Opengl draw sine wave on a quad, getting black screen

I am trying to create a testing setup for my shaders using only OpenGL, GLUT, and glfw3. I started by editing tutorial 2 – red triangle from opengl-tutorial.org in order to render a black quad so that I could draw a fragment shader onto the screen. I read a post somewhere that said that was the best way to go about it but it didn’t provide any code examples. I wrote a very simple fragment shader to test that it works but I get the same black quad.

I have tried messing with glEnable to no avail. I have tried messing with my shader, only to change the color from black to white. I have tried looking at the other tutorials but they do not seem relevant to what I am trying to do.

Here is my shader code. I pasted it into this editor without the #version directive and it works fine.

#version 330 core
#ifdef GL_ES
precision mediump float;
#endif
uniform vec2 u_resolution;
float line(vec2 uv,float x,float width){
    return smoothstep(x-width,x,uv.y)-smoothstep(x,x+width,uv.y);
}
void main()
{
    vec2 uv=gl_FragCoord.xy/u_resolution;
    vec3 color=vec3(line(uv,sin(uv.x),.1));
    gl_FragColor=vec4(color,1.0);
}

Here is their main function with the quad taking up the whole screen instead of a triangle. It uses a function defined in shader.hpp called LoadShaders. I will paste the whole shader.cpp code at the bottom of this post.

#include <stdio.h>
#include <stdlib.h>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
GLFWwindow* window;
#include <glm/glm.hpp>
using namespace glm;
#include "common/shader.hpp"

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

    glfwWindowHint(GLFW_SAMPLES, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    // Open a window and create its OpenGL context
    window = glfwCreateWindow( 1024, 768, "Tutorial 02 - Red triangle", NULL, NULL);
    if( window == NULL ){
        fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
        getchar();
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

    // Initialize GLEW
    glewExperimental = true; // Needed for core profile
    if (glewInit() != GLEW_OK) {
        fprintf(stderr, "Failed to initialize GLEW\n");
        getchar();
        glfwTerminate();
        return -1;
    }

    // Ensure we can capture the escape key being pressed below
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
    
    // Dark blue background
    glClearColor(0.0f, 0.0f, 0.4f, 0.0f);
    
    GLuint VertexArrayID;
    glGenVertexArrays(1, &VertexArrayID);
    glBindVertexArray(VertexArrayID);

    // Create and compile our GLSL program from the shaders
    GLuint programID = LoadShaders( "SimpleVertexShader.vertexshader", "SimpleFragmentShader.fragmentshader" );


    static const GLfloat g_vertex_buffer_data[] = { 
        -1.0f, -1.0f, 0.0f,
         1.0f, -1.0f, 0.0f,
        -1.0f,  1.0f, 0.0f,
         1.0f,  1.0f, 0.0f,
         1.0f, -1.0f, 0.0f,

    };

    GLuint vertexbuffer;
    glGenBuffers(1, &vertexbuffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);
    glUniform2f(glGetUniformLocation(programID,"u_resolution"),1024, 768);
    do{

        // Clear the screen
        glClear( GL_COLOR_BUFFER_BIT );

        // Use our shader
        glUseProgram(programID);

        // 1rst attribute buffer : vertices
        glEnableVertexAttribArray(0);
        glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
        glVertexAttribPointer(
            0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
            3,                  // size
            GL_FLOAT,           // type
            GL_FALSE,           // normalized?
            0,                  // stride
            (void*)0            // array buffer offset
        );

        // Draw the triangle !
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 5); // 3 indices starting at 0 -> 1 triangle

        glDisableVertexAttribArray(0);

        // Swap buffers
        glfwSwapBuffers(window);
        glfwPollEvents();

    } // Check if the ESC key was pressed or the window was closed
    while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
           glfwWindowShouldClose(window) == 0 );

    // Cleanup VBO
    // glDeleteBuffers(1, &vertexbuffer);
    glDeleteVertexArrays(1, &VertexArrayID);
    glDeleteProgram(programID);

    // Close OpenGL window and terminate GLFW
    glfwTerminate();

    return 0;
}

the shader.cpp file. It does not output any error message when loading my shader

#include <stdio.h>
#include <string>
#include <vector>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <sstream>
using namespace std;

#include <stdlib.h>
#include <string.h>

#include <GL/glew.h>

#include "shader.hpp"

