OpenGL interoperability

opengl_interop

asked 2013-03-21 08:23:14 -0600

F_Michele
31 ●1 ●1 ●5

Hello all!

I'm under Linux and compiled OpenCV 2.4.4 with OpenGL support, but I don't have any idea of how using the opengl_interop.hpp functions (some of them are even undocumented!, at least on my version of documentation). Looking at window.cpp in the section with OpenGL enabled I found some hints about the use of the functions setOpenGLContext, setOpenGLDrawCallback and updateView but I can't get working even this very simple piece of code:

#include <opencv2/opencv.hpp>
#include <GL/gl.h>
#include <GL/glut.h>
#include <opencv2/core/opengl_interop.hpp>

using namespace cv;

void on_opengl(void* userdata);

int main(void)
{
    VideoCapture webcam(CV_CAP_ANY);
    Mat frame;
    namedWindow("window", CV_WINDOW_OPENGL);
    setOpenGlContext("window");
    while(waitKey(30) < 0)
    {
        webcam >> frame;
        setOpenGlDrawCallback("window", on_opengl);
        imshow("window", frame);
        updateWindow("window");
    }

    return 0;
}

void on_opengl(void* userdata)
{
    glLoadIdentity();

    glTranslated(0.0, 0.0, 1.0);

    glRotatef( 55, 1, 0, 0 );
    glRotatef( 45, 0, 1, 0 );
    glRotatef( 0, 0, 0, 1 );

    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();
    }
}

What is the right way of using opengl on the webcam stream? bye!

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what's the outcome of it ? btw, i think, you need to setOpenGlDrawCallback("window", on_opengl); only once

berak ( 2013-03-21 08:36:57 -0600 )edit

@berak: the outcome is that just the webcam image is displayed. I put setOpenGLDrawCallback in the loop because every time that imshow is called when the OpenGL support is present it resets the drawCallback to a commodity function in order to show the image as a texture.

F_Michele ( 2013-03-21 08:47:02 -0600 )edit

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3 answers

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answered 2013-03-21 11:03:57 -0600

Vladislav Vinogradov

4775 ●4 ●24 ●62

Do not call imshow if you use your own draw callback:

void on_opengl(void* userdata);

int main(void)
{
    VideoCapture webcam(CV_CAP_ANY);

    namedWindow("window", CV_WINDOW_OPENGL);

    Mat frame;
    ogl::Texture2D tex;

    setOpenGlDrawCallback("window", on_opengl, &tex);

    while(waitKey(30) < 0)
    {
        webcam >> frame;
        tex.copyFrom(frame);
        updateWindow("window");
    }

    setOpenGlDrawCallback("window", 0, 0);
    destroyAllWindows();

    return 0;
}

void on_opengl(void* userdata)
{
    ogl::Texture2D* pTex = static_cast<ogl::Texture2D*>(userdata);
    if (pTex->empty())
        return;

    glLoadIdentity();

    glTranslated(0.0, 0.0, 1.0);

    glRotatef( 55, 1, 0, 0 );
    glRotatef( 45, 0, 1, 0 );
    glRotatef( 0, 0, 0, 1 );

    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 } }
    };

    glEnable(GL_TEXTURE_2D);
    pTex->bind();

    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();
    }
}

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answered 2014-08-06 09:11:50 -0600

protonmesh
70 ●2 ●4

In the draw callback, consider the use of: C++: void ogl::render(const Texture2D& tex, Rect_<double> wndRect=Rect_<double>(0.0, 0.0, 1.0, 1.0), Rect_<double> texRect=Rect_<double>(0.0, 0.0, 1.0, 1.0))

which encapsulates the GL commands necessary to display a texture mapped to a rectangle in the screen plane.

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-1

answered 2013-03-21 16:11:17 -0600

PhantomFav
11 ●1 ●2

updated 2013-03-21 16:31:46 -0600

You must simply use opengGL with openCV and not viceversa. You can build your shape in openGL and apply the texture using the tools that opencv come with. For example this is a function to transform a IplImage into a texture for openGL:

GLuint ConvertIplToTexture(IplImage *image){
    GLuint texture;
    glGenTextures(1,&texture);
    glBindTexture(GL_TEXTURE_2D,texture);
    gluBuild2DMipmaps(GL_TEXTURE_2D,3,image->width,image->height,
                             GL_BGR,GL_UNSIGNED_BYTE,image->imageData);
    return texture;
}

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I don't think that's true, right? I mean why is there a CV_WINDOW_OPENGL and opengl_interop.hpp that specifically allows you to use opencv with opengl (and not viceversa)?

Elador ( 2013-07-29 17:50:34 -0600 )edit

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