main.cpp

//I wrote this following a tutorial onliine
//The date is 19th April, 2021
//it is still a work in progress

//window was previously popping up
// but now flashes up and disappears

#include <glad/glad.h>
#include <GLFW/glfw3.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
using namespace std;

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}


//*****************************************************************
//*************************************************************

PFNGLGETSTRINGPROC glad_glGetString = NULL;
PFNGLVIEWPORTPROC glad_glViewport = NULL;

static int max_loaded_major;
static int max_loaded_minor;

static const char *exts = NULL;
static int num_exts_i = 0;
static char **exts_i = NULL;

struct gladGLversionStruct GLVersion = { 0, 0 };

static void free_exts(void) {
    if (exts_i != NULL) {
        int index;
        for(index = 0; index < num_exts_i; index++) {
            free((char *)exts_i[index]);
        }
        free((void *)exts_i);
        exts_i = NULL;
    }
}

static int has_ext(const char *ext) {
#ifdef _GLAD_IS_SOME_NEW_VERSION
    if(max_loaded_major < 3) {
#endif
        const char *extensions;
        const char *loc;
        const char *terminator;
        extensions = exts;
        if(extensions == NULL || ext == NULL) {
            return 0;
        }

        while(1) {
            loc = strstr(extensions, ext);
            if(loc == NULL) {
                return 0;
            }

            terminator = loc + strlen(ext);
            if((loc == extensions || *(loc - 1) == ' ') &&
                (*terminator == ' ' || *terminator == '\0')) {
                return 1;
            }
            extensions = terminator;
        }
#ifdef _GLAD_IS_SOME_NEW_VERSION
    } else {
        int index;
        if(exts_i == NULL) return 0;
        for(index = 0; index < num_exts_i; index++) {
            const char *e = exts_i[index];

            if(exts_i[index] != NULL && strcmp(e, ext) == 0) {
                return 1;
            }
        }
    }
#endif

    return 0;
}


static int get_exts(void) {
#ifdef _GLAD_IS_SOME_NEW_VERSION
    if(max_loaded_major < 3) {
#endif
        exts = (const char *)glGetString(GL_EXTENSIONS);
#ifdef _GLAD_IS_SOME_NEW_VERSION
    } else {
        unsigned int index;

        num_exts_i = 0;
        glGetIntegerv(GL_NUM_EXTENSIONS, &num_exts_i);
        if (num_exts_i > 0) {
            exts_i = (char **)malloc((size_t)num_exts_i * (sizeof *exts_i));
        }

        if (exts_i == NULL) {
            return 0;
        }

        for(index = 0; index < (unsigned)num_exts_i; index++) {
            const char *gl_str_tmp = (const char*)glGetStringi(GL_EXTENSIONS, index);
            size_t len = strlen(gl_str_tmp);

            char *local_str = (char*)malloc((len+1) * sizeof(char));
            if(local_str != NULL) {
                memcpy(local_str, gl_str_tmp, (len+1) * sizeof(char));
            }
            exts_i[index] = local_str;
        }
    }
#endif
    return 1;
}


static int find_extensionsGL(void) {
	if (!get_exts()) return 0;
	(void)&has_ext;
	free_exts();
	return 1;

}


int gladLoadGLLoader(GLADloadproc load) {
	GLVersion.major = 0; GLVersion.minor = 0;
	glGetString = (PFNGLGETSTRINGPROC)load("glGetString");
	if(glGetString == NULL) return 0;
	if(glGetString(GL_VERSION) == NULL) return 0;
//	find_coreGL();
//	load_GL_VERSION_1_0(load);
//	load_GL_VERSION_1_1(load);
//	load_GL_VERSION_1_2(load);
//	load_GL_VERSION_1_3(load);
//	load_GL_VERSION_1_4(load);
//	load_GL_VERSION_1_5(load);
//	load_GL_VERSION_2_0(load);
//	load_GL_VERSION_2_1(load);
//	load_GL_VERSION_3_0(load);
//	load_GL_VERSION_3_1(load);
//	load_GL_VERSION_3_2(load);
//	load_GL_VERSION_3_3(load);
//	load_GL_VERSION_4_0(load);
//	load_GL_VERSION_4_1(load);
//	load_GL_VERSION_4_2(load);
//	load_GL_VERSION_4_3(load);
//	load_GL_VERSION_4_4(load);
//	load_GL_VERSION_4_5(load);
//	load_GL_VERSION_4_6(load);

	if (!find_extensionsGL()) return 0;
	return GLVersion.major != 0 || GLVersion.minor != 0;
}