Question

How to write OpenGL context parameters to log file in C

Answer 1

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#include <stdio.h>
#include <string.h>
#include <time.h>
#include <stdarg.h>
#include <stdbool.h>
#include <assert.h>

static const GLint WIDTH = 800, HEIGHT = 600;
static const char OPENGL_LOG_FILE[11] = "opengl.log";

bool start_opengl_log_file() {
    FILE* file = fopen(OPENGL_LOG_FILE, "w");
    if (!file) {
        fprintf(stderr, "ERROR: could not open: %s\n", OPENGL_LOG_FILE);
        return false;
    }
    time_t now = time(NULL);
    char* date = ctime(&now);
    fprintf(file, "time: %s\n", date);
    fclose(file);

    return true;
}

bool write_to_opengl_log(const char* message, ...) {
    va_list valist;
    FILE* file = fopen(OPENGL_LOG_FILE, "a");
    if (!file) {
        fprintf(stderr, "ERROR: could not open: %s\n", OPENGL_LOG_FILE);
        return false;
    }
    va_start(valist, message);
    vfprintf(file, message, valist);
    va_end(valist);
    fclose(file);

    return true;
}

bool write_error_to_opengl_log_file(const char* message, ...) {
    va_list valist;
    FILE* file = fopen(OPENGL_LOG_FILE, "a");
    if (!file) {
        fprintf(stderr, "ERROR: could not open: %s\n", OPENGL_LOG_FILE);
        return false;
    }
    va_start(valist, message);
    vfprintf(file, message, valist);
    va_end(valist);
    va_start(valist, message);
    vfprintf(stderr, message, valist);
    va_end(valist);
    fclose(file);

    return true;
}

void write_opengl_parameters_to_opengl_log_file() {
    GLenum params[] = {
      GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS,
      GL_MAX_CUBE_MAP_TEXTURE_SIZE,
      GL_MAX_DRAW_BUFFERS,
      GL_MAX_FRAGMENT_UNIFORM_COMPONENTS,
      GL_MAX_TEXTURE_IMAGE_UNITS,
      GL_MAX_TEXTURE_SIZE,
      GL_MAX_VARYING_FLOATS,
      GL_MAX_VERTEX_ATTRIBS,
      GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS,
      GL_MAX_VERTEX_UNIFORM_COMPONENTS,
      GL_MAX_VIEWPORT_DIMS,
      GL_STEREO,
    };
    const char* names[] = {
      "GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS",
      "GL_MAX_CUBE_MAP_TEXTURE_SIZE",
      "GL_MAX_DRAW_BUFFERS",
      "GL_MAX_FRAGMENT_UNIFORM_COMPONENTS",
      "GL_MAX_TEXTURE_IMAGE_UNITS",
      "GL_MAX_TEXTURE_SIZE",
      "GL_MAX_VARYING_FLOATS",
      "GL_MAX_VERTEX_ATTRIBS",
      "GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS",
      "GL_MAX_VERTEX_UNIFORM_COMPONENTS",
      "GL_MAX_VIEWPORT_DIMS",
      "GL_STEREO",
    };
    write_to_opengl_log("OpenGL Context Parameters:\n");
    
    for (int i = 0; i < 10; i++) {
        int val = 0;
        glGetIntegerv(params[i], &val);
        write_to_opengl_log("%s %i\n", names[i], val);
    }
    
    int valarr[2];
    valarr[0] = valarr[1] = 0;
    glGetIntegerv(params[10], valarr);
    write_to_opengl_log("%s %i %i\n", names[10], valarr[0], valarr[1]);

    unsigned char val = 0;
    glGetBooleanv(params[11], &val);
    write_to_opengl_log("%s %u\n", names[11], (unsigned int)val);
}

void glfw_error_callback(int error, const char* description) {
    write_error_to_opengl_log_file("GLFW ERROR: code %i msg: %s\n", error, description);
}

int main(void)
{
    assert(start_opengl_log_file());
    write_to_opengl_log("GLFW version: %s\n\n", glfwGetVersionString());
    glfwSetErrorCallback(glfw_error_callback);
    if (!glfwInit()) {
        fprintf(stderr, "glfwInit() Error\n");
        return 1;
    }

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 6);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_SAMPLES, 4);
    
    GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "window title", NULL, NULL);
    if (!window) {
        printf("glfwCreateWindow() Error");
        glfwTerminate();
        return 1;
    }

    glfwMakeContextCurrent(window);

    glewExperimental = GL_TRUE;

    if (glewInit() != GLEW_OK) {
        printf("glewInit() Error");
        glfwDestroyWindow(window);
        glfwTerminate();
    }

    write_opengl_parameters_to_opengl_log_file();

    while (!glfwWindowShouldClose(window)) {
        glfwPollEvents();

        if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) {
            glfwSetWindowShouldClose(window, 1);
        }
    }

    glfwDestroyWindow(window);
    glfwTerminate();

    return 0;
}




/*
run:

time: Mon Mar 21 18:27:14 2022

GLFW version: 3.3.6 Win32 WGL EGL OSMesa VisualC

OpenGL Context Parameters:
GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS 192
GL_MAX_CUBE_MAP_TEXTURE_SIZE 32768
GL_MAX_DRAW_BUFFERS 8
GL_MAX_FRAGMENT_UNIFORM_COMPONENTS 4096
GL_MAX_TEXTURE_IMAGE_UNITS 32
GL_MAX_TEXTURE_SIZE 32768
GL_MAX_VARYING_FLOATS 0
GL_MAX_VERTEX_ATTRIBS 16
GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS 32
GL_MAX_VERTEX_UNIFORM_COMPONENTS 4096
GL_MAX_VIEWPORT_DIMS 32768 32768
GL_STEREO 0

*/

 

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