Loading texture for OpenGL with OpenCV - c++

Question

I have seen many code samples for loading textures for OpenGL, many of them a bit complicated to understand or requiring new functions with a lot of code.
I was thinking that as OpenCV allows us to load any image format it can be a simple an efficient way to load textures to OpenGL, but I am missing something. I have this piece of code in c++:
cv::Mat texture_cv;
GLuint texture[1];
int Status=FALSE;
if( texture_cv = imread("stones.jpg")) {
Status=TRUE; // Set The Status To TRUE
glGenTextures(1, &texture[0]); // Create The Texture
glBindTexture(GL_TEXTURE_2D, texture[0]);
glTexParameterf(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S , GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );
glTexImage2D(GL_TEXTURE_2D, 0, 3, texture_cv.cols, texture_cv.rows, 0, GL_RGB, GL_UNSIGNED_BYTE, texture_cv.data);
}
And it is not compiling because of this error:
error C2451: conditional expression of type 'cv::Mat' is illegal
Any suggestions? How should I do the conversion from cv::Mat to openGL texture?

Answer 1

Your error appears there, right?
if( texture_cv = imread("stones.jpg")) {
because in if(expr) expr must be bool or can be casted to bool. But there is no way to convert cv::Mat into boolean implicitly. But you can check the result of imread like that:
texture_cv = imread("stones.jpg");
if (texture_cv.empty()) {
// handle was an error
} else {
// do right job
}
See: cv::Mat::empty(), cv::imread
Hope that helped you.

Answer 2

The assignment operator
texture_cv = imread("stones.jpg")
returns a cv::Mat that can't be used in a conditional expression. You should write something like
if((texture_cv = imread("stones.jpg")) != /* insert condition here */ ) {
//...
}
or
texture = imread("stone.jpg");
if(!texture.empty()) {
//...
}

Answer 3

from this doc, I suggest you to change your test:
texture_cv = imread("stones.jpg");
if (texture_cv.data != NULL) {
...

Answer 4

Another short question...
I think you may need to use
glTexImage2D(GL_TEXTURE_2D, 0, 3, texture_cv.cols, texture_cv.rows, 0, GL_RGB, GL_UNSIGNED_BYTE, texture_cv.ptr());
instead of
glTexImage2D(GL_TEXTURE_2D, 0, 3, texture_cv.cols, texture_cv.rows, 0, GL_RGB, GL_UNSIGNED_BYTE, texture_cv.data);