OpenGL shaders not working with uniform variable

Question

I'm trying to write a code to draw a triangle with changing color, following the tutorial LearnOpenGL - Shaders.

But my code doesn't work, the triangle is blinking instead of gradually change the color, I don't know if it is a hardware or software problem.

Can anyone help me?

I'm using OpenGL 3.0 with Mesa 18.3.4.

And compiling with gcc shaders_change.c -lGL -lglfw -lm

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <GL/gl.h>
#include <GLFW/glfw3.h>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

const char *vertexShaderSource ="#version 330 core\n"
  "layout (location = 0) in vec3 aPos;\n"
  "void main()\n"
  "{\n"
  "   gl_Position = vec4(aPos, 1.0);\n"
  "}\n\0";

const char *fragmentShaderSource = "#version 330\n"
  "out vec4 FragColor;\n"
  "uniform vec4 ourColor;\n"
  "void main()\n"
  "{\n"
  "   FragColor = ourColor;\n"
  "}\n\0";

int main(){
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
      printf("Failed to create GLFW window");
      glfwTerminate();
      return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // build and compile our shader program
    // ------------------------------------
    // vertex shader
    int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        printf("ERROR::SHADER::VERTEX::COMPILATION_FAILED\n%s",infoLog);
    }
    // fragment shader
    int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
    printf("ERROR::SHADER::VERTEX::COMPILATION_FAILED\n%s",infoLog);
    }
    // link shaders
    int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    // check for linking errors
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
      glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
      printf("ERROR::SHADER::VERTEX::COMPILATION_FAILED\n%s",infoLog);
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        // positions         // colors
         0.5f, -0.5f, 0.0f,  // bottom right
        -0.5f, -0.5f, 0.0f,  // bottom left
         0.0f,  0.5f, 0.0f,  // top 
    };

    unsigned int VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    // bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), 0);
    glEnableVertexAttribArray(0);
    // color attribute
    //glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(3 * sizeof(float)));
    //glEnableVertexAttribArray(VAO);

    // You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
    // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.

    // as we only have a single shader, we could also just activate our shader once beforehand if we want to
    glBindVertexArray(VAO);

    // render loop
    // -----------
    float timeValue;
    float greenValue;
    int vertexColorLocation;
    while (!glfwWindowShouldClose(window)){
        // input
        // -----
        processInput(window);

    // render
        // ------
        //glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

    glUseProgram(shaderProgram);

    timeValue = glfwGetTime();
    greenValue = sin(timeValue) / 2.0f + 0.5f;
    vertexColorLocation = glGetUniformLocation(shaderProgram, "ourColor");
    glUniform4f(vertexColorLocation, 0.0f, greenValue, 0.0f, 1.0f);

        // render the triangle
    glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

void processInput(GLFWwindow *window){
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, 1);
}

void framebuffer_size_callback(GLFWwindow* window, int width, int height){
    glViewport(0, 0, width, height);
}

Answer 1

thank you all for help!! I'd discover what is my problem, I'd just forgot to include de glad.h library and the libdl.