Debugging

gltest.c

// clang gltest.c -lglfw -lglew -framework OpenGL -o gltest

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

void glAssertNoError(const char *msg) {
    int code = glGetError();
    if (code == GL_NO_ERROR) {
        return;
    }
    fprintf(stderr, "OpenGL error: %d, %s\n", code, msg);
}

int main() {
    // Initialize GLFW first
    if (!glfwInit()) {
        fprintf(stderr, "Failed to initialize GLFW\n");
        return -1;
    }

    // Then setup hints for OpenGL 4.1
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    // Now we can create the window
    GLFWwindow* window = glfwCreateWindow(800, 600, "OpenGL Program", NULL, NULL);
    if (!window) {
        fprintf(stderr, "Failed to create GLFW window\n");

        const char* description;
        int code = glfwGetError(&description);
        fprintf(stderr, "Error %d: %s\n", code, description);

        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    // and initialize GLEW
    if (glewInit() != GLEW_OK) {
        fprintf(stderr, "Failed to initialize GLEW\n");
        glfwTerminate();
        return -1;
    }

    fprintf(stderr, "OpenGL version: %s\n", glGetString(GL_VERSION));
    fprintf(stderr, "GLSL version: %s\n", glGetString(GL_SHADING_LANGUAGE_VERSION));

    while (!glfwWindowShouldClose(window)) {

        // white background
        glClearColor(1.0, 1.0, 1.0, 1.0);
        glAssertNoError("glClearColor");
        glClear(GL_COLOR_BUFFER_BIT);
        glAssertNoError("glClear");

        // red triangle
        glBegin(GL_TRIANGLES);
        glAssertNoError("glBegin");
        glColor3f(1.0, 0.0, 0.0);
        glAssertNoError("glColor3f");
        glVertex2f(-0.5, -0.5);
        glAssertNoError("glVertex2f");
        glVertex2f(0.5, -0.5);
        glAssertNoError("glVertex2f");
        glVertex2f(0.0, 0.5);
        glAssertNoError("glVertex2f");
        glEnd();
        glAssertNoError("glEnd");

        glfwSwapBuffers(window);
        glAssertNoError("glfwSwapBuffers");

        glfwPollEvents();
        glAssertNoError("glfwPollEvents");
    }

    glfwTerminate();
    return 0;
}