Merge pull request #28423 from Chevi-Koren:fix-clp-vcpkg-final

Fix Clp library detection for vcpkg on Windows #28423

## Problem

Building OpenCV with `WITH_CLP=ON` on Windows (vcpkg) fails:

LINK : fatal error LNK1181: cannot open input file 'libClp.lib'

vcpkg generates `Clp.lib` and `CoinUtils.lib`, but OpenCV expected `libClp.lib`/`libCoinUtils.lib`.

## Solution

Modernize CLP detection with a robust, platform-aware approach:

1. **CMake `find_package(Clp CONFIG)`**: detects vcpkg and uses imported targets (`Coin::Clp`, `Coin::CoinUtils`)
2. **Fallback**: pkg-config on Unix/Linux  
3. **Skip** Android/iOS

## Benefits

✅ Fixes Windows build with vcpkg  
✅ Uses modern CMake targets  
✅ Backward compatible with Unix/Linux  
✅ Safe for CI and mobile builds  
✅ Graceful fallback if CLP unavailable  

## Testing

- **Windows 11 + vcpkg**: build succeeds
- **No CLP installed**: configure/build succeeds  
- **Linux/Unix**: existing workflows unaffected
- **Android/iOS**: properly skipped

## Changes

- Update `cmake/OpenCVFindLibsPerf.cmake`
- Replace hardcoded library names with CMake targets
- Add mobile platform guards
- Preserve backward compatibility

Fixes #26592

---

### Pull Request Readiness Checklist

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch (`4.x`)
- [x] There is a reference to the original bug report and related work (#26592)
- [x] The feature is well documented and sample code can be built with the project CMake
- [x] No additional tests required - this is a build system fix that maintains existing functionality

CMakeLists.txt

@@ -1871,6 +1871,10 @@ if(WITH_EIGEN OR HAVE_EIGEN)
   status("    Eigen:"      HAVE_EIGEN       THEN "YES (ver ${EIGEN_WORLD_VERSION}.${EIGEN_MAJOR_VERSION}.${EIGEN_MINOR_VERSION})" ELSE NO)
 endif()
 
+if(WITH_CLP OR HAVE_CLP)
+  status("    CLP:"        HAVE_CLP         THEN "YES" ELSE NO)
+endif()
+
 if(WITH_OPENVX OR HAVE_OPENVX)
   status("    OpenVX:"     HAVE_OPENVX      THEN "YES (${OPENVX_LIBRARIES})" ELSE "NO")
 endif()

cmake/OpenCVFindLibsPerf.cmake

@@ -130,43 +130,71 @@ if(HAVE_EIGEN)
   endif()
 endif()
 
+
 # --- Clp ---
 # Ubuntu: sudo apt-get install coinor-libclp-dev coinor-libcoinutils-dev
 ocv_clear_vars(HAVE_CLP)
-if(WITH_CLP)
-  if(UNIX)
-    ocv_check_modules(CLP clp)
-    if(CLP_FOUND)
-      set(HAVE_CLP TRUE)
-      if(NOT ${CLP_INCLUDE_DIRS} STREQUAL "")
-        ocv_include_directories(${CLP_INCLUDE_DIRS})
+
+if(WITH_CLP AND NOT ANDROID AND NOT IOS)
+
+  # 1. Modern CMake config (vcpkg / system packages)
+  find_package(Clp CONFIG QUIET)
+  if(Clp_FOUND AND TARGET Coin::Clp AND TARGET Coin::CoinUtils)
+    set(HAVE_CLP 1)
+    list(APPEND OPENCV_LINKER_LIBS Coin::Clp Coin::CoinUtils)
+  endif()
+
+  # 2. pkg-config fallback (Unix)
+  if(NOT HAVE_CLP AND UNIX)
+    find_package(PkgConfig QUIET)
+    if(PKG_CONFIG_FOUND)
+      pkg_check_modules(CLP QUIET clp)
+      if(CLP_FOUND)
+        set(HAVE_CLP 1)
+        ocv_include_directories(SYSTEM ${CLP_INCLUDE_DIRS})
+        list(APPEND OPENCV_LINKER_LIBS ${CLP_LIBRARIES})
       endif()
-      list(APPEND OPENCV_LINKER_LIBS ${CLP_LIBRARIES})
     endif()
   endif()
 
-  if(NOT CLP_FOUND)
-    find_path(CLP_INCLUDE_PATH "coin"
-              PATHS "/usr/local/include" "/usr/include" "/opt/include"
-              DOC "The path to Clp headers")
+  # 3. Manual fallback (last resort)
+  if(NOT HAVE_CLP)
+    find_path(CLP_INCLUDE_PATH
+      NAMES coin/ClpSimplex.hpp
+      PATHS /usr/include /usr/local/include /opt/include
+      DOC "The path to Clp headers"
+    )
+
     if(CLP_INCLUDE_PATH)
-      ocv_include_directories(${CLP_INCLUDE_PATH} "${CLP_INCLUDE_PATH}/coin")
-      get_filename_component(_CLP_LIBRARY_DIR "${CLP_INCLUDE_PATH}/../lib" ABSOLUTE)
-      set(CLP_LIBRARY_DIR "${_CLP_LIBRARY_DIR}" CACHE PATH "Full path of Clp library directory")
-      link_directories(${CLP_LIBRARY_DIR})
-      if(UNIX)
-        set(OPENCV_LINKER_LIBS ${OPENCV_LINKER_LIBS} Clp CoinUtils m)
-      else()
-        if(MINGW)
-            set(OPENCV_LINKER_LIBS ${OPENCV_LINKER_LIBS} Clp CoinUtils)
-        else()
-            set(OPENCV_LINKER_LIBS ${OPENCV_LINKER_LIBS} libClp libCoinUtils)
+      # Support both:
+      #   /usr/include/coin/ClpSimplex.hpp
+      #   /usr/local/include/ClpSimplex.hpp + /coin
+      ocv_include_directories(
+        ${CLP_INCLUDE_PATH}
+        "${CLP_INCLUDE_PATH}/coin"
+      )
+
+      find_library(CLP_LIBRARY
+        NAMES Clp libClp
+      )
+      find_library(COINUTILS_LIBRARY
+        NAMES CoinUtils libCoinUtils
+      )
+
+      if(CLP_LIBRARY AND COINUTILS_LIBRARY)
+        set(HAVE_CLP 1)
+        list(APPEND OPENCV_LINKER_LIBS
+          ${CLP_LIBRARY}
+          ${COINUTILS_LIBRARY}
+        )
+        if(UNIX)
+          list(APPEND OPENCV_LINKER_LIBS m)
         endif()
       endif()
-      set(HAVE_CLP TRUE)
     endif()
   endif()
-endif(WITH_CLP)
+
+endif()
 
 # --- ARM KleidiCV
 if(WITH_KLEIDICV)
@@ -219,4 +247,4 @@ if(WITH_FASTCV)
       set(HAVE_FASTCV FALSE CACHE BOOL "FastCV status")
     endif()
   endif()
-endif(WITH_FASTCV)
+endif(WITH_FASTCV)