OpenCV & OpenGL

OpenGL OpenGL: Basic Coding
1

Hi. How can I project the model created by OpenGL to the image loaded by OpenCV?

I used OpenCV to load an image (IplImage *src = cvLoadImage(argv[1]),and separately I used OpenGL to create a model. But I want to project the model I created to that image and then do some other tasks by using OpenCV. I am a very beginner for both OpenGL and OpenCV. If anybody knows how to do it,please help me. Thank you.

2

If you don’t need to do this task several times per frame, you could use glReadPixels. This reads your window (or a portion, whatever you ask for it) onto an off-screen buffer. I suppose you could then load this buffer into OpenCV. Remember to check the image storage type, such as byte, etc.

3

Thanks for your help. But I have to do that task many times per frame. Namely, I have to adjust the model -> project to the image -> do some Image processing process -> adjust the model -> project -> and so on. I have to do these process several times. Do you know how I can do it efficiently? Thank you.

4

Hi there!!

See, I am using OpenCV to process images captured form a webcam. But, I want to make drawings in this images with OpenGL. So, I found this functions, glDrawPixels and glReadPixels, that should help me getting my OpenCV image from and to OpenCV. But they are not working as I expected them to work.

I tried this simple code, I would like anyone to tell me what’s wrong:

glDrawPixels(320,240,GL_RGBA,GL_UNSIGNED_BYTE,dataPtr);

glClearColor (0.0, 0.0, 0.0, 0.0);
glClear (GL_COLOR_BUFFER_BIT);
glColor3f (1.0, 1.0, 1.0);
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
glBegin(GL_POLYGON);
glVertex3f (0.25, 0.25, 0.0);
glVertex3f (0.75, 0.25, 0.0);
glVertex3f (0.75, 0.75, 0.0);
glVertex3f (0.25, 0.75, 0.0);
glEnd();
glFlush();

glReadPixels(0,0,320,240,GL_RGBA,GL_UNSIGNED_BYTE,dataPtr);

Are there any other ways to achive the same thing?

I’d appreciate any help. Thanks in advance.

5

Hi there! :slight_smile:

I finally made it, I have the OpenCV image in an OpenGL window. That’s not what I wanted, but that’s the best I can get. I didn’t use GLUT, as GLUT has its own mainloop, so I used freeGLUT instead. Here is the code.
Initializing function:

int init(void)
{
//general initialization:
	char cadena[25]="GestionMarcaAR\0";
	char **argv;
	int argc = 1;

	argv=(char **)malloc(sizeof(char *));
	*argv=(char *)malloc(sizeof(char)*10);
	strcpy(*argv, cadena);

	glutInit(&argc,argv); //we cheat it ;P

	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
	glutInitWindowPosition(800, 400);
	glutInitWindowSize(320,240);
	glutCreateWindow("Name");

	glutDisplayFunc(draw);
	glutIdleFunc(draw);

//initializating the texture mapping
	GLuint mTexture;
	glGenTextures(1, &mTexture);
	glBindTexture(GL_TEXTURE_2D, mTexture);
	glEnable(GL_TEXTURE_2D);
	glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);	
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

	
	glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

	glClearColor(1.0f, 1.0f, 1.0f, 1.0f); //color blanco de fondo
	glColor3f(0.0f,0.0f,0.0f);

	return 0;
}

Drawing function:

void draw()
{
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB,320,240,0,GL_BGR,GL_UNSIGNED_BYTE, imagen->imageData);
	
	glBegin(GL_POLYGON);
		glTexCoord2f(0.0f, 0.0f); glVertex2f(-1.0f, -1.0f);
		glTexCoord2f(1.0f, 0.0f); glVertex2f( 1.0f, -1.0f);
		glTexCoord2f(1.0f, 1.0f); glVertex2f( 1.0f,  1.0f);
		glTexCoord2f(0.0f, 1.0f); glVertex2f(-1.0f,  1.0f);
	glEnd();
	
	glFlush();
	
	glutSwapBuffers();
}

And what is needed to be anywhere in the mainloop of openCV:

glutPostRedisplay();
glutMainLoopEvent();   //freeglut function