1 files changed, 179 insertions, 0 deletions
diff --git a/main.cpp b/main.cpp
new file mode 100644
index 0000000..bd03139
--- /dev/null
+++ b/main.cpp
@@ -0,0 +1,179 @@
+#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() { }