Add current project. Compiles and runs on raspberry pi. Doesn't on ubuntu box (mismatch of opencv versions)

.gitignore

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+build
+bin
+cmake-modules

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.1)
+PROJECT (opencv_fb)
+
+set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${CMAKE_CURRENT_SOURCE_DIR}/cmake-modules)
+
+find_package(OpenCV HINTS /usr/local/opt/opencv /usr/local/Cellar/opencv REQUIRED)
+
+set( NAME_SRC
+    opencv_fb.cpp    
+)
+
+INCLUDE_DIRECTORIES( ${CMAKE_CURRENT_SOURCE_DIR}/include )
+link_directories( ${CMAKE_BINARY_DIR}/bin)
+set(EXECUTABLE_OUTPUT_PATH ${CMAKE_BINARY_DIR}/bin)
+add_executable( opencv_fb ${NAME_SRC} ${NAME_HEADERS} )
+
+target_link_libraries( opencv_fb ${OpenCV_LIBS} )

compile.sh

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+#!/bin/bash
+
+#mkdir -p bin
+#g++ -o bin/opencv_fb -lopencv_core -lopencv_highgui -lopencv_imgproc opencv_fb.cpp
+
+mkdir -p build
+cd build
+cmake ..
+make -j

opencv_fb.cpp

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+/**
+ * @file opencv_fb.cpp
+ * Displays OpenCV video on framebuffer.
+ * Compile with
+ * g++ -o fbwrite_video -lopencv_core -lopencv_highgui -lopencv_imgproc fbwrite_video.cpp
+ *
+ * Contains code from https://stackoverflow.com/questions/4722301/writing-to-frame-buffer
+ */
+
+#include <iostream> // for cerr
+#include <opencv2/imgproc/imgproc.hpp>  // for cvtColor
+#include <opencv2/highgui/highgui.hpp> // for VideoCapture
+#include <fstream> // for ofstream
+#include <boost/timer/timer.hpp> // for boost::timer::cpu_timer
+
+using namespace std;
+using namespace cv;
+
+// this is C :/
+#include <stdint.h> // for uint32_t
+#include <sys/ioctl.h> // for ioctl
+#include <linux/fb.h> // for fb_
+#include <fcntl.h> // for O_RDWR
+
+struct framebuffer_info { 
+    uint32_t bits_per_pixel;
+    uint32_t xres_virtual;
+    uint32_t yres_virtual;
+};
+
+struct framebuffer_info get_framebuffer_info(const char* framebuffer_device_path) {
+    struct framebuffer_info info;
+    struct fb_var_screeninfo screen_info;
+    int fd = -1;
+    fd = open(framebuffer_device_path, O_RDWR);
+    if (fd >= 0) {
+        if (!ioctl(fd, FBIOGET_VSCREENINFO, &screen_info)) {
+            info.xres_virtual = screen_info.xres_virtual;
+            info.yres_virtual = screen_info.yres_virtual;
+            info.bits_per_pixel = screen_info.bits_per_pixel;
+        }
+    }
+    return info;
+};
+// C ends here
+
+void display (Mat frame, framebuffer_info fb_info, ofstream& ofs) {
+    if (frame.depth() != CV_8U) {
+        cerr << "Not 8 bits per pixel and channel." << endl;
+    } else if (frame.channels() != 3) {
+        cerr << "Not 3 channels." << endl;
+    } else {
+        // 3 Channels (assumed BGR), 8 Bit per Pixel and Channel
+        int framebuffer_width = fb_info.xres_virtual;
+        int framebuffer_depth = fb_info.bits_per_pixel;
+        Size2f frame_size = frame.size();
+        Mat framebuffer_compat;
+        switch (framebuffer_depth) {
+            case 16:
+                cvtColor(frame, framebuffer_compat, COLOR_BGR2BGR565);
+                for (int y = 0; y < frame_size.height ; y++) {
+                    ofs.seekp(y*framebuffer_width*2);
+                    ofs.write(reinterpret_cast<char*>(framebuffer_compat.ptr(y)),frame_size.width*2);
+                }
+            break;
+            case 32: {
+                    vector<Mat> split_bgr;
+                    split(frame, split_bgr);
+                    split_bgr.push_back(Mat(frame_size,CV_8UC1,Scalar(255)));
+                    merge(split_bgr, framebuffer_compat);
+                    for (int y = 0; y < frame_size.height ; y++) {
+                        ofs.seekp(y*framebuffer_width*4);
+                        ofs.write(reinterpret_cast<char*>(framebuffer_compat.ptr(y)),frame_size.width*4);
+                    }
+                } break;
+            default:
+                cerr << "Unsupported depth of framebuffer." << endl;
+        }
+    }
+}
+
+Mat frameEffects (Mat frame) {
+    Mat grey;
+    Mat contrast;
+    Mat blur;
+    Mat flipper;
+    //flip(frame, flipper, 1);
+    //cvtColor(flipper, grey, COLOR_BGR2GRAY);
+    //grey.convertTo(contrast, -1, 1, 0);
+    //cvtColor(contrast, frame, COLOR_GRAY2BGR);
+    return frame;
+}
+
+int main(int, char**) {
+    const int frame_rate = 24;
+    int frameCount = 0;
+    framebuffer_info fb_info = get_framebuffer_info("/dev/fb0");
+    VideoCapture cap(0);
+    if(!cap.isOpened()) {
+        cerr << "Could not open video device." << endl;
+        return 1;
+    } else {
+        cout << "Successfully opened video device." << endl;
+        cap.set(CAP_PROP_FRAME_WIDTH, 1280);
+        cap.set(CAP_PROP_FRAME_HEIGHT, 720);
+        cap.set(CAP_PROP_FPS, frame_rate);
+        //cap.set(CAP_PROP_BUFFERSIZE,3);
+        cout << cap.get(CAP_PROP_FRAME_WIDTH) << "x" << cap.get(CAP_PROP_FRAME_HEIGHT) << endl;
+        ofstream ofs("/dev/fb0");
+        Mat frame;
+        Mat displayFrame;
+        while (true) {
+            cap >> frame;
+            frame = frameEffects(frame);
+            resize(frame, displayFrame, Size(fb_info.xres_virtual, fb_info.yres_virtual), 2, 2, INTER_CUBIC);
+            display(displayFrame, fb_info, ofs);
+            waitKey(42);
+        }
+    }
+}