Fastest possible OpenCV 2 OpenGL context - performance

Question

I've been searching through the net for a few day looking for the fastest possible way to take a OpenCV webcam capture and display it on an OpenGL context. So far this seems to work OK until I need to zoom.
void Camera::DrawIplImage1(IplImage *image, int x, int y, GLfloat xZoom, GLfloat yZoom)
{
GLenum format;
switch(image->nChannels) {
case 1:
format = GL_LUMINANCE;
break;
case 2:
format = GL_LUMINANCE_ALPHA;
break;
case 3:
format = GL_BGR;
break;
default:
return;
}
yZoom =- yZoom;
glRasterPos2i(x, y);
glPixelZoom(xZoom, yZoom); //Slow when not (1.0f, 1.0f);
glDrawPixels(image->width, image->height, format, GL_UNSIGNED_BYTE, image->imageData);
}
I've heard that maybe taking the FBO approach would be even faster. Any ideas out there on the fastest possible way to get an OpenCV webcam capture to an OpenGL context. I will test everything I see and post results.

Answer 1

Are you sure your openGL implementation needs ^2 textures? Even very poor PC implementations (yes Intel) can manage arbitrary sizes now.
Then the quickest is probably to use a openGL Pixel buffer
Sorry the code is from Qt, so the function names are slightly different but the sequence is the same
Allocate the opengl Texture
glEnable(GL_TEXTURE_2D);
glGenTextures(1,&texture);
glBindTexture(GL_TEXTURE_2D,texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, glFormat, width, height, 0, glFormatExt, glType, NULL );
glDisable(GL_TEXTURE_2D);
Now get a pointer to the texture to use the memeory
glbuffer.bind();
unsigned char *dest = (unsigned char*)glbuffer.map(QGLBuffer::ReadWrite);
// creates an openCV image but the pixel data is stored in an opengl buffer
cv::Mat opencvImage(rows,cols,CV_TYPE,dest);
.... do stuff ....
glbuffer.unmap(); // pointer is no longer valid - so neither is openCV image
Then to draw it - this should be essentially instant because the data was copied to the GPU in the mapped calls above
glBindTexture(GL_TEXTURE_2D,texture);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0,0, width, height, glFormatExt, glType, 0);
glbuffer.release();
By using different types for glFormat and glFormatExt you can have the graphics card automatically convert between opencVs BGR and typical RGBA display formats for you in hardware.