Add WSL Windows cross build script

.gitignore

@@ -1,5 +1,6 @@
 build/
 build-windows/
+build-wsl-windows/
 cmake-build-*/
 .qt/
 .qtc/

build_wsl_windows.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if ! command -v x86_64-w64-mingw32-g++ >/dev/null 2>&1; then
+    echo "Missing x86_64-w64-mingw32-g++."
+    echo "Install it in WSL with: sudo apt install mingw-w64"
+    exit 1
+fi
+
+if [[ "${QT_MINGW_PREFIX:-}" == "" ]]; then
+    echo "Missing QT_MINGW_PREFIX."
+    echo "Example: export QT_MINGW_PREFIX=/opt/mxe/usr/x86_64-w64-mingw32.shared/qt6"
+    exit 1
+fi
+
+if [[ "${OpenCV_DIR:-}" == "" ]]; then
+    echo "Missing OpenCV_DIR."
+    echo "Example: export OpenCV_DIR=/opt/mxe/usr/x86_64-w64-mingw32.shared/lib/cmake/opencv4"
+    exit 1
+fi
+
+cmake -S . -B build-wsl-windows \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/mingw64.cmake \
+    -DCMAKE_PREFIX_PATH="${QT_MINGW_PREFIX}" \
+    -DOpenCV_DIR="${OpenCV_DIR}"
+
+cmake --build build-wsl-windows --config Release
+
+echo "Windows executable should be under build-wsl-windows/."

cmake/toolchains/mingw64.cmake

@@ -0,0 +1,11 @@
+set(CMAKE_SYSTEM_NAME Windows)
+set(CMAKE_SYSTEM_PROCESSOR x86_64)
+
+set(CMAKE_C_COMPILER x86_64-w64-mingw32-gcc)
+set(CMAKE_CXX_COMPILER x86_64-w64-mingw32-g++)
+set(CMAKE_RC_COMPILER x86_64-w64-mingw32-windres)
+
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

readme.md

@@ -87,6 +87,26 @@ windeployqt QtOpenCVImageTool.exe
 
 然后把 OpenCV 的运行库 DLL 一并复制到 exe 所在目录，例如 `opencv_world*.dll` 或相关 `opencv_*.dll`。
 
+## WSL 中交叉编译 Windows 程序
+
+WSL 里不能使用 Linux 版 Qt/OpenCV 直接生成 Windows exe，必须准备 Windows 目标库。推荐使用 MinGW-w64 作为交叉编译器，并准备同为 MinGW-w64 目标的 Qt 和 OpenCV。
+
+需要的组件：
+
+- `x86_64-w64-mingw32-g++`
+- Windows/MinGW 目标 Qt，目录中应包含 `Qt6Config.cmake` 或 `Qt5Config.cmake`
+- Windows/MinGW 目标 OpenCV，目录中应包含 `OpenCVConfig.cmake`
+
+构建脚本：
+
+```bash
+export QT_MINGW_PREFIX=/opt/mxe/usr/x86_64-w64-mingw32.shared/qt6
+export OpenCV_DIR=/opt/mxe/usr/x86_64-w64-mingw32.shared/lib/cmake/opencv4
+./build_wsl_windows.sh
+```
+
+如果使用的是自己编译或复制来的 Windows 目标 Qt/OpenCV，把上面两个路径换成实际路径即可。
+
 ## 说明
 
 本示例中的分类属于简单规则分类，适合作为课程作业演示：根据图像整体亮度判断“偏亮/偏暗/亮度适中”，根据 BGR 平均值判断主色。若需要更高精度分类，可替换为训练好的 OpenCV DNN 或传统机器学习模型。