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docs/vkrt_tuto_rayquery.md.htm

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+**NVIDIA Vulkan Ray Tracing Tutorial**
+**Ray Query**
+
+
+![](Images/rayquery.png)
+
+This is an extension of the Vulkan ray tracing [tutorial](vkrt_tutorial.md.htm).
+
+(insert setup.md.html here)
+
+# Ray Query
+
+This extension is allowing to execute ray intersection queries in any shader stages. In this example, we will add 
+ray queries to the fragment shader to cast shadow rays.
+
+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 
+will matter, is the creation of the acceleration structure.
+
+Starting from the end of the tutorial, [ray_tracing__simple](https://github.com/nvpro-samples/vk_raytracing_tutorial/tree/master/ray_tracing__simple) we will remove 
+all functions that were dedicated to ray tracing and keep only the construction of the BLAS and TLAS.
+
+# Cleanup 
+
+First, let's remove all extra code
+
+## hello_vulkan (header)
+
+Remove most functions and members to keep only what is need to create the acceleration structure:
+
+~~~~ C++
+// #VKRay
+void                               initRayTracing();
+nvvkpp::RaytracingBuilderKHR::Blas objectToVkGeometryKHR(const ObjModel& model);
+void                               createBottomLevelAS();
+void                               createTopLevelAS();
+
+vk::PhysicalDeviceRayTracingPropertiesKHR m_rtProperties;
+nvvkpp::RaytracingBuilderKHR              m_rtBuilder;
+~~~~ 
+
+## hello_vulkan (source)
+
+From the source code, remove the code for all functions that was previously removed.
+
+## Shaders
+
+You can safely remove all raytrace.* shaders 
+
+
+# Support for Fragment shader
+
+In `HelloVulkan::createDescriptorSetLayout`, add the acceleration structure to the description layout.
+
+~~~~ C++
+// The top level acceleration structure
+m_descSetLayoutBind.emplace_back(  //
+    vkDS(7, vkDT::eAccelerationStructureKHR, 1, vkSS::eFragment));
+~~~~ 
+
+In `HelloVulkan::updateDescriptorSet`, write the value to the descriptor set.
+
+~~~~ C++
+vk::WriteDescriptorSetAccelerationStructureKHR descASInfo;
+descASInfo.setAccelerationStructureCount(1);
+descASInfo.setPAccelerationStructures(&m_rtBuilder.getAccelerationStructure());
+writes.emplace_back(nvvkpp::util::createWrite(m_descSet, m_descSetLayoutBind[7], &descASInfo));
+~~~~ 
+
+
+## Shader 
+
+The last modification is in the fragment shader, where we will add the ray intersection query to trace shadow rays.
+
+First, the version has bumpped to 460
+
+~~~~ C++
+#version 460
+~~~~ 
+
+Then we need to add new extensions
+
+~~~~ C++
+#extension GL_EXT_ray_tracing : enable
+#extension GL_EXT_ray_query : enable
+~~~~
+
+We have to add the layout to access the top level acceleration structure.
+
+~~~~ C++
+layout(binding = 7, set = 0) uniform accelerationStructureEXT topLevelAS;
+~~~~
+
+
+Ad the end of the shader, add the following code to initiate the ray query. As we are only interested to know if the ray 
+has hit something, we can keep the minimal.
+
+~~~~ C++
+// Ray Query for shadow
+vec3  origin    = worldPos;
+vec3  direction = L;  // vector to light
+float tMin      = 0.01f;
+float tMax      = lightDistance;
+
+// Initializes a ray query object but does not start traversal
+rayQueryEXT rayQuery;
+rayQueryInitializeEXT(rayQuery, topLevelAS, gl_RayFlagsTerminateOnFirstHitEXT, 0xFF, origin, tMin,
+                      direction, tMax);
+
+// Start traversal: return false if traversal is complete
+while(rayQueryProceedEXT(rayQuery))
+{
+}
+
+// Returns type of committed (true) intersection
+if(rayQueryGetIntersectionTypeEXT(rayQuery, true) != gl_RayQueryCommittedIntersectionNoneEXT)
+{
+  // Got an intersection == Shadow
+  outColor *= 0.1;
+}
+~~~~
+
+
+
+
+
+
+
+
+
+!!! Info Ray Query
+    Information about [Ray Query](https://github.com/KhronosGroup/GLSL/blob/master/extensions/ext/GLSL_EXT_ray_query.txt) extension.
+
+# Final Code 
+
+You can find the final code in the folder [ray_tracing_reflections](https://github.com/nvpro-samples/vk_raytracing_tutorial/tree/master/ray_tracing_reflections)
+
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