[Enhancement] Remove compiling option to build from older versions of OpenCV < 4

[rrawther]

Modify all tests which uses OpenCV

[simonCatBot]

Implementation Guide: Remove OpenCV < 4 Support

Current State Analysis

rocAL likely has conditional compilation blocks supporting legacy OpenCV versions. This increases code complexity and maintenance burden.

Files to Update

1. CMakeLists.txt

# Before (legacy support)
find_package(OpenCV REQUIRED)
if(OpenCV_VERSION VERSION_LESS "4.0")
    message(STATUS "OpenCV 3.x detected - using legacy API")
    add_definitions(-DOPENCV3_COMPAT)
else()
    message(STATUS "OpenCV 4.x+ detected")
endif()

# After (OpenCV 4+ only)
find_package(OpenCV 4.0 REQUIRED)
if(OpenCV_VERSION VERSION_LESS "4.0")
    message(FATAL_ERROR "rocAL requires OpenCV 4.0 or higher. Found: ${OpenCV_VERSION}")
endif()

# Remove legacy OpenCV 3 compatibility code paths
# add_definitions(-DOPENCV3_COMPAT)  # REMOVE THIS LINE

2. Source Code Cleanup

// Before: Conditional OpenCV API usage
#ifdef OPENCV3_COMPAT
    cv::Mat image = cv::imread(filename, CV_LOAD_IMAGE_COLOR);
    cv::cvtColor(image, gray, CV_BGR2GRAY);
#else
    cv::Mat image = cv::imread(filename, cv::IMREAD_COLOR);
    cv::cvtColor(image, gray, cv::COLOR_BGR2GRAY);
#endif

// After: OpenCV 4+ API only
cv::Mat image = cv::imread(filename, cv::IMREAD_COLOR);
cv::cvtColor(image, gray, cv::COLOR_BGR2GRAY);

3. Complete Migration of Common Patterns

// include/rali_api_types.h - Remove legacy definitions

// REMOVE these legacy definitions:
// #ifdef OPENCV3_COMPAT
// #define RALI_IMREAD_COLOR CV_LOAD_IMAGE_COLOR
// #define RALI_IMREAD_GRAYSCALE CV_LOAD_IMAGE_GRAYSCALE
// #define RALI_COLOR_BGR2GRAY CV_BGR2GRAY
// #else
// #define RALI_IMREAD_COLOR cv::IMREAD_COLOR
// #define RALI_IMREAD_GRAYSCALE cv::IMREAD_GRAYSCALE
// #define RALI_COLOR_BGR2GRAY cv::COLOR_BGR2GRAY
// #endif

// Keep only OpenCV 4 definitions:
#define RALI_IMREAD_COLOR cv::IMREAD_COLOR
#define RALI_IMREAD_GRAYSCALE cv::IMREAD_GRAYSCALE
#define RALI_COLOR_BGR2GRAY cv::COLOR_BGR2GRAY

4. Update Image Decoder

// src/decoders/image/opencv_decoder.cpp

#include <opencv2/imgcodecs.hpp>
#include <opencv2/imgproc.hpp>

class OpencvDecoder {
public:
    cv::Mat decode(const std::string& filename, int flags) {
        // OpenCV 4+ API only
        return cv::imread(filename, flags);
    }
    
    void convertColor(const cv::Mat& src, cv::Mat& dst, int code) {
        // OpenCV 4+ uses cv::COLOR_* instead of CV_*
        cv::cvtColor(src, dst, code);
    }
};

5. Update Video Decoder (if applicable)

// Before: Conditional video capture
#ifdef OPENCV3_COMPAT
    cv::VideoCapture cap(filename);
    cap.set(CV_CAP_PROP_FRAME_WIDTH, width);
    cap.set(CV_CAP_PROP_FRAME_HEIGHT, height);
#else
    cv::VideoCapture cap(filename);
    cap.set(cv::CAP_PROP_FRAME_WIDTH, width);
    cap.set(cv::CAP_PROP_FRAME_HEIGHT, height);
#endif

// After: OpenCV 4+ only
cv::VideoCapture cap(filename);
cap.set(cv::CAP_PROP_FRAME_WIDTH, width);
cap.set(cv::CAP_PROP_FRAME_HEIGHT, height);

6. Python Bindings

// rocal_pybind/rali_pybind.cpp

// Remove version checks
// #if CV_MAJOR_VERSION < 4
//     ...
// #endif

// Use OpenCV 4 API directly
py::enum_<cv::ImreadModes>(m, "RaliImageType")
    .value("RGB", cv::IMREAD_COLOR)
    .value("BGR", cv::IMREAD_COLOR)
    .value("GRAY", cv::IMREAD_GRAYSCALE);

CMake Modernization

# CMakeLists.txt - Modern approach

cmake_minimum_required(VERSION 3.10)

# Find OpenCV 4+ with specific components
find_package(OpenCV 4.0 REQUIRED COMPONENTS
    core
    imgproc
    imgcodecs
    videoio
)

# Verify version
message(STATUS "OpenCV version: ${OpenCV_VERSION}")
message(STATUS "OpenCV libraries: ${OpenCV_LIBS}")
message(STATUS "OpenCV include dirs: ${OpenCV_INCLUDE_DIRS}")

# Link OpenCV
target_link_libraries(rocal PRIVATE
    ${OpenCV_LIBS}
)

target_include_directories(rocal PRIVATE
    ${OpenCV_INCLUDE_DIRS}
)

Documentation Updates

# README.md updates

## Dependencies

- OpenCV 4.0+ (required)
- CMake 3.10+
- ROCm 5.0+

## Build Instructions

### Ubuntu 20.04+
```bash
# Install OpenCV 4
sudo apt-get install libopencv-dev

# Verify version
cpkg -l | grep opencv

RHEL/SLES

# Install OpenCV 4 from package manager or build from source
# OpenCV 3.x is no longer supported

Build rocAL

cmake -B build -DOpenCV_DIR=/path/to/opencv4
cmake --build build

### Migration Script

```bash
#!/bin/bash
# migrate_opencv4.sh

echo "Removing OpenCV 3.x compatibility code..."

# Find and remove OPENCV3_COMPAT defines
grep -r "OPENCV3_COMPAT" --include="*.cpp" --include="*.h" --include="*.hpp" . | \
    grep -v "Binary" | \
    while read -r line; do
        file=$(echo $line | cut -d: -f1)
        echo "Processing: $file"
        
        # Remove #ifdef OPENCV3_COMPAT blocks
        # Note: This is a simplified example - use with caution
    done

echo "Done. Manual review required for complex conditionals."

Testing

// tests/opencv4_api_test.cpp

#include <gtest/gtest.h>
#include <opencv2/opencv.hpp>

TEST(OpencvAPI, ImreadFlags) {
    // Verify OpenCV 4 API is used
    cv::Mat img = cv::imread("test.jpg", cv::IMREAD_COLOR);
    EXPECT_FALSE(img.empty());
}

TEST(OpencvAPI, ColorConversion) {
    cv::Mat bgr(100, 100, CV_8UC3);
    cv::Mat gray;
    
    // OpenCV 4 constant
    cv::cvtColor(bgr, gray, cv::COLOR_BGR2GRAY);
    
    EXPECT_EQ(gray.channels(), 1);
}

TEST(OpencvAPI, VideoCapture) {
    // OpenCV 4 API
    cv::VideoCapture cap;
    EXPECT_TRUE(cap.set(cv::CAP_PROP_FRAME_WIDTH, 640));
    EXPECT_TRUE(cap.set(cv::CAP_PROP_FRAME_HEIGHT, 480));
}

int main(int argc, char** argv) {
    ::testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}

CI/CD Updates

# .github/workflows/ci.yml

- name: Install OpenCV
  run: |
    # Ubuntu
    if [[ "$RUNNER_OS" == "Linux" ]]; then
      sudo apt-get update
      sudo apt-get install -y libopencv-dev
    fi
    
    # Verify version
    pkg-config --modversion opencv4

- name: Configure
  run: |
    cmake -B build \
      -DOpenCV_DIR=/usr/lib/x86_64-linux-gnu/cmake/opencv4

- name: Build
  run: cmake --build build --parallel

Benefits of Migration

1. Simplified code - No conditional compilation blocks
2. Better performance - OpenCV 4 has SIMD optimizations
3. Modern C++ - Uses C++11/14/17 features
4. Reduced maintenance - Single code path to maintain
5. Better error messages - OpenCV 4 has improved error handling
6. Security - OpenCV 3 is no longer receiving updates

Breaking Changes Note

This change is NOT backward compatible. Projects using:

• Ubuntu 18.04 with OpenCV 3.2
• Custom OpenCV 3 builds

Will need to upgrade to OpenCV 4.0+ before using new rocAL versions.

Files to Modify Summary

File	Change
CMakeLists.txt	Update find_package version requirement
include/*.h	Remove legacy API constants
src/decoders/**/*.cpp	Use cv::IMREAD_* and cv::COLOR_*
tests/	Update to OpenCV 4 API
README.md	Update dependency documentation
CMakeModules/FindOpenCV.cmake	Remove if custom, use system