openCV (openGL support) display usage

C++
,
1

Is there any minimal example of displaying and image , rectangle , text using :

cv::namedWindow(DISPLAY_WINDOW_NAME, cv::WINDOW_OPENGL);

I was able to display an image using this callback function :

void on_image_update_clbk(void* param) {

	/*draw image */
	cv::ogl::Texture2D* backgroundTex = (cv::ogl::Texture2D*)param;
	glEnable(GL_TEXTURE_2D);
	backgroundTex->bind();
	cv::ogl::render(*backgroundTex);
	glDisable(GL_TEXTURE_2D);
}

but I wasn’t successful until now to draw a text and rectangle on the top of that display.

2

I don’t know OpenCV’s OpenGL facilities well enough to help here.

OpenCV’s GUI facilities are limited in general.

I don’t know if there are ways to draw OpenGL primitives into such a window/viewport on top of the texture.

you can probably imagine that drawing into the Mat with cv::putText() and cv::rectangle() is an option.

you might be better served by using something like GLUT or GLFW and issuing your own OpenGL calls, combined with turning your image into a texture of some kind. OpenCV’s OpenGL window doesn’t do much else.

1 Like
3

what did you try ?
even with plain opengl it needs an awful lot of state changes to switch from 3d to 2d mode (and back)
i remember something like:

void RGL::enter2D() 
{
    static GLint view[4];
    glGetIntegerv( GL_VIEWPORT, view );
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    gluOrtho2D( view[0], view[2], view[1], view[3] );

    glPushAttrib( GL_ALL_ATTRIB_BITS );
}


void RGL::leave2D() 
{
    glPopAttrib();
	glMatrixMode(GL_PROJECTION);
	glPopMatrix();
	glMatrixMode(GL_MODELVIEW);
}
1 Like
4

thank you. I wasn’t able to display on the top of the texture because I didn’t leave 2D!

I ended up with something like this :

void on_image_update_clbk(void* param)
{
	/*draw image */
	cv::Mat* MatPtr = (cv::Mat*)param;

	draw_image2d(MatPtr);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	glOrtho(0.0f, image_with , image_height, 0.0f, 0.0f, 1.0f);  

	/*draw line*/

	DrawLine line(cv::Point2f(0, 0), cv::Point2f(500, 500));
	draw_line(line, 5);


	std::string str = "this is some text ...";
	draw_text(str, cv::Point2f(300, 500), 3, DrawColor(0.0, 0.0, 200));

}