OpenGL triangle isn't rendering - c++

Question

I was following an OpenGL tutorial when I ran into an issue where I wasn't getting the expected outcome. I was expecting to see a triangle in a window, but instead, I got an empty window. I have made many changes to the code to help it run on my machine, but none fixed the issue. Some of these changes include adding:
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
to request the core profile context, adding a VAO with the VBO, I even downloaded the code from the tutorial, but to no avail. Does anyone know a way to fix my issue?
Code:
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
static unsigned int CompileShader(unsigned int type, const std::string& source){
unsigned int id = glCreateShader(type);
const char* src = source.c_str();
glShaderSource(id, 1, &src, nullptr);
glCompileShader(id);
int result;
glGetShaderiv(id, GL_COMPILE_STATUS, &result);
if(result == GL_FALSE){
int length;
glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
char* message = (char*)alloca(length * sizeof(char));
glGetShaderInfoLog(id, length, &length, message);
std::cout << "Failed to compile " << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader!" << std::endl;
std::cout << message << std::endl;
glDeleteShader(id);
return 0;
}
return id;
}
static unsigned int CreateShader(const std::string& vertexshader, const std::string& fragmentshader){
unsigned int program = glCreateProgram();
unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexshader);
unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentshader);
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
glValidateProgram(program);
glDeleteShader(vs);
glDeleteShader(fs);
return program;
}
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
if(glewInit() != GLEW_OK){
std::cout << "REEEEEEEEEEE" << std::endl;
}
float vertices[6] = {
-0.5f, -0.5f,
0.0f, 0.5f,
-0.5f, -0.5f
};
unsigned int buf;
glGenBuffers(1, &buf);
glBindBuffer(GL_ARRAY_BUFFER, buf);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), vertices, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
std::string vertexshader =
"#version 330 core\n"
"\n"
"in vec4 position;\n"
"out vec4 color;\n"
"\n"
"void main(){\n"
" gl_Position = position;\n"
" color = position;\n"
"}\n";
std::string fragmentshader =
"#version 330 core\n"
"\n"
"in vec4 in_color;\n"
"out vec4 color;\n"
"\n"
"void main(){\n"
" color = in_color;\n"
"}\n";
unsigned int shader = CreateShader(vertexshader, fragmentshader);
glUseProgram(shader);
glClearColor(0.33f, 0.33f, 0.33f, 1.0f);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwTerminate();
return 0;
}
CMakeLists:
cmake_minimum_required (VERSION 3.5)
if(POLICY CMP0072)
cmake_policy(SET CMP0072 NEW)
else(NOT POLICY CMP0072)
message(STATUS "Error")
endif(POLICY CMP0072)
project (opengl-learning)
find_package(PkgConfig REQUIRED)
pkg_search_module(GLFW REQUIRED glfw3)
include_directories(${GLFW_INCLUDE_DIRS} ${OPENGL_INCLUDE_DIR})
set (GCC_COVERAGE_LINK_FLAGS "-lglfw3 -pthread -ldl -lGLU -lGL -lrt -lXrandr -lXxf86vm -lXi -lXinerama -lX11 -lGLEW -lGLU -lGL")
add_definitions(${GCC_COVERAGE_COMPILE_FLAGS})
set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -std=c++14")
set (source_dir "${PROJECT_SOURCE_DIR}/src/")
file (GLOB source_files "${source_dir}/*.cpp")
add_executable (opengl-learning ${source_files})
find_package(OpenGL REQUIRED)
find_package(GLEW REQUIRED)
target_link_libraries(opengl-learning ${GLFW_LIBRARIES} ${GLEW_LIBRARIES} ${OPENGL_LIBRARIES})
Versions (requesting core profile)
glGetString(GL_VERSION) >> 3.3 (Core Profile) Mesa 18.3.6
glGetString(GL_SHADING_LANGUAGE_VERSION) >> 3.30
OS: Linux Debian 10
If any extra information is required, feel free to ask.

Answer 1

When you use a core profile OpenGL Context you must create a Vertex Array Object:
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glBindBuffer(GL_ARRAY_BUFFER, buf);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
The default Vertex Array Object (0) is only valid using a compatibility profile OpenGL context:
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);
I recommend reading Vertex Specification.