affine.hpp

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// SPDX-FileCopyrightText: 2025 Povl Filip Sonne-Frederiksen
//
// SPDX-License-Identifier: GPL-3.0-or-later
 
#pragma once
#include <algorithm>
#include <tuple>
 
namespace reusex::vision::tensor_rt::affine {
 
struct CropResizeMatrix {
  float i2d[6]; // image to dst(network), 2x3 matrix
  float d2i[6]; // dst to image, 2x3 matrix
 
  void compute(const std::tuple<int, int> &from, const std::tuple<int, int> &to,
               const std::tuple<int, int> &start) {
    float scale_x = std::get<0>(to) / (float)std::get<0>(from);
    float scale_y = std::get<1>(to) / (float)std::get<1>(from);
    int start_x = std::get<0>(start);
    int start_y = std::get<1>(start);
 
    // crop resize
    i2d[0] = scale_x;
    i2d[1] = 0.0f;
    i2d[2] = -scale_x * start_x;
    i2d[3] = 0.0f;
    i2d[4] = scale_y;
    i2d[5] = -scale_y * start_y;
 
    double D = i2d[0] * i2d[4] - i2d[1] * i2d[3];
    D = D != 0. ? double(1.) / D : double(0.);
    double A11 = i2d[4] * D, A22 = i2d[0] * D, A12 = -i2d[1] * D,
           A21 = -i2d[3] * D;
    double b1 = -A11 * i2d[2] - A12 * i2d[5];
    double b2 = -A21 * i2d[2] - A22 * i2d[5];
 
    d2i[0] = A11;
    d2i[1] = A12;
    d2i[2] = b1;
    d2i[3] = A21;
    d2i[4] = A22;
    d2i[5] = b2;
  }
};
 
struct ResizeMatrix {
  float i2d[6]; // image to dst(network), 2x3 matrix
  float d2i[6]; // dst to image, 2x3 matrix
 
  void compute(const std::tuple<int, int> &from,
               const std::tuple<int, int> &to) {
    float scale_x = std::get<0>(to) / (float)std::get<0>(from);
    float scale_y = std::get<1>(to) / (float)std::get<1>(from);
    float scale = std::min(scale_x, scale_y);
 
    // resize
    // i2d[0] = scale_x;
    // i2d[1] = 0;
    // i2d[2] = 0;
    // i2d[3] = 0;
    // i2d[4] = scale_y;
    // i2d[5] = 0;
 
    // double D = i2d[0] * i2d[4] - i2d[1] * i2d[3];
    // D = D != 0. ? double(1.) / D : double(0.);
    // double A11 = i2d[4] * D, A22 = i2d[0] * D, A12 = -i2d[1] * D,
    //        A21 = -i2d[3] * D;
    // double b1 = -A11 * i2d[2] - A12 * i2d[5];
    // double b2 = -A21 * i2d[2] - A22 * i2d[5];
 
    // d2i[0] = A11;
    // d2i[1] = A12;
    // d2i[2] = b1;
    // d2i[3] = A21;
    // d2i[4] = A22;
    // d2i[5] = b2;
 
    float inv_scale_x = 1.0f / scale_x;
    float inv_scale_y = 1.0f / scale_y;
 
    d2i[0] = inv_scale_x;
    d2i[1] = 0;
    d2i[3] = 0;
    d2i[4] = inv_scale_y;
 
    // --- Core modification Start ---
    // Add 0.5 offset compensation to match PIL/OpenCV center alignment logic
    // Formula: translation = 0.5 * scale - 0.5
    d2i[2] = 0.5f * inv_scale_x - 0.5f;
    d2i[5] = 0.5f * inv_scale_y - 0.5f;
  }
};
 
struct LetterBoxMatrix {
  float i2d[6]; // image to dst(network), 2x3 matrix
  float d2i[6]; // dst to image, 2x3 matrix
 
  void compute(const std::tuple<int, int> &from,
               const std::tuple<int, int> &to) {
    float scale_x = std::get<0>(to) / (float)std::get<0>(from);
    float scale_y = std::get<1>(to) / (float)std::get<1>(from);
    float scale = std::min(scale_x, scale_y);
 
    // letter box
    i2d[0] = scale;
    i2d[1] = 0;
    i2d[2] = -scale * std::get<0>(from) * 0.5 + std::get<0>(to) * 0.5 +
             scale * 0.5 - 0.5;
    i2d[3] = 0;
    i2d[4] = scale;
    i2d[5] = -scale * std::get<1>(from) * 0.5 + std::get<1>(to) * 0.5 +
             scale * 0.5 - 0.5;
 
    double D = i2d[0] * i2d[4] - i2d[1] * i2d[3];
    D = D != 0. ? double(1.) / D : double(0.);
    double A11 = i2d[4] * D, A22 = i2d[0] * D, A12 = -i2d[1] * D,
           A21 = -i2d[3] * D;
    double b1 = -A11 * i2d[2] - A12 * i2d[5];
    double b2 = -A21 * i2d[2] - A22 * i2d[5];
 
    d2i[0] = A11;
    d2i[1] = A12;
    d2i[2] = b1;
    d2i[3] = A21;
    d2i[4] = A22;
    d2i[5] = b2;
  }
};
 
} // namespace reusex::vision::tensor_rt::affine