GLFW and GLEW not showing triangle red - c++

Question

My code does not display a red triangle, instead there is a black screen. I was following the OpenGL tutorial by The Cherno. This happened at end of the 7th episode. I am using Visual Studio 2019 with Visual C++ on Windows 10 Home. My Graphics Card is a NVidia 820m.Link for tutorial I was following.
#include <gl/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <fstream>
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 legnth;
glGetShaderiv(id, GL_INFO_LOG_LENGTH, &legnth);
char* message = (char*)alloca(legnth * sizeof(char));
glGetShaderInfoLog(id, legnth, &legnth, message);
std::cout << "Failed to Compile" << (type == GL_VERTEX_SHADER ? "Vertex: Shader:\n" : "Fragment Shader:\n");
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;
if (!glewInit())
return -1;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Cooked Pixel", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK)
{
std::cout << "Error: GLEW is not initialized \n";
}
std::cout << "GL Version" << glGetString(GL_VERSION) << "\n";
float positions[6] = {
-0.5, -0.5,
0.0, -0.5,
0.5, -0.5
};
unsigned int buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), positions, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
std::string vertexShader = R"glsl(
#version 330 core
layout(location = 0) in vec4 position;
void main()
{
gl_Position = position;
}
)glsl";
std::string fragmentShader = R"glsl(
#version 330 core
layout(location = 0) out vec4 color;
void main()
{
color = vec4(1.0, 0.0, 0.0, 1.0);
}
)glsl";
unsigned int shader = CreateShader(vertexShader, fragmentShader);
glUseProgram(shader);
glfwMaximizeWindow(window);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
/* Very Old Code
glBegin(GL_TRIANGLES);
glVertex2f(-1.0, -1.0);
glVertex2f(0, -1.0);
glVertex2f(0, -3.0);
glEnd();
*/
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwTerminate();
return 0;
}

Answer 1

Your "triangle" is not a triangle, it is just a straight line.
float positions[6] = {
-0.5, -0.5,
0.0, -0.5,
0.5, -0.5
};
Change the vertex coordinates:
float positions[6] = {
-0.5, -0.5,
0.0, -0.5,
0.5, 0.5
};
Do not call glewInit() twice. Call it just once after making the OpenGL Context current with glfwMakeContextCurrent.
Additinaly you should create a Vertex Array Object:
unsigned int vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
unsigned int buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), positions, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);