计算着色器浮点算法确实不准确。

Question

我目前正在编写一个计算着色器，它需要一个浮点数和一个uint3的简单浮点乘法，而且我得到的结果非常不准确。

例如，uint3(1，2，3) * 0.25

预期结果: uint3(0.25，0.5，0.75)

实际结果: uint3(0.3，0.5，0.8)

知道怎么提高精度吗？

计算机着色器：

[numthreads(X_THREADS, Y_THREADS, Z_THREADS)]
void CSMain (uint3 id : SV_DispatchThreadID)
{
    // Fill the array
    uint tid = id.x;
    while (tid < octree_length)
    {
        // Normalize tid
        uint depth = OctreeDepth(tid);
        uint mid = tid - depth_offsets[depth];

        // Compute node data
        float node_size = bounds_size / pow(2, depth);
        float3 node_min = MortonToXYZ(mid) * node_size; 

        // Build node
        octree[tid].anchor = node_min;
        octree[tid].size = node_size;

        // Move tid
        tid += total_num_threads;
    }
}

不准确的乘法：

float3 node_min = MortonToXYZ(mid) * node_size; 

thread

• MortonToXYZ:的
• mid:该的Morton代码返回元素介于0，无穷大之间的uint3，这是解码的Morton code
  • node_size：，在0之间浮动，在无穷大

  之间。

启动着色器并将数据读取回的代码：

ComputeBuffer BuildOctree(Vector3 boundsMin, float boundsSize, int octreeDepth, Vector3Int numThreadGroups) 
{
    // Compute constants
    int totalNumThreads = numThreadGroups.x * numThreadGroups.y * numThreadGroups.z * THREADS_PER_GROUPS;

    // Compute depth offsets and octree length
    int[] depthOffsets = new int[octreeDepth];
    int length = 0;

    for (int i = 0; i < octreeDepth; i++)
    {
        depthOffsets[i] = length;
        length += (int) Mathf.Pow(8, i);
    }

    // Prepare buffers
    ComputeBuffer octree = new ComputeBuffer(length, 4 * sizeof(float), ComputeBufferType.Structured);
    ComputeBuffer depthOffsetsGPU = new ComputeBuffer(octreeDepth, sizeof(int), ComputeBufferType.Structured);

    depthOffsetsGPU.SetData(depthOffsets);
    octree.SetData(new OctreeNode[length]);

    // Load data into shader
    OCTREE_BUILDER.SetBuffer(0, "octree", octree);
    OCTREE_BUILDER.SetBuffer(0, "depth_offsets", depthOffsetsGPU);
    OCTREE_BUILDER.SetInt("total_num_threads", totalNumThreads);
    OCTREE_BUILDER.SetInt("octree_length", length);
    OCTREE_BUILDER.SetFloat("bounds_size", boundsSize);

    // Launch kernal
    OCTREE_BUILDER.Dispatch(0, numThreadGroups.x, numThreadGroups.y, numThreadGroups.z);

    OctreeNode[] output = new OctreeNode[length];
    octree.GetData(output);

    for (int i = 0; i < output.Length; i++)
        Debug.Log("cell[" + i + "]: " + output[i].anchor + ", " + output[i].size);

    // Return octree buffer
    return octree;
}

注：\

• I尝试了一个只计算uint3(1，1，1) * 0.25的最小示例

预期结果: uint3(0.25，0.25，0.25)

实际结果: uint3(0.3，0.3，0.3)\

• I正在使用RTX 2070

Answer 1

正如user @bart指出的，问题在打印中，统一打印2位格式，舍入我的值，使用ToString("F5")在我的打印中显示正确的值