Loading Images (using their RGB(A) pixel data) in openGL textures - c++

Question

In the main function:
img = cvLoadImage("test.JPG");
//openCV functions to load and create matrix
CvMat *mat = cvCreateMat(img->height,img->width,CV_8SC3 );
cvGetMat( img, mat,0,1);
//creating the 3-dimensional array during runtime
data = new float**[img->height];
for(int i=0;i<img->height;i++){
data[i] = new float*[img->width];
}
for(int i=0;i<img->height;i++){
for(int j=0;j<img->width;j++)
data[i][j] = new float[3];
}
//setting RGB values
for(int i=0;i<img->height;i++)
{
for(int j=0;j<img->width;j++)
{
CvScalar scal = cvGet2D( mat,i,j);
data[i][j][0] = scal.val[0];
data[i][j][1] = scal.val[1];
data[i][j][2] = scal.val[2];
}
}
I am using openCV to get the image pixel data, storing it in the dynamically created matrix "data".Now generating textures and binding them:
glGenTextures(1,&texName);
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);
glTexEnvf(GL_TEXTURE_ENV,GL_TEXTURE_ENV_MODE,GL_MODULATE);
glTexImage2D(GL_TEXTURE_2D, 0 ,GL_RGB, img->width,img->height,0,GL_RGB,GL_FLOAT,data);
glBindTexture(GL_TEXTURE_2D, texName);
glBegin(GL_QUADS);
glTexCoord2f(0,0);
glVertex3f(-1,-1,0);
glTexCoord2f(0,1);
glVertex3f(-1,1,0);
glTexCoord2f(1,1);
glVertex3f(1,1,0);
glTexCoord2f(1,0);
glVertex3f(1,-1,0);
glEnd();
There are no compilation errors but during the runtime, the window displays the square I made, but not the image that I tried to convert into texture.
How do I achieve loading any image into texture using the pixel data that I extract using openCV. I have printed the RGB values and they seem legit enough and the number of triplets printed are as expected.

Answer 1

glBindTexture should be called before the glTexParemeteri...glTexImage2D calls, so openGL knows which texture you're setting up.
glEnable(GL_TEXTURE_2D);
glGenTextures(1,&texName);
glBindTexture(GL_TEXTURE_2D, texName);
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);
glTexEnvf(GL_TEXTURE_ENV,GL_TEXTURE_ENV_MODE,GL_MODULATE);
glTexImage2D(GL_TEXTURE_2D, 0 ,GL_RGB, img->width,img->height,0,GL_RGB,GL_FLOAT,data);
More importantly, you are not setting up your data variable correctly:
float* data = new float[img->height * img->width * 3];
for (int i = 0; i < img->height; i++)
{
for (int j = 0; j < img->width; j++)
{
CvScalar scal = cvGet2D(mat, i, j);
data[(i * img->width + j) + 0] = scal.val[0];
data[(i * img->width + j) + 1] = scal.val[1];
data[(i * img->width + j) + 2] = scal.val[2];
}
}
Also, you might need to swap the order of color components and/or convert them to 0..1 range, I don't know how openCV loads images.