Transform feedback tutorial, not getting the desired output?

Not sure if this is the problem, but I’ll post my opengl version on linux anyways.

 glxinfo | grep 'version'
server glx version string: 1.4
client glx version string: 1.4
GLX version: 1.4
    Max core profile version: 3.3
    Max compat profile version: 3.0
    Max GLES1 profile version: 1.1
    Max GLES[23] profile version: 3.0
OpenGL core profile version string: 3.3 (Core Profile) Mesa 17.2.4
OpenGL core profile shading language version string: 3.30
OpenGL version string: 3.0 Mesa 17.2.4
OpenGL shading language version string: 1.30
OpenGL ES profile version string: OpenGL ES 3.0 Mesa 17.2.4
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.00

Anyways I’m following the tutorial on this page and my output is a string of zero’s instead of the
normal square roots of 1 to 5. Here’s the code; it compiles with these libs in codeblocks


Here’s the code

// Link statically with GLEW

// Headers
#include <GL/glew.h>
#include <SFML/Window.hpp>

// Vertex shader
const GLchar* vertexShaderSrc = R"glsl(        in float inValue;    out float geoValue;    void main()    {        geoValue = sqrt(inValue);    } )glsl";

// Geometry shader
const GLchar* geoShaderSrc = R"glsl(        layout(points) in;    layout(triangle_strip, max_vertices = 3) out;    in float[] geoValue;    out float outValue;    void main()    {        for (int i = 0; i < 3; i++)        {            outValue = geoValue[0] + i;            EmitVertex();        }        EndPrimitive();    } )glsl";

int main()
    sf::ContextSettings settings;
    settings.depthBits = 24;
    settings.stencilBits = 8;

    sf::Window window(sf::VideoMode(800, 600, 32), "Transform Feedback", sf::Style::Titlebar | sf::Style::Close, settings);

    // Initialize GLEW
    glewExperimental = GL_TRUE;

    // Compile shaders
    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSrc, nullptr);

    GLuint geoShader = glCreateShader(GL_GEOMETRY_SHADER);
    glShaderSource(geoShader, 1, &geoShaderSrc, nullptr);

    // Create program and specify transform feedback variables
    GLuint program = glCreateProgram();
    glAttachShader(program, vertexShader);
    glAttachShader(program, geoShader);

    const GLchar* feedbackVaryings[] = { "outValue" };
    glTransformFeedbackVaryings(program, 1, feedbackVaryings, GL_INTERLEAVED_ATTRIBS);


    // Create VAO
    GLuint vao;
    glGenVertexArrays(1, &vao);

    // Create input VBO and vertex format
    GLfloat data[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f };

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(data), data, GL_STATIC_DRAW);

    GLint inputAttrib = glGetAttribLocation(program, "inValue");
    glVertexAttribPointer(inputAttrib, 1, GL_FLOAT, GL_FALSE, 0, 0);

    // Create transform feedback buffer
    GLuint tbo;
    glGenBuffers(1, &tbo);
    glBindBuffer(GL_ARRAY_BUFFER, tbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(data) * 3, nullptr, GL_STATIC_READ);

    // Perform feedback transform

    glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, tbo);

        glDrawArrays(GL_POINTS, 0, 5);



    // Fetch and print results
    GLfloat feedback[15];
    glGetBufferSubData(GL_TRANSFORM_FEEDBACK_BUFFER, 0, sizeof(feedback), feedback);

    for (int i = 0; i < 15; i++)
", feedback[i]);


    glDeleteBuffers(1, &tbo);
    glDeleteBuffers(1, &vbo);

    glDeleteVertexArrays(1, &vao);


    return 0;

I removed the version numbers from the shaders as neither 150 or 130 work. thanks ahead!

Check shader compilation status with glGetShaderiv(GL_COMPILE_STATUS), linking status with glGetProgramiv(GL_LINK_STATUS), and general error status with glGetError().

The default GLSL version is 1.10. To compile your shaders, I think you’ll find you’ll need something greater like:

#version 150

[QUOTE=Dark Photon;1290544]The default GLSL version is 1.10. To compile your shaders, I think you’ll find you’ll need something greater like:

#version 150


Mines at 130 so I would need a newer gpu, correct?

If your GPU doesn’t support OpenGL 3.2 (GLSL 1.50), then yes as that version added Geometry Shader support via GLSL.