CODEWITHSUNDEEP
glfwopengl-3
anekix
anekix

Reputation: 2563

simple opengl triangle program with glfw renders black screen

i have a simple program that creates a triangle on the screen using OpenGL & glfw here is the code.on running this with g++ -std=c++11 main.cpp src/glad.c -o out -Iinclude -lGL -lGLU -lglfw3 -lX11 -lXxf86vm -lXrandr -lpthread -lXi -ldl i get a window which opens up & then gets closed with core dumped message on screen. what could be wrong? .

NOTE: i managed to remove that error but now i have a black empty screen . here is my new code.what could be the reason for this

#include <glad/glad.h>
#include <GLFW/glfw3.h>

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);
    gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);

    // An array of 3 vectors which represents 3 vertices
    static const GLfloat g_vertex_buffer_data[] = {
       -1.0f, -1.0f, 0.0f,
       1.0f, -1.0f, 0.0f,
       0.0f,  1.0f, 0.0f,
    };


    // This will identify our vertex buffer
    GLuint vertexbuffer;
    // Generate 1 buffer, put the resulting identifier in vertexbuffer
    glGenBuffers(1, &vertexbuffer);
    // The following commands will talk about our 'vertexbuffer' buffer
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    // Give our vertices to OpenGL.
    glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);



    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {

    // 1st 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_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle
        glDisableVertexAttribArray(0);

        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

Upvotes: 1

Views: 735

Answers (1)

Rabbid76
Rabbid76

Reputation: 210878

First you render the scene:

glDrawArrays(GL_TRIANGLES, 0, 3);

But then the framebuffer and so the rendering is cleared immediately:

glClear(GL_COLOR_BUFFER_BIT);

Clear the color plane of the default framebuffer, before you do any rendering:

while (!glfwWindowShouldClose(window))
{
    glClear(GL_COLOR_BUFFER_BIT);

    ....

Since GLFW uses double buffering, it would also work, if you clear the default framebuffer immediately after swapping the buffers: 

glfwSwapBuffers(window);
glClear(GL_COLOR_BUFFER_BIT);

Upvotes: 1

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