GLuint LoadShaders(const char * vertex_file_path,const char * fragment_file_path){

    // Create the shaders
    GLuint VertexShaderID = glCreateShader(GL_VERTEX_SHADER);
    GLuint FragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);

    // Read the Vertex Shader code from the file
    std::string VertexShaderCode;
    std::ifstream VertexShaderStream(vertex_file_path, std::ios::in);
    if(VertexShaderStream.is_open()){
        std::stringstream sstr;
        sstr << VertexShaderStream.rdbuf();
        VertexShaderCode = sstr.str();
        VertexShaderStream.close();
    }else{
        printf("Impossible to open %s. Are you in the right directory ? Don't forget to read the FAQ !\n", vertex_file_path);
        getchar();
        return 0;
    }

    // Read the Fragment Shader code from the file
    std::string FragmentShaderCode;
    std::ifstream FragmentShaderStream(fragment_file_path, std::ios::in);
    if(FragmentShaderStream.is_open()){
        std::stringstream sstr;
        sstr << FragmentShaderStream.rdbuf();
        FragmentShaderCode = sstr.str();
        FragmentShaderStream.close();
    }

    GLint Result = GL_FALSE;
    int InfoLogLength;


    // Compile Vertex Shader
    printf("Compiling shader : %s\n", vertex_file_path);
    char const * VertexSourcePointer = VertexShaderCode.c_str();
    glShaderSource(VertexShaderID, 1, &VertexSourcePointer , NULL);
    glCompileShader(VertexShaderID);

    // Check Vertex Shader
    glGetShaderiv(VertexShaderID, GL_COMPILE_STATUS, &Result);
    glGetShaderiv(VertexShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
    if ( InfoLogLength > 0 ){
        std::vector<char> VertexShaderErrorMessage(InfoLogLength+1);
        glGetShaderInfoLog(VertexShaderID, InfoLogLength, NULL, &VertexShaderErrorMessage[0]);
        printf("%s\n", &VertexShaderErrorMessage[0]);
    }



    // Compile Fragment Shader
    printf("Compiling shader : %s\n", fragment_file_path);
    char const * FragmentSourcePointer = FragmentShaderCode.c_str();
    glShaderSource(FragmentShaderID, 1, &FragmentSourcePointer , NULL);
    glCompileShader(FragmentShaderID);

    // Check Fragment Shader
    glGetShaderiv(FragmentShaderID, GL_COMPILE_STATUS, &Result);
    glGetShaderiv(FragmentShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
    if ( InfoLogLength > 0 ){
        std::vector<char> FragmentShaderErrorMessage(InfoLogLength+1);
        glGetShaderInfoLog(FragmentShaderID, InfoLogLength, NULL, &FragmentShaderErrorMessage[0]);
        printf("%s\n", &FragmentShaderErrorMessage[0]);
    }



    // Link the program
    printf("Linking program\n");
    GLuint ProgramID = glCreateProgram();
    glAttachShader(ProgramID, VertexShaderID);
    glAttachShader(ProgramID, FragmentShaderID);
    glLinkProgram(ProgramID);

    // Check the program
    glGetProgramiv(ProgramID, GL_LINK_STATUS, &Result);
    glGetProgramiv(ProgramID, GL_INFO_LOG_LENGTH, &InfoLogLength);
    if ( InfoLogLength > 0 ){
        std::vector<char> ProgramErrorMessage(InfoLogLength+1);
        glGetProgramInfoLog(ProgramID, InfoLogLength, NULL, &ProgramErrorMessage[0]);
        printf("%s\n", &ProgramErrorMessage[0]);
    }

    
    glDetachShader(ProgramID, VertexShaderID);
    glDetachShader(ProgramID, FragmentShaderID);
    
    glDeleteShader(VertexShaderID);
    glDeleteShader(FragmentShaderID);

    return ProgramID;
}

>Solution :

Actually, you should get an INVALID_OPERATION error (glGetError) because you call glUniform without having a program object installed. glUniform* specifies the value of a uniform variable for the current program object. So the program must be installed with glUseProgram before you can set the uniform:

GLint location = glGetUniformLocation(programID,"u_resolution");

glUseProgram(programID);
glUniform2f(location, 1024, 768);

Note that since OpenGL 4.1 you can alternatively use glProgramUniform (however not for OpenGL 3.3)