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#include "common.h"

///////////////////////////////////////////////////////////////////////////////
/// \brief compute image derivatives
///
/// CUDA kernel, relies heavily on texture unit
/// \param[in]  width   image width
/// \param[in]  height  image height
/// \param[in]  stride  image stride
/// \param[out] Ix      x derivative
/// \param[out] Iy      y derivative
/// \param[out] Iz      temporal derivative
///////////////////////////////////////////////////////////////////////////////
__global__ void ComputeDerivativesKernel(int                 width,
                                         int                 height,
                                         int                 stride,
                                         float              *Ix,
                                         float              *Iy,
                                         float              *Iz,
                                         cudaTextureObject_t texSource,
                                         cudaTextureObject_t texTarget)
{
    const int ix = threadIdx.x + blockIdx.x * blockDim.x;
    const int iy = threadIdx.y + blockIdx.y * blockDim.y;

    const int pos = ix + iy * stride;

    if (ix >= width || iy >= height)
        return;

    float dx = 1.0f / (float)width;
    float dy = 1.0f / (float)height;

    float x = ((float)ix + 0.5f) * dx;
    float y = ((float)iy + 0.5f) * dy;

    float t0, t1;
    // x derivative
    t0 = tex2D<float>(texSource, x - 2.0f * dx, y);
    t0 -= tex2D<float>(texSource, x - 1.0f * dx, y) * 8.0f;
    t0 += tex2D<float>(texSource, x + 1.0f * dx, y) * 8.0f;
    t0 -= tex2D<float>(texSource, x + 2.0f * dx, y);
    t0 /= 12.0f;

    t1 = tex2D<float>(texTarget, x - 2.0f * dx, y);
    t1 -= tex2D<float>(texTarget, x - 1.0f * dx, y) * 8.0f;
    t1 += tex2D<float>(texTarget, x + 1.0f * dx, y) * 8.0f;
    t1 -= tex2D<float>(texTarget, x + 2.0f * dx, y);
    t1 /= 12.0f;

    Ix[pos] = (t0 + t1) * 0.5f;

    // t derivative
    Iz[pos] = tex2D<float>(texTarget, x, y) - tex2D<float>(texSource, x, y);

    // y derivative
    t0 = tex2D<float>(texSource, x, y - 2.0f * dy);
    t0 -= tex2D<float>(texSource, x, y - 1.0f * dy) * 8.0f;
    t0 += tex2D<float>(texSource, x, y + 1.0f * dy) * 8.0f;
    t0 -= tex2D<float>(texSource, x, y + 2.0f * dy);
    t0 /= 12.0f;

    t1 = tex2D<float>(texTarget, x, y - 2.0f * dy);
    t1 -= tex2D<float>(texTarget, x, y - 1.0f * dy) * 8.0f;
    t1 += tex2D<float>(texTarget, x, y + 1.0f * dy) * 8.0f;
    t1 -= tex2D<float>(texTarget, x, y + 2.0f * dy);
    t1 /= 12.0f;

    Iy[pos] = (t0 + t1) * 0.5f;
}

///////////////////////////////////////////////////////////////////////////////
/// \brief compute image derivatives
///
/// \param[in]  I0  source image
/// \param[in]  I1  tracked image
/// \param[in]  w   image width
/// \param[in]  h   image height
/// \param[in]  s   image stride
/// \param[out] Ix  x derivative
/// \param[out] Iy  y derivative
/// \param[out] Iz  temporal derivative
///////////////////////////////////////////////////////////////////////////////
static void ComputeDerivatives(const float *I0, const float *I1, int w, int h, int s, float *Ix, float *Iy, float *Iz)
{
    dim3 threads(32, 6);
    dim3 blocks(iDivUp(w, threads.x), iDivUp(h, threads.y));

    cudaTextureObject_t texSource, texTarget;
    cudaResourceDesc    texRes;
    memset(&texRes, 0, sizeof(cudaResourceDesc));

    texRes.resType                  = cudaResourceTypePitch2D;
    texRes.res.pitch2D.devPtr       = (void *)I0;
    texRes.res.pitch2D.desc         = cudaCreateChannelDesc<float>();
    texRes.res.pitch2D.width        = w;
    texRes.res.pitch2D.height       = h;
    texRes.res.pitch2D.pitchInBytes = s * sizeof(float);

    cudaTextureDesc texDescr;
    memset(&texDescr, 0, sizeof(cudaTextureDesc));

    texDescr.normalizedCoords = true;
    texDescr.filterMode       = cudaFilterModeLinear;
    texDescr.addressMode[0]   = cudaAddressModeMirror;
    texDescr.addressMode[1]   = cudaAddressModeMirror;
    texDescr.readMode         = cudaReadModeElementType;

    checkCudaErrors(cudaCreateTextureObject(&texSource, &texRes, &texDescr, NULL));
    memset(&texRes, 0, sizeof(cudaResourceDesc));
    texRes.resType                  = cudaResourceTypePitch2D;
    texRes.res.pitch2D.devPtr       = (void *)I1;
    texRes.res.pitch2D.desc         = cudaCreateChannelDesc<float>();
    texRes.res.pitch2D.width        = w;
    texRes.res.pitch2D.height       = h;
    texRes.res.pitch2D.pitchInBytes = s * sizeof(float);
    checkCudaErrors(cudaCreateTextureObject(&texTarget, &texRes, &texDescr, NULL));

    ComputeDerivativesKernel<<<blocks, threads>>>(w, h, s, Ix, Iy, Iz, texSource, texTarget);
}
