121 lines
4.2 KiB
Markdown
121 lines
4.2 KiB
Markdown
# Ray Query - Tutorial
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## Tutorial ([Setup](../docs/setup.md))
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This is an extension of the Vulkan ray tracing [tutorial](https://nvpro-samples.github.io/vk_raytracing_tutorial_KHR/vkrt_tutorial.md.html).
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This extension is allowing to execute ray intersection queries in any shader stages. In this example, we will add
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ray queries [(GLSL_EXT_ray_query)](https://github.com/KhronosGroup/GLSL/blob/master/extensions/ext/GLSL_EXT_ray_query.txt) to the fragment shader to cast shadow rays.
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In the contrary to all other examples, with this one, we are removing code. There are no need to have a SBT and a raytracing pipeline, the only thing that
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will matter, is the creation of the acceleration structure.
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Starting from the end of the tutorial, [ray_tracing__simple](https://github.com/nvpro-samples/vk_raytracing_tutorial_KHR/tree/master/ray_tracing__simple) we will remove
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all functions that were dedicated to ray tracing and keep only the construction of the BLAS and TLAS.
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## Cleanup
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First, let's remove all extra code
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### hello_vulkan (header)
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Remove most functions and members to keep only what is need to create the acceleration structure:
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~~~~ C++
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// #VKRay
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void initRayTracing();
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auto objectToVkGeometryKHR(const ObjModel& model);
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void createBottomLevelAS();
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void createTopLevelAS();
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VkPhysicalDeviceRayTracingPipelinePropertiesKHR m_rtProperties{VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_RAY_TRACING_PIPELINE_PROPERTIES_KHR};
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nvvk::RaytracingBuilderKHR m_rtBuilder;
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~~~~
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### hello_vulkan (source)
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From the source code, remove the code for all functions that was previously removed.
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### Shaders
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You can safely remove all raytrace.* shaders
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## Support for Fragment shader
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In `HelloVulkan::createDescriptorSetLayout`, add the acceleration structure to the description layout to have access to the acceleration structure directly in the fragment shader.
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~~~~ C++
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// The top level acceleration structure
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m_descSetLayoutBind.addBinding(eTlas, VK_DESCRIPTOR_TYPE_ACCELERATION_STRUCTURE_KHR, 1, VK_SHADER_STAGE_FRAGMENT_BIT);
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~~~~
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But since we will use only one descriptor set, change the binding value or `eTlas` to 3, such that binding will look like this
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~~~~ C++
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eGlobals = 0, // Global uniform containing camera matrices
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eObjDescs = 1, // Access to the object descriptions
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eTextures = 2, // Access to textures
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eTlas = 3 // Top-level acceleration structure
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~~~~
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In `HelloVulkan::updateDescriptorSet`, write the value to the descriptor set.
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~~~~ C++
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VkAccelerationStructureKHR tlas = m_rtBuilder.getAccelerationStructure();
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VkWriteDescriptorSetAccelerationStructureKHR descASInfo{VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET_ACCELERATION_STRUCTURE_KHR};
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descASInfo.accelerationStructureCount = 1;
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descASInfo.pAccelerationStructures = &tlas;
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writes.emplace_back(m_descSetLayoutBind.makeWrite(m_descSet, eTlas, &descASInfo));
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~~~~
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### Shader
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The last modification is in the fragment shader, where we will add the ray intersection query to trace shadow rays.
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First, the version has bumpped to 460
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~~~~ C++
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#version 460
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~~~~
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Then we need to add new extensions
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~~~~ C++
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#extension GL_EXT_ray_tracing : enable
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#extension GL_EXT_ray_query : enable
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~~~~
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We have to add the layout to access the top level acceleration structure.
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~~~~ C++
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layout(binding = eTlas) uniform accelerationStructureEXT topLevelAS;
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~~~~
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At the end of the shader, add the following code to initiate the ray query. As we are only interested to know if the ray
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has hit something, we can keep the minimal.
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~~~~ C++
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// Ray Query for shadow
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vec3 origin = i_worldPos;
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vec3 direction = L; // vector to light
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float tMin = 0.01f;
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float tMax = lightDistance;
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// Initializes a ray query object but does not start traversal
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rayQueryEXT rayQuery;
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rayQueryInitializeEXT(rayQuery, topLevelAS, gl_RayFlagsTerminateOnFirstHitEXT, 0xFF, origin, tMin, direction, tMax);
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// Start traversal: return false if traversal is complete
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while(rayQueryProceedEXT(rayQuery))
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{
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}
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// Returns type of committed (true) intersection
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if(rayQueryGetIntersectionTypeEXT(rayQuery, true) != gl_RayQueryCommittedIntersectionNoneEXT)
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{
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// Got an intersection == Shadow
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o_color *= 0.1;
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}
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~~~~
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