I'm working on an AR program.

please heip me dealing's almost done.

I found marker and rvec,tvec by SolvePnP.

I can not draw object in OpenGL.

I am beginer OpenGL,OpenCV.

I want to render 3D cube over that marker using OpenGL.

use support opengl mode by build opencv.

    int main(int argc, char* argv[])
{
    ....
    namedWindow(winname, CV_WINDOW_OPENGL);
    setOpenGlDrawCallback(winname.c_str(), on_opengl);
    .....
        find marker

According to "http://answers.opencv.org/question/23089/opencv-opengl-proper-camera-pose-using-solvepnp/" I'm doing it like this:

Mat rotation(4, 4, CV_64F);
                        Mat viewMatrix = cv::Mat::zeros(4, 4, CV_64FC1);
                        cv::Rodrigues(rvec, rotation);

                        for (unsigned int row = 0; row<3; ++row)
                        {
                            for (unsigned int col = 0; col<3; ++col)
                            {
                                viewMatrix.at<double>(row, col) = rotation.at<double>(row, col);
                            }
                            viewMatrix.at<double>(row, 3) = tvec.at<double>(row, 0);
                        }
                        viewMatrix.at<double>(3, 3) = 1.0f;

                        cv::Mat glViewMatrix = cv::Mat::zeros(4, 4, CV_64F);
                        cv::transpose(viewMatrix, glViewMatrix);
                        glViewMatrix2 = glViewMatrix.clone();

opengl callback

    void on_opengl(void* param)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glLoadMatrixd(&glViewMatrix2.at<double>(0, 0));
    //glTranslated(glViewMatrix2.at<double>(0, 3), -glViewMatrix2.at<double>(1, 3),0);
    //glTranslated(glViewMatrix2.at<double>(3, 0), -glViewMatrix2.at<double>(3, 1), -glViewMatrix2.at<double>(3, 2));
    glTranslated(0.0, 0.0, 0.0);
    static const int coords[6][4][3] = {
        { { +1, -1, -1 },{ -1, -1, -1 },{ -1, +1, -1 },{ +1, +1, -1 } },
        { { +1, +1, -1 },{ -1, +1, -1 },{ -1, +1, +1 },{ +1, +1, +1 } },
        { { +1, -1, +1 },{ +1, -1, -1 },{ +1, +1, -1 },{ +1, +1, +1 } },
        { { -1, -1, -1 },{ -1, -1, +1 },{ -1, +1, +1 },{ -1, +1, -1 } },
        { { +1, -1, +1 },{ -1, -1, +1 },{ -1, -1, -1 },{ +1, -1, -1 } },
        { { -1, -1, +1 },{ +1, -1, +1 },{ +1, +1, +1 },{ -1, +1, +1 } }
    };

    for (int i = 0; i < 6; ++i) {
        glColor3ub(i * 20, 100 + i * 10, i * 42);
        glBegin(GL_QUADS);
        for (int j = 0; j < 4; ++j) {
            glVertex3d(0.2 * coords[i][j][0], 0.2 * coords[i][j][1], 0.2 * coords[i][j][2]);
        }
        glEnd();
    }
}

i cannot find cube.

if I delete "glLoadMatrixd(&glViewMatrix2.at<double>(0, 0));" this line.

I can find cube on center.

Q2-How to use glut.where can I do"glutInit(&argc2, argv2);"

find biggest rectangle. I need to find trapezoid's 4 points I try use "Rect" but only 2points just 1point is good point help me

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

using namespace cv;
using namespace std;

int main(int argc, char** argv) {

//Mat src = imread(argv[1]);
//Mat src = imread("pic1.png");
Mat src = imread("IMG_20160708_1338252.jpg");
imshow("source", src);
int largest_area = 0;
int largest_contour_index = 0;
Rect bounding_rect;

Mat thr;
cvtColor(src, thr, COLOR_BGR2GRAY); //Convert to gray
threshold(thr, thr, 125, 255, THRESH_BINARY); //Threshold the gray

vector<vector<Point> > contours; // Vector for storing contours

findContours(thr, contours, RETR_CCOMP, CHAIN_APPROX_SIMPLE); // Find the contours in the image

for (size_t i = 0; i < contours.size(); i++) // iterate through each contour.
{
    double area = contourArea(contours[i]);  //  Find the area of contour
    //src면적이랑 area가 같으면 제외 
    //if (src.size().area != area) {
        if (area > largest_area)
        {
            largest_area = area;
            largest_contour_index = i;               //Store the index of largest contour
            bounding_rect = boundingRect(contours[i]); // Find the bounding rectangle for biggest contour
        }
    //}
}

printf("top%d,%d\n", bounding_rect.tl().x, bounding_rect.tl().y);
printf("bottom%d,%d\n\n", bounding_rect.br().x, bounding_rect.br().y);
printf("top%d,%d\n", bounding_rect.x, bounding_rect.y);
printf("%d,%d\n", bounding_rect.x, bounding_rect.y+ bounding_rect.height);
printf("bottom%d,%d\n", bounding_rect.x + bounding_rect.width, bounding_rect.y);
printf("%d,%d\n\n", bounding_rect.x+ bounding_rect.width, bounding_rect.y+ bounding_rect.height);

//printf("bottom%d,%d\n", bounding_rect.br().x, bounding_rect.br().y);
//contours[largest_contour_index];//가장큰 사각형
//contours[largest_contour_index][0].x; contours[largest_contour_index][0].y;
printf("1-%d,", contours[largest_contour_index]);
printf("1-%d\n", contours[largest_contour_index][0].y);
printf("2-%d,", contours[largest_contour_index][1].x);
printf("2-%d\n", contours[largest_contour_index][1].y);
printf("3-%d,", contours[largest_contour_index][2].x);
printf("3-%d\n", contours[largest_contour_index][2].y);
printf("4-%d,", contours[largest_contour_index][3].x);
printf("4-%d\n", contours[largest_contour_index][3].y);

//printf("1%d,", contours[0][largest_contour_index].x);

drawContours(src, contours, largest_contour_index, Scalar(0, 255, 0), 2); // Draw the largest contour using previously stored index.

imshow("result", src);
waitKey();
return 0;

}