grid_sample_kernel.cu

// Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "paddle/phi/kernels/grid_sample_kernel.h"

#include "paddle/phi/backends/gpu/gpu_info.h"
#include "paddle/phi/backends/gpu/gpu_launch_config.h"
#include "paddle/phi/core/kernel_registry.h"
#include "paddle/phi/kernels/gpu/grid_sample_utils.h"

namespace phi {

template <typename T>
static __forceinline__ __device__ T Unnormalize(T coord,
                                                int size,
                                                bool align_corners) {
  if (align_corners) {
    return ((coord + 1.f) / 2) * (size - 1);
  } else {
    return ((coord + 1.f) * size - 1) / 2;
  }
}

template <typename T>
static __forceinline__ __device__ T ClipIndexes(T in, int max_value) {
  return min(static_cast<T>(max_value), max(in, static_cast<T>(0)));
}

template <typename T>
static __forceinline__ __device__ T ReflectIndexes(T in,
                                                   int twice_low,
                                                   int twice_high) {
  if (twice_low == twice_high) {
    return static_cast<T>(0);
  }
  T min = static_cast<T>(twice_low) / 2;
  T span = static_cast<T>(twice_high - twice_low) / 2;
  in = fabs(in - min);
  T extra = fmod(in, span);
  int flips = static_cast<int>(floor(in / span));
  if (flips % 2 == 0) {
    return extra + min;
  } else {
    return span - extra + min;
  }
}

template <typename T>
static __forceinline__ __device__ T ComputePositions(T coord,
                                                     int size,
                                                     PaddingMode padding_mode,
                                                     bool align_corners) {
  coord = Unnormalize<T>(coord, size, align_corners);
  if (padding_mode == PaddingMode::border) {
    coord = ClipIndexes(coord, size - 1);
  } else if (padding_mode == PaddingMode::reflect) {
    if (align_corners) {
      coord = ReflectIndexes(coord, 0, 2 * (size - 1));
    } else {
      coord = ReflectIndexes(coord, -1, 2 * size - 1);
    }
    coord = ClipIndexes(coord, size - 1);
  }
  return coord;
}

template <typename T>
__global__ void GridSampleCudaKernel(const int nthreads,
                                     int n,
                                     int out_c,
                                     int out_h,
                                     int out_w,
                                     int in_h,
                                     int in_w,
                                     const T* input,
                                     const T* grid,
                                     T* output,
                                     const Mode mode,
                                     const PaddingMode padding_mode,
                                     bool align_corners) {
  int inp_sN = out_c * in_h * in_w;

  int inp_sC = in_h * in_w;
  int inp_sH = in_w;
  int inp_sW = 1;
  int grid_sN = out_h * out_w * 2;
  int grid_sH = out_w * 2;
  int grid_sW = 2;
  int grid_sCoor = 1;
  int out_sN = out_c * out_h * out_w;
  int out_sC = out_h * out_w;
  int out_sH = out_w;
  int out_sW = 1;
  CUDA_KERNEL_LOOP(index, nthreads) {
    const int w = index % out_w;
    const int h = (index / out_w) % out_h;
    const int n = index / (out_h * out_w);
    const int grid_offset = n * grid_sN + h * grid_sH + w * grid_sW;

    T ix = grid[grid_offset];
    T iy = grid[grid_offset + grid_sCoor];

    ix = ComputePositions(ix, in_w, padding_mode, align_corners);
    iy = ComputePositions(iy, in_h, padding_mode, align_corners);
    if (mode == Mode::bilinear) {
      int ix_nw = static_cast<int>(floor(ix));
      int iy_nw = static_cast<int>(floor(iy));
      int ix_ne = ix_nw + 1;
      int iy_ne = iy_nw;
      int ix_sw = ix_nw;
      int iy_sw = iy_nw + 1;
      int ix_se = ix_nw + 1;
      int iy_se = iy_nw + 1;

      T nw = (ix_se - ix) * (iy_se - iy);
      T ne = (ix - ix_sw) * (iy_sw - iy);
      T sw = (ix_ne - ix) * (iy - iy_ne);
      T se = (ix - ix_nw) * (iy - iy_nw);

      auto inp_offset_NC = n * inp_sN;

      auto out_ptr_NCHW = output + n * out_sN + h * out_sH + w * out_sW;
      for (int c = 0; c < out_c;
           ++c, inp_offset_NC += inp_sC, out_ptr_NCHW += out_sC) {
        *out_ptr_NCHW = static_cast<T>(0);
        if (InBounds(iy_nw, ix_nw, in_h, in_w)) {
          *out_ptr_NCHW +=
              input[inp_offset_NC + iy_nw * inp_sH + ix_nw * inp_sW] * nw;
        }
        if (InBounds(iy_ne, ix_ne, in_h, in_w)) {
          *out_ptr_NCHW +=
              input[inp_offset_NC + iy_ne * inp_sH + ix_ne * inp_sW] * ne;
        }
        if (InBounds(iy_sw, ix_sw, in_h, in_w)) {
          *out_ptr_NCHW +=
              input[inp_offset_NC + iy_sw * inp_sH + ix_sw * inp_sW] * sw;
        }
        if (InBounds(iy_se, ix_se, in_h, in_w)) {
          *out_ptr_NCHW +=
              input[inp_offset_NC + iy_se * inp_sH + ix_se * inp_sW] * se;
        }
      }
    } else if (mode == Mode::nearest) {
      int ix_nearest = static_cast<int>(std::nearbyint(ix));
      int iy_nearest = static_cast<int>(std::nearbyint(iy));
      auto inp_offset_NC = n * inp_sN;
      auto out_ptr_NCHW = output + n * out_sN + h * out_sH + w * out_sW;
      for (int c = 0; c < out_c;
           ++c, inp_offset_NC += inp_sC, out_ptr_NCHW += out_sC) {
        if (InBounds(iy_nearest, ix_nearest, in_h, in_w)) {
          *out_ptr_NCHW =
              input[inp_offset_NC + iy_nearest * inp_sH + ix_nearest * inp_sW];
        } else {
          *out_ptr_NCHW = static_cast<T>(0);
        }
      }
    }
  }
}

template <typename T>
__global__ void GridSample3DCudaKernel(const int nthreads,
                                       int out_c,
                                       int out_d,
                                       int out_h,
                                       int out_w,
                                       int in_d,
                                       int in_h,
                                       int in_w,
                                       const T* input,
                                       const T* grid,
                                       T* output,
                                       const Mode interpolation_mode,
                                       const PaddingMode padding_mode,
                                       bool align_corners) {
  int inp_sW = 1;
  int inp_sH = in_w;
  int inp_sD = in_h * in_w;
  int inp_sC = in_d * inp_sD;
  int inp_sN = out_c * inp_sC;

  int grid_sCoor = 1;
  int grid_sW = 3;
  int grid_sH = out_w * grid_sW;
  int grid_sD = out_h * grid_sH;
  int grid_sN = out_d * grid_sD;

  int out_sW = 1;
  int out_sH = out_w;
  int out_sD = out_h * out_w;
  int out_sC = out_d * out_sD;
  int out_sN = out_c * out_sC;

  CUDA_KERNEL_LOOP_TYPE(index, nthreads, int) {
    const int w = index % out_w;
    const int h = (index / out_w) % out_h;
    const int d = (index / (out_h * out_w)) % out_d;
    const int n = index / (out_d * out_h * out_w);
    const int grid_offset =
        n * grid_sN + d * grid_sD + h * grid_sH + w * grid_sW;
    // get the corresponding input x, y, z co-ordinates from grid
    T ix = grid[grid_offset];
    T iy = grid[grid_offset + grid_sCoor];
    T iz = grid[grid_offset + 2 * grid_sCoor];
    ix = ComputePositions(ix, in_w, padding_mode, align_corners);
    iy = ComputePositions(iy, in_h, padding_mode, align_corners);
    iz = ComputePositions(iz, in_d, padding_mode, align_corners);
    if (interpolation_mode == Mode::bilinear) {
      // get corner pixel values from (x, y, z)
      // for 4d, we used north-east-south-west
      // for 5d, we add top-bottom
      int ix_tnw = static_cast<int>(std::floor(ix));
      int iy_tnw = static_cast<int>(std::floor(iy));
      int iz_tnw = static_cast<int>(std::floor(iz));

      int ix_tne = ix_tnw + 1;
      int iy_tne = iy_tnw;
      int iz_tne = iz_tnw;

      int ix_tsw = ix_tnw;
      int iy_tsw = iy_tnw + 1;
      int iz_tsw = iz_tnw;

      int ix_tse = ix_tnw + 1;
      int iy_tse = iy_tnw + 1;
      int iz_tse = iz_tnw;

      int ix_bnw = ix_tnw;
      int iy_bnw = iy_tnw;
      int iz_bnw = iz_tnw + 1;

      int ix_bne = ix_tnw + 1;
      int iy_bne = iy_tnw;
      int iz_bne = iz_tnw + 1;

      int ix_bsw = ix_tnw;
      int iy_bsw = iy_tnw + 1;
      int iz_bsw = iz_tnw + 1;

      int ix_bse = ix_tnw + 1;
      int iy_bse = iy_tnw + 1;
      int iz_bse = iz_tnw + 1;

