affine_grid_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.

#pragma once

#include "paddle/phi/kernels/affine_grid_kernel.h"
#include "paddle/fluid/platform/device/gpu/gpu_device_function.h"
#include "paddle/fluid/platform/device/gpu/gpu_info.h"
#include "paddle/fluid/platform/device/gpu/gpu_primitives.h"
#include "paddle/fluid/platform/device_context.h"
#include "paddle/phi/backends/gpu/gpu_context.h"
#include "paddle/phi/common/int_array.h"
#include "paddle/phi/core/kernel_registry.h"

namespace phi {

template <typename T>
__global__ void LinspaceKernel(T start, T step, int64_t size, T* out) {
  CUDA_KERNEL_LOOP(index, size) { out[index] = start + step * index; }
}

template <typename T>
struct Linspace<phi::GPUContext, T> {
  void operator()(T start,
                  T end,
                  int count,
                  bool align_corners,
                  DenseTensor* numbers,
                  const phi::GPUContext& dev_ctx) {
    numbers->Resize(phi::make_ddim({count}));
    T* number_data = dev_ctx.template Alloc<T>(numbers);
    T slice = (end - start) / (T)(count - 1);
    if (!align_corners) {
      slice = (end - start) / (T)count;
      start *= (T)(count - 1) / (T)count;
    }
    auto stream = dev_ctx.stream();
    int block = 512;
    int grid = (count + block - 1) / block;
    LinspaceKernel<T>
        <<<grid, block, 0, stream>>>(start, slice, count, number_data);
  }
};

template <typename T>
__global__ void affine_grid_kernel(const int count,
                                   int n,
                                   int out_h,
                                   int out_w,
                                   T h_start,
                                   T w_start,
                                   T h_step,
                                   T w_step,
                                   const T* theta,  // N, 2, 3
                                   T* output) {
  CUDA_KERNEL_LOOP(index, count) {
    int w = index % out_w;
    int h = (index / out_w) % out_h;
    int n = index / (out_w * out_h);

    T h_coor = h_step * static_cast<T>(h) + static_cast<T>(h_start);
    T w_coor = w_step * static_cast<T>(w) + static_cast<T>(w_start);

    int theta_offset = n * 6;  // 2 * 3;
    // affine from (h_coor, w_coor) to (x, y)
    output[index * 2] = theta[theta_offset] * w_coor +
                        theta[theta_offset + 1] * h_coor +
                        theta[theta_offset + 2];
    output[index * 2 + 1] = theta[theta_offset + 3] * w_coor +
                            theta[theta_offset + 4] * h_coor +
                            theta[theta_offset + 5];
  }
}

template <typename T, typename Context>
void AffineGridCUDAKernel(const Context& dev_ctx,
                          const DenseTensor& input,
                          const IntArray& outputShape,
                          bool align_corners,
                          DenseTensor* output) {
  auto* theta = &input;
  int n = theta->dims()[0];
  auto& size_attr = outputShape.GetData();
  int h = 0;
  int w = 0;
  h = size_attr[2];
  w = size_attr[3];
  output->Resize(phi::make_ddim({n, h, w, 2}));
  T* out_data = dev_ctx.template Alloc<T>(output);

  T h_step;
  T w_step;
  T h_start = -1;
  T w_start = -1;
  if (align_corners) {
    h_step = static_cast<T>(2) / static_cast<T>(h - 1);
    w_step = static_cast<T>(2) / static_cast<T>(w - 1);
  } else {
    h_step = static_cast<T>(2) / static_cast<T>(h);
    w_step = static_cast<T>(2) / static_cast<T>(w);

    h_start *= static_cast<T>(h - 1) / static_cast<T>(h);
    w_start *= static_cast<T>(w - 1) / static_cast<T>(w);
  }

  const int count = n * h * w;
  int block = 512;
  int grid = (count + block - 1) / block;
  auto cu_stream = dev_ctx.stream();
  affine_grid_kernel<<<grid, block, 0, cu_stream>>>(
      count,
      n,
      h,
      w,
      h_start,
      w_start,
      h_step,
      w_step,
      theta->data<T>(),  // N, 2, 3
      out_data);
}

}  // namespace phi

PD_REGISTER_KERNEL(
    affine_grid, GPU, ALL_LAYOUT, phi::AffineGridCUDAKernel, float, double){};