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#include <hip/hip_runtime.h>
#include <source_location>
#include <stdexcept>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
inline void hip_check(
hipError_t err,
std::source_location loc = std::source_location::current())
{
if (err != hipSuccess) {
throw std::runtime_error(
std::string(hipGetErrorString(err)) +
" at " + loc.file_name() + ":" + std::to_string(loc.line()));
}
}
struct PyramidLevel {
int width = 0;
int height = 0;
float4* color_smax = nullptr; /* rgb s_max*/
float4* tensor = nullptr; /* x=E, y=F, z=G, w= */
};
struct KuwaharaPyramid {
std::vector<PyramidLevel> levels; /* 0 = finest, back() = coarsest */
};
struct KuwaharaParams {
float radius;
float alpha;
int num_sectors; /* 4 or 8 */
float q;
float tau_w;
float p_s, p_d, tau_v;
};
/* allocations */
PyramidLevel make_level(int width, int height) {
PyramidLevel lvl{width, height};
hip_check(hipMalloc(&lvl.color_smax, sizeof(float4) * width * height));
hip_check(hipMalloc(&lvl.tensor, sizeof(float4) * width * height));
return lvl;
}
void free_level(PyramidLevel& lvl) {
hipFree(lvl.color_smax);
hipFree(lvl.tensor);
lvl.color_smax = nullptr;
lvl.tensor = nullptr;
}
KuwaharaPyramid make_pyramid(int base_width, int base_height, int num_levels) {
KuwaharaPyramid pyr;
pyr.levels.reserve(num_levels);
int w = base_width, h = base_height;
for (int i = 0; i < num_levels; ++i) {
pyr.levels.push_back(make_level(w, h));
w = std::max(1, w / 2);
h = std::max(1, h / 2);
}
return pyr;
}
void destroy_pyramid(KuwaharaPyramid& pyr) {
for (auto& lvl : pyr.levels) {
free_level(lvl);
}
pyr.levels.clear();
}
/* Lanczos3 downsample */
__device__ __forceinline__ float lanczos3(float x) {
const float a = 3.0f;
if (x == 0.0f) return 1.0f;
if (x <= -a || x >= a) {
return 0.0f;
}
const float px = M_PI * x;
return (a * sinf(px) * sinf(px / a)) / (px * px);
}
__device__ float4 lanczos3_sample_axis(
const float4* src, int src_len, int src_stride, int src_base, int dst_idx, float scale)
{
float center = (dst_idx + 0.5f) * scale - 0.5f;
int icenter = static_cast<int>(floorf(center));
float filter_scale = fmaxf(scale, 1.0f);
int radius = static_cast<int>(ceilf(3.0f * filter_scale));
float4 sum = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
float wsum = 0.0f;
for (int i = icenter - radius; i <= icenter + radius; ++i) {
int clamped = min(max(i, 0), src_len - 1);
float w = lanczos3((i - center) / filter_scale);
const float4& s = src[src_base + clamped * src_stride];
sum.x += s.x * w;
sum.y += s.y * w;
sum.z += s.z * w;
sum.w += s.w * w;
wsum += w;
}
if (wsum > 1e-6f) {
sum.x /= wsum;
sum.y /= wsum;
sum.z /= wsum;
sum.w /= wsum;
}
return sum;
}
__global__ void downsample_horizontal(
const float4* src, int src_w, int h,
float4* dst, int dst_w, float scale_x)
{
int x = blockIdx.x * blockDim.x + threadIdx.x;
int y = blockIdx.y * blockDim.y + threadIdx.y;
if (x >= dst_w || y >= h) {
return;
}
int src_row_base = y * src_w;
dst[y * dst_w + x] =
lanczos3_sample_axis(src, src_w, 1, src_row_base, x, scale_x);
}
__global__ void downsample_vertical(
const float4* src, int w, int src_h,
float4* dst, int dst_h, float scale_y)
{
int x = blockIdx.x * blockDim.x + threadIdx.x;
int y = blockIdx.y * blockDim.y + threadIdx.y;
if (x >= w || y >= dst_h) return;
dst[y * w + x] =
lanczos3_sample_axis(src, src_h, w, x, y, scale_y);
}
void downsample_level(const PyramidLevel& src, PyramidLevel& dst) {
float scale_x = static_cast<float>(src.width) / dst.width;
float scale_y = static_cast<float>(src.height) / dst.height;
float4* tmp;
hip_check(hipMalloc(&tmp, sizeof(float4) * dst.width * src.height));
dim3 block(16, 16);
dim3 grid_h((dst.width + block.x - 1) / block.x,
(src.height + block.y - 1) / block.y);
downsample_horizontal<<<grid_h, block>>>(
src.color_smax, src.width, src.height, tmp, dst.width, scale_x);
hip_check(hipGetLastError());
dim3 grid_v((dst.width + block.x - 1) / block.x,
(dst.height + block.y - 1) / block.y);
downsample_vertical<<<grid_v, block>>>(
tmp, dst.width, src.height, dst.color_smax, dst.height, scale_y);
hip_check(hipGetLastError());
hipFree(tmp);
}
void build_pyramid(KuwaharaPyramid& pyr) {
for (size_t i = 1; i < pyr.levels.size(); ++i) {
downsample_level(pyr.levels[i - 1], pyr.levels[i]);
}
}
int main() { }
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