      // get surfaces to each neighbor:
      T tnw = (ix_bse - ix) * (iy_bse - iy) * (iz_bse - iz);
      T tne = (ix - ix_bsw) * (iy_bsw - iy) * (iz_bsw - iz);
      T tsw = (ix_bne - ix) * (iy - iy_bne) * (iz_bne - iz);
      T tse = (ix - ix_bnw) * (iy - iy_bnw) * (iz_bnw - iz);
      T bnw = (ix_tse - ix) * (iy_tse - iy) * (iz - iz_tse);
      T bne = (ix - ix_tsw) * (iy_tsw - iy) * (iz - iz_tsw);
      T bsw = (ix_tne - ix) * (iy - iy_tne) * (iz - iz_tne);
      T bse = (ix - ix_tnw) * (iy - iy_tnw) * (iz - iz_tnw);

      auto inp_ptr_NC = input + n * inp_sN;
      auto out_ptr_NCDHW =
          output + n * out_sN + d * out_sD + h * out_sH + w * out_sW;
      for (int c = 0; c < out_c;
           ++c, inp_ptr_NC += inp_sC, out_ptr_NCDHW += out_sC) {
        *out_ptr_NCDHW = static_cast<T>(0);
        if (InBounds3D(iz_tnw, iy_tnw, ix_tnw, in_d, in_h, in_w)) {
          *out_ptr_NCDHW +=
              inp_ptr_NC[iz_tnw * inp_sD + iy_tnw * inp_sH + ix_tnw * inp_sW] *
              tnw;
        }
        if (InBounds3D(iz_tne, iy_tne, ix_tne, in_d, in_h, in_w)) {
          *out_ptr_NCDHW +=
              inp_ptr_NC[iz_tne * inp_sD + iy_tne * inp_sH + ix_tne * inp_sW] *
              tne;
        }
        if (InBounds3D(iz_tsw, iy_tsw, ix_tsw, in_d, in_h, in_w)) {
          *out_ptr_NCDHW +=
              inp_ptr_NC[iz_tsw * inp_sD + iy_tsw * inp_sH + ix_tsw * inp_sW] *
              tsw;
        }
        if (InBounds3D(iz_tse, iy_tse, ix_tse, in_d, in_h, in_w)) {
          *out_ptr_NCDHW +=
              inp_ptr_NC[iz_tse * inp_sD + iy_tse * inp_sH + ix_tse * inp_sW] *
              tse;
        }
        if (InBounds3D(iz_bnw, iy_bnw, ix_bnw, in_d, in_h, in_w)) {
          *out_ptr_NCDHW +=
              inp_ptr_NC[iz_bnw * inp_sD + iy_bnw * inp_sH + ix_bnw * inp_sW] *
              bnw;
        }
        if (InBounds3D(iz_bne, iy_bne, ix_bne, in_d, in_h, in_w)) {
          *out_ptr_NCDHW +=
              inp_ptr_NC[iz_bne * inp_sD + iy_bne * inp_sH + ix_bne * inp_sW] *
              bne;
        }
        if (InBounds3D(iz_bsw, iy_bsw, ix_bsw, in_d, in_h, in_w)) {
          *out_ptr_NCDHW +=
              inp_ptr_NC[iz_bsw * inp_sD + iy_bsw * inp_sH + ix_bsw * inp_sW] *
              bsw;
        }
        if (InBounds3D(iz_bse, iy_bse, ix_bse, in_d, in_h, in_w)) {
          *out_ptr_NCDHW +=
              inp_ptr_NC[iz_bse * inp_sD + iy_bse * inp_sH + ix_bse * inp_sW] *
              bse;
        }
      }
    } else if (interpolation_mode == Mode::nearest) {
      int ix_nearest = static_cast<int>(std::round(ix));
      int iy_nearest = static_cast<int>(std::round(iy));
      int iz_nearest = static_cast<int>(std::round(iz));

