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View Full Version : Problems using OpenGL with OpenCV



tsoemod
07-27-2016, 09:29 AM
Hi!

I'm pretty new to OpenGL and currently just testing to see if I can get some basic things to work, but I've run into some issues. In my program I am trying to load an image into a matrix type using OpenCV 3.1's imread(), convert it to a texture with a texture_id handle using glTexImage2D(), and pass the handle to another function which converts it back to a matrix type using glGetTexImage().

My problem is that the data attached to the texture_id somehow returns to NULL at the read by glGetTexImage(). I have tried to implement the context for the OpenCV functions, but i don't know if it is correct. There may also be other faults to my code, that I have not considered. Any help would be appreciated! I am writing in C++11 using VisualStudio15, OpenCV3.1, OpenGL4.4, GLFW and GLEW.

The CPP file:


#include "Texture.h"

GLuint matToTexture(Mat image) {

GLuint texture_id;

if (image.empty()) {
cout << "Image empty." << endl;
}

else {

glGenTextures(1, &texture_id);
glBindTexture(GL_TEXTURE_2D, texture_id);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

glTexImage2D(GL_TEXTURE_2D,
0,
GL_RGB,
image.cols,
image.rows,
0,
GL_BGR,
GL_UNSIGNED_BYTE,
image.ptr());

}
return texture_id;
}

Mat textureToMat(GLuint texture_id) {

glBindTexture(GL_TEXTURE_2D, texture_id);
GLenum texture_width, texture_height;
//GLenum texture_format;

glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, (GLint*)&texture_width);
glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, (GLint*)&texture_height);
//glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_INTERNAL_FORMAT, (GLint*)&texture_format);

unsigned char* texture_bytes = (unsigned char*)malloc(sizeof(unsigned char)*texture_width*texture_height * 3);

glGetTexImage(GL_TEXTURE_2D, 0, GL_BGR, GL_UNSIGNED_BYTE, texture_bytes);

Mat out = Mat(texture_height, texture_width, CV_8UC3, texture_bytes);

//Mat out = Mat(texture_height, texture_width, CV_8UC3, texture_bytes).clone();

return out;

}

The header file:



#ifndef TEXTURE_H
#define TEXTURE_H

#include "glew.h"
#include "glfw3.h"

#include <string>
#include <iostream>
#include <vector>
#include <opencv\highgui.h>
#include <opencv\cv.h>
#include <opencv2\opencv.hpp>

using namespace std;
using namespace cv;

Mat textureToMat(GLuint textureID);
GLuint matToTexture(Mat image);

#endif /*!TEXTURE_H*/

The main call:


#include "glew.h"
#include "glfw3.h"
#include "Texture.h"

using namespace std;

int main(){

glfwInit();
glewExperimental = GL_TRUE;
glewInit();

glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);

GLFWwindow* offscreen_context = glfwCreateWindow(630, 354, "OpenGL", NULL, NULL);
glfwMakeContextCurrent(offscreen_context);

Mat dummy = imread("mini.jpg", CV_LOAD_IMAGE_COLOR);

GLuint tex = matToTexture(dummy);

glBindTexture(GL_TEXTURE_2D, tex);

Mat some = textureToMat(tex);

while (!glfwWindowShouldClose(offscreen_context)) {

glfwSwapBuffers(offscreen_context);
glfwPollEvents();

if (glfwGetKey(offscreen_context, GLFW_KEY_ESCAPE) == GLFW_PRESS) {
glfwSetWindowShouldClose(offscreen_context, GL_TRUE);
}
}

glfwTerminate();

return 0;

}