rayOrigin = rayOrigin;
|
|
prd.rayDirection = rayDirection;
|
|
prd.hitValue = emittance;
|
|
prd.weight = BRDF * cos_theta / p;
|
|
return;
|
|
~~~~
|
|
|
|
## Ray Generation
|
|
|
|
The ray generation is the one that will do the trace loop.
|
|
|
|
First initialize the `payload` and variable to compute the accumulation.
|
|
|
|
~~~~C
|
|
prd.rayOrigin = origin.xyz;
|
|
prd.rayDirection = direction.xyz;
|
|
prd.weight = vec3(0);
|
|
|
|
vec3 curWeight = vec3(1);
|
|
vec3 hitValue = vec3(0);
|
|
~~~~
|
|
|
|
Now the loop over the trace function, will be like the following.
|
|
|
|
:warning: **Note:** the depth is hardcode, but could be a parameter to the `push constant`.
|
|
|
|
~~~~C
|
|
for(; prd.depth < 10; prd.depth++)
|
|
{
|
|
traceRayEXT(topLevelAS, // acceleration structure
|
|
rayFlags, // rayFlags
|
|
0xFF, // cullMask
|
|
0, // sbtRecordOffset
|
|
0, // sbtRecordStride
|
|
0, // missIndex
|
|
prd.rayOrigin, // ray origin
|
|
tMin, // ray min range
|
|
prd.rayDirection, // ray direction
|
|
tMax, // ray max range
|
|
0 // payload (location = 0)
|
|
);
|
|
|
|
hitValue += prd.hitValue * curWeight;
|
|
curWeight *= prd.weight;
|
|
}
|
|
~~~~
|
|
|
|
:warning: **Note:** do not forget to use `hitValue` in the `imageStore`.
|