      // assign nearest neighor pixel value to output pixel
      auto inp_ptr_NC = input + n * inp_sN;
      auto out_ptr_NCDHW =
          output + n * out_sN + d * out_sD + h * out_sH + w * out_sW;
      for (int c = 0; c < out_c;
           ++c, inp_ptr_NC += inp_sC, out_ptr_NCDHW += out_sC) {
        if (InBounds3D(iz_nearest, iy_nearest, ix_nearest, in_d, in_h, in_w)) {
          *out_ptr_NCDHW =
              inp_ptr_NC[iz_nearest * inp_sD + iy_nearest * inp_sH +
                         ix_nearest * inp_sW];
        } else {
          *out_ptr_NCDHW = static_cast<T>(0);
        }
      }
    }
  }
}

template <typename T, typename Context>
void GridSampleKernel(const Context& dev_ctx,
                      const DenseTensor& x,
                      const DenseTensor& grid,
                      const std::string& mode,
                      const std::string& padding_mode,
                      bool align_corners,
                      DenseTensor* out) {
  PaddingMode enum_padding_mode;
  Mode enum_mode;
  if (padding_mode == "border") {
    enum_padding_mode = PaddingMode::border;
  } else if (padding_mode == "reflection") {
    enum_padding_mode = PaddingMode::reflect;
  } else {
    enum_padding_mode = PaddingMode::zeros;
  }

  if (mode == "nearest") {
    enum_mode = Mode::nearest;
  } else {
    enum_mode = Mode::bilinear;
  }

  if (x.dims().size() == 4) {
    const int n = grid.dims()[0];
    const int out_h = grid.dims()[1];
    const int out_w = grid.dims()[2];
    const int c = x.dims()[1];
    const int in_h = x.dims()[2];
    const int in_w = x.dims()[3];
    VLOG(3) << "n: " << n << "; c: " << c << "; out_h: " << out_h
            << "; out_w: " << out_w;

    auto* output_data = dev_ctx.template Alloc<T>(out);
    VLOG(3) << "out dims: " << out->dims()[0] << "; " << out->dims()[1] << "; "
            << out->dims()[2] << "; " << out->dims()[3];

    int count = static_cast<int>(n * out_h * out_w);
    auto cu_stream = dev_ctx.stream();
    backends::gpu::GpuLaunchConfig config =
        backends::gpu::GetGpuLaunchConfig1D(dev_ctx, count);
    GridSampleCudaKernel<T>
        <<<config.block_per_grid, config.thread_per_block, 0, cu_stream>>>(
            count,
            n,
            c,
            out_h,
            out_w,
            in_h,
            in_w,
            x.data<T>(),
            grid.data<T>(),
            output_data,
            enum_mode,
            enum_padding_mode,
            align_corners);
  } else {
    const int n = grid.dims()[0];
    const int out_d = grid.dims()[1];
    const int out_h = grid.dims()[2];
    const int out_w = grid.dims()[3];
    const int c = x.dims()[1];
    const int in_d = x.dims()[2];
    const int in_h = x.dims()[3];
    const int in_w = x.dims()[4];

    VLOG(3) << "n: " << n << "; c: " << c << "; out_d: " << out_d
            << "; out_h: " << out_h << "; out_w: " << out_w;

    auto* output_data = dev_ctx.template Alloc<T>(out);
    VLOG(3) << "out dims: " << out->dims()[0] << "; " << out->dims()[1] << "; "
            << out->dims()[2] << "; " << out->dims()[3] << "; "
            << out->dims()[4];

    int count = static_cast<int>(n * out_d * out_h * out_w);
    auto cu_stream = dev_ctx.stream();
    backends::gpu::GpuLaunchConfig config =
        backends::gpu::GetGpuLaunchConfig1D(dev_ctx, count);
    GridSample3DCudaKernel<T>
        <<<config.block_per_grid, config.thread_per_block, 0, cu_stream>>>(
            count,
            c,
            out_d,
            out_h,
            out_w,
            in_d,
            in_h,
            in_w,
            x.data<T>(),
            grid.data<T>(),
            output_data,
            enum_mode,
            enum_padding_mode,
            align_corners);
  }
}

}  // namespace phi

PD_REGISTER_KERNEL(
    grid_sample, GPU, ALL_LAYOUT, phi::GridSampleKernel, float, double) {}