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SDL 2 C++ OpenGL Problem

2 posts in this topic

Im a begginer in opengl and Im learning about opengl 4.3.

I am doing a reference guide book's example using SDL 2.0. 
The only thing that i can see is a black window, i dont know what i should do. Anyone can help me?

I tryied many things such as modifing frutum and translation. Any idea?

Here is my code:

This is Demo_OGL_2.h:

#ifndef DEMO_OGL_II_H_
#define DEMO_OGL_II_H_
#include <iostream>
#include <GL/gl3w.h>
#include <GL/gl3.h>
#include "SDL2/SDL.h"
#include "LoadShaders.h"
class Demo_OGL_2 {
    bool running;
    SDL_Window* window;
    SDL_GLContext ctxt;
    static const uint32_t   WIN_HEIGHT = 768; //px
    static const uint32_t   WIN_WIDTH  = 1024; //px
    static const char*      WIN_TITLE; //px
    float aspect;
    static const GLfloat cube_positions[];
    static const GLfloat cube_colors[];
    static const GLushort cube_indices[];
    GLuint ebo[1];
    GLuint vao[1];
    GLuint vbo[1];
    GLuint render_prog;
    GLuint render_model_matrix_loc;
    GLuint render_projection_matrix_loc;
    enum VAO_IDs { Triangles, NumVAOs };
    enum Buffer_IDs { ArrayBuffer, NumBuffers };
    enum Attrib_IDs { vPosition = 0, vColor = 1 };
    GLuint  VAOs[NumVAOs];
    GLuint  Buffers[NumBuffers];
    static const GLuint  NumVertices = 6;*/
    int Execute(){ return OnExecute(); }
    bool Init(){ return OnInit(); }
    void Loop(){ return OnLoop(); }
    void Render(){ return OnRender(); }
    void Cleanup(){ return OnCleanup(); }
    void Event(SDL_Event* Event){ OnEvent(Event); }
    int OnExecute();
    bool OnInit();
    void OnEvent(SDL_Event* Event);
    void OnLoop();
    void OnRender();
    void OnCleanup();
    void setupOpenGl();
    void exInit();
#endif /* DEMO_OGL_I_H_ */

And this is my Demo_OGL_2.cpp:

#include <iostream>
#include "Demo_OGL_2.h"
#include "../../LibsNUtils/vmath.h"
#include <GL/gl3w.h>
#include <GL/gl3.h>
#include "LoadShaders.h"
//#define BUFFER_OFFSET(offset) ((void *) (offset))
const char* Demo_OGL_2::WIN_TITLE = "Titulo de la Ventana";
const GLfloat Demo_OGL_2::cube_positions[] = {
        -1.0f, -1.0f, -1.0f, 1.0f,
        -1.0f, -1.0f,  1.0f, 1.0f,
        -1.0f,  1.0f, -1.0f, 1.0f,
        -1.0f,  1.0f,  1.0f, 1.0f,
         1.0f, -1.0f, -1.0f, 1.0f,
         1.0f, -1.0f,  1.0f, 1.0f,
         1.0f,  1.0f, -1.0f, 1.0f,
         1.0f,  1.0f,  1.0f, 1.0f
const GLfloat Demo_OGL_2::cube_colors[] = {
         1.0f,  1.0f,  1.0f,  1.0f,
         1.0f,  1.0f,  0.0f,  1.0f,
         1.0f,  0.0f,  1.0f,  1.0f,
         1.0f,  0.0f,  0.0f,  1.0f,
         0.0f,  1.0f,  1.0f,  1.0f,
         0.0f,  1.0f,  0.0f,  1.0f,
         0.0f,  0.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  1.0f
const GLushort Demo_OGL_2::cube_indices[] = {
        0, 1, 2, 3, 6, 7, 4, 5, // First strip
        0xFFFF, // <<-- This is the restart index
        2, 6, 0, 4, 1, 5, 3, 7 // Second strip
Demo_OGL_2::Demo_OGL_2() : running(false), window(NULL), ctxt(NULL),
            aspect(0), ebo(), vao(), vbo(),
            render_prog(0), render_model_matrix_loc(0), render_projection_matrix_loc(0){}
void Demo_OGL_2::OnEvent(SDL_Event* event) {
    switch (event->type) {
        case SDL_KEYUP:
                case SDLK_v:
                    std::cout << glGetString(GL_VERSION) << std::endl;
                case SDLK_ESCAPE:
                    running = false;
        case SDL_QUIT:
            running = false;
void Demo_OGL_2::OnLoop() {}
void Demo_OGL_2::OnRender() {
    float t = float(GetTickCount() & 0x1FFF) / float(0x1FFF);
    //static float q = 0.0f;
    static const vmath::vec3 X(1.0f, 0.0f, 0.0f);
    static const vmath::vec3 Y(0.0f, 1.0f, 0.0f);
    static const vmath::vec3 Z(0.0f, 0.0f, 1.0f);
    vmath::mat4 model_matrix(vmath::translate(0.0f, 0.0f, -5.0f) *
                                vmath::rotate(t * 360.0f, Y) *
                                vmath::rotate(t * 720.0f, Z));
    vmath::mat4 projection_matrix(vmath::frustum(-1.0f, 1.0f, -aspect, aspect, 1.0f, 500.0f));
    glUniformMatrix4fv(render_model_matrix_loc, 4, GL_FALSE, model_matrix);
    glUniformMatrix4fv(render_projection_matrix_loc, 1, GL_FALSE, projection_matrix);
    glBindVertexArray( vao[0] );
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo[0]);
    // When primitive restart is on, we can call one draw command
    // Without primitive restart, we need to call two draw commands
    (const GLvoid *)(9 * sizeof(GLushort)));
void Demo_OGL_2::OnCleanup() {
    glDeleteVertexArrays(1, vao);
    glDeleteBuffers(1, vbo);
bool Demo_OGL_2::OnInit() {
        return false;
    window = SDL_CreateWindow(WIN_TITLE,
            WIN_WIDTH, WIN_HEIGHT,
        return false;
    running = true;
    return true;
void Demo_OGL_2::setupOpenGl(){
   SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 32);
   ctxt = SDL_GL_CreateContext(window);
   //vsync ