OpenGL Texture Mapping

If you are doing AR, and for texture mapping

use glTexImage2D and glTexSubImage2D

For the glTexImage2D to work, the SIZE OF IMAGE MUST be POWER of 2, e,g, 2, 4 , 8, 16

any size like 640 x 480 is unaccepatable since it is not power of 2.

void initTexture()
{
//Alloc Texture
	IplImage* frameImg = cvQueryFrame(capture);
	IplImage *textImg = cvCreateImage(cvSize(512,256), frameImg->depth, frameImg->nChannels);
	cvResize(frameImg, textImg);
	cvFlip(textImg, NULL, 0);

	glGenTextures(1, &textureID);
	glBindTexture(GL_TEXTURE_2D, textureID);
	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);
	glTexImage2D(GL_TEXTURE_2D, 0, 3,textImg->width, textImg->height,0,
		GL_BGR_EXT,GL_UNSIGNED_BYTE, textImg->imageData);

	cvReleaseImage(&textImg);

}

After the initialization of the textureMap, one can proceed to draw it using glTexSubImage2D

void drawCameraImage(IplImage*  tempImage)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) ;


	//////////////////////////////////////////////////////////////////////////////////
	// Do texture mapping for drawing image in OpenGL space

	glViewport(0,0, GL_WINDOW_WIDTH, GL_WINDOW_HEIGHT) ;

	glMatrixMode(GL_PROJECTION) ;
	glLoadIdentity() ;
	glOrtho(0, GL_WINDOW_WIDTH, 0, GL_WINDOW_HEIGHT, 0, 2000) ;

	glMatrixMode(GL_MODELVIEW) ;
	glLoadIdentity() ;

	glEnable(GL_TEXTURE_2D) ;
	glBindTexture(GL_TEXTURE_2D, textureID) ;
	LoadCameraImage(tempImage);
	glBegin(GL_QUADS) ;
		glTexCoord2f(0,0) ;
		glVertex3f(0,0, -1999) ;

		glTexCoord2f(1,0) ;
		glVertex3f(GL_WINDOW_WIDTH,0, -1999) ;

		glTexCoord2f(1,1) ;
		glVertex3f(GL_WINDOW_WIDTH,GL_WINDOW_HEIGHT, -1999) ;

		glTexCoord2f(0,1) ;
		glVertex3f(0,GL_WINDOW_HEIGHT, -1999) ;
	glEnd() ;

	glDisable(GL_TEXTURE_2D) ;

}

void LoadCameraImage(IplImage*  tempImage) 
{
	
	
	cvFlip(tempImage, NULL, 0);
	IplImage *scaledImage = cvCreateImage(cvSize(512, 256),  tempImage->depth, tempImage->nChannels);
	cvResize(tempImage, scaledImage, CV_INTER_AREA);
	
	glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);

	glTexSubImage2D(GL_TEXTURE_2D, 0, 0,0, scaledImage->width, scaledImage->height, GL_BGR_EXT,
		GL_UNSIGNED_BYTE, scaledImage->imageData);
	
	cvReleaseImage(&scaledImage) ;
}

glTexSubImage2D is only effective after glTexImage2D is called, so remember to use glTexImage2D

SubImage function is faster than calling glTexImage2D again and again.

To learn more about openGL programming, you might want to read the following list of books: