How to fix black screen output in OpenGL 3.3 - c++

Question

I am experiencing a black screen in my project using OpenGL and C++. I am in need of assistance as to where I went wrong rendering a red triangle to the screen.
I have tried checking for errors in the vertex and fragment shader.
#include <GL\glew.h>
#include <GL\GL.h>
#include <GLFW\glfw3.h>
#include <iostream>
#include <string>
using namespace std;
unsigned int CreateShader(int type, const string shaderSource) {
unsigned int shader = glCreateShader(type);
const char *src = shaderSource.c_str();
glShaderSource(shader, 1, &src, NULL);
glCompileShader(shader);
int result;
glGetShaderiv(shader, GL_COMPILE_STATUS, &result);
if (result == GL_FALSE) {
int length;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &length);
char *message = (char*)alloca(length * sizeof(char));
glGetShaderInfoLog(shader, length, &length, message);
cout << "Failed to compile " << (type == GL_VERTEX_SHADER ? "vertex shader " : "fragment shader ") << endl;
cout << message << endl;
}
return shader;
}
unsigned int CreateProgram(const string vertexShader, const string fragmentShader) {
unsigned int program = glCreateProgram();
unsigned int vs = CreateShader(GL_VERTEX_SHADER, vertexShader);
unsigned int fs = CreateShader(GL_FRAGMENT_SHADER, fragmentShader);
glAttachShader(program, vs);
glAttachShader(program, fs);
glDeleteShader(vs);
glDeleteShader(fs);
glLinkProgram(program);
glValidateProgram(program);
return program;
}
int main() {
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
GLFWwindow *window = glfwCreateWindow(800, 600, "window", NULL, NULL);
glfwMakeContextCurrent(window);
glewInit();
if (glewInit() != GLEW_OK) {
cout << "Glew initialization Failed! " << endl;
glfwTerminate();
return -1;
}
float positions[] = {
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
0.0f, 0.5f, 0.0f,
};
cout << "Made By Rial Seebran" << endl;
cout << glfwGetVersionString() << endl;
unsigned int VAO;
unsigned int VBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
const string vertexShader =
"#version 330 core\n"
"layout (location = 0) in vec3 position;\n"
"void main() {\n"
"gl_Position = vec4(position, 0.0f);\n"
"}\n";
const string fragmentShader =
"#version 330 core\n"
"layout (location = 0) out vec4 color;\n"
"void main() {\n"
"color = vec4(1.0f, 0.0f, 0.0f, 1.0f);\n"
"}\n";
unsigned int program = CreateProgram(vertexShader, fragmentShader);
while (!glfwWindowShouldClose(window)) {
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(program);
glBindVertexArray(VAO);
glDrawArrays(GL_ARRAY_BUFFER, 0, 3);
glBindVertexArray(0);
glfwPollEvents();
glfwSwapBuffers(window);
}
glfwTerminate();
return 0;
}
I'm expecting a red triangle drawn at the coordinates specified with a blueish background.

Answer 1

The first parameter to glDrawArrays has to be the primitive type.
It has to be GL_TRIANGLES rather than GL_ARRAY_BUFFER:
glDrawArrays(GL_ARRAY_BUFFER, 0, 3);
glDrawArrays(GL_TRIANGLES, 0, 3);
The OpenGL enumerator constant GL_ARRAY_BUFFER is not an an accepted value for this parameter and will cause an GL_INVALID_ENUM error (The error can be get by glGetError).
When the clip space coordinate is transformed to normalized device space, then the x, y and z component is divided by the w component.
This means the w component of gl_Position has to be set 1.0 rather the 0.0:
gl_Position = vec4(position, 0.0f);
gl_Position = vec4(position, 1.0);
Glew can enable additional extensions by glewExperimental = GL_TRUE;. See the GLEW documentation which says:
GLEW obtains information on the supported extensions from the graphics driver. Experimental or pre-release drivers, however, might not report every available extension through the standard mechanism, in which case GLEW will report it unsupported. To circumvent this situation, the glewExperimental global switch can be turned on by setting it to GL_TRUE before calling glewInit(), which ensures that all extensions with valid entry points will be exposed.
glewExperimental = GL_TRUE;
if ( glewInit() != GLEW_OK ) {
cout << "Glew initialization Failed! " << endl;
glfwTerminate();
return -1;
}