C++ Opengl triangles is drawing or not visible at all - c++

Question

My code is not showing the triangle at all i tried debugging it step by step but no luck. What's wrong in my 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 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;
/* 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 << "Error!" << std::endl;
float positions[6] = {-0.5f, -0.5f, 0.0f, 0.0f, 0.5f, 0.5f};
unsigned int buffer = 0;
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 =
"#version 330 core\n"
"\n"
"layout(location=0)in vec4 position;\n"
"\n"
"void main()\n"
"{\n"
" gl_Position = position;\n"
"}\n";
std::string fragmentShader =
"#version 330 core\n"
"\n"
"layout(location=0)out vec4 color;\n"
"\n"
"void main()\n"
"{\n"
" color = vec4(0.0, 0.0, 1.0, 1.0);\n"
"}\n";
unsigned int shader = CreateShader(vertexShader, fragmentShader);
glUseProgram(shader);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glBindVertexArray(buffer);
glDrawArrays(GL_TRIANGLES, 0, 3);
glfwPollEvents();
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glDeleteShader(shader);
glfwTerminate();
return 0;
}

Answer 1

Your "triangle" is not a triangle it is a line, so you can't see it:
float positions[6] = {-0.5f, -0.5f, 0.0f, 0.0f, 0.5f, 0.5f};
Change it to:
float positions[6] = {-0.5f, -0.5f, 0.5f, 0.0f, 0.0f, 0.5f};