ERROR: VUID-vkCmdBuildAccelerationStructuresKHR-geometry-03673 --> Validation Error: [ VUID-vkCmdBuildAccelerationStructuresKHR-geometry-03673 ] Object 0: handle = 0x19a7cf724f0, type = VK_OBJECT_TYPE_DEVICE; Object 1: handle = 0xd5b26f0000000010, type = VK_OBJECT_TYPE_BUFFER; | MessageID = 0x8a7de95d | vkCmdBuildAccelerationStructuresKHR(): The buffer associated with pInfos[0].pGeometries[0].geometry.instances.data was not created with VK_BUFFER_USAGE_ACCELERATION_STRUCTURE_BUILD_INPUT_READ_ONLY_BIT_KHR. The Vulkan spec states: The buffers from which the buffer device addresses for all of the geometry.triangles.vertexData, geometry.triangles.indexData, geometry.triangles.transformData, geometry.aabbs.data, and geometry.instances.data members of all pInfos[i].pGeometries and pInfos[i].ppGeometries are queried must have been created with the VK_BUFFER_USAGE_ACCELERATION_STRUCTURE_BUILD_INPUT_READ_ONLY_BIT_KHR usage flag (https://vulkan.lunarg.com/doc/view/1.3.216.0/windows/1.3-extensions/vkspec.html

Listing 4-1, is:

vec3 tmpu = P - A, tmpv = P - B, tmpw = P - C // ... vec3 Pp = P + u*tmpu + v*tmpv + w*tmpw

As source Spectral light transport simulation using a precision-based ray tracing architecture is quoted. Here, the last line looks like this (adjusting for code style):

vec3 Pp = u*(A + tmpu) + v*(B + tmpv) + w*(C + tmpw)

I don´t think they are equivalent, and the first version gives me unexpected results. Is this a mistake?

I'm studing Vulkan Raytracing. While reading "Ray Tracing Gems II", I found a mistake.

In Chapter 16 "INTRODUCTION TO VULKAN RAY TRACING", I seem to it needed "VK_BUFFER_USAGE_ACCELERATION_STRUCTURE_BUILD_INPUT_READ_ONLY_BIT_KHR". (at List 16-18)

i use Vulkan SDK version 1.2.182.0.

@acmarrs-nvidia Hey Adam! In Chapter 23, Figure 23-4, the code as listed looks like the following:

function updateReservoir(Reservoir result, Reservoir input)
    result.totalWeight+= input.weight;
    result.M++;
    if rand() < (input.weight/result.totalWeight) then
        result.sample = input.sample;
        result.sampleTargetPdf = input.sampleTargetPdf;
    return result;

function mergeReservoirs(Reservoir r1, Reservoir r2)
    Reservoir merged;
    updateReservoir(merged, r1);
    updateReservoir(merged, r2);
    merged.M = r1.M + r2.M;
    return merged;

As written, this code works but I believe updateReservoir has a bug in it, specifically related to the update of result.M (which denotes the sample count). I believe the correct update should be result.M += input.M;. Note that the listing as a whole works provided the user only uses mergeReservoirs because merged.M is overwritten with the correct result afterwards. A refactored code listing might look like:

function updateReservoir(Reservoir result, Reservoir input)
    result.totalWeight+= input.weight;
    result.M += input.M;
    if rand() < (input.weight/result.totalWeight) then
        result.sample = input.sample;
        result.sampleTargetPdf = input.sampleTargetPdf;
    return result;

function mergeReservoirs(Reservoir r1, Reservoir r2)
    Reservoir merged = r1;
    updateReservoir(merged, r2);
    return merged;

Note: the only distinction between mergeReservoirs and updateReservoir as implemented above is that the former leaves its arguments r1 and r2 unchanged, while updateReservoir mutates the first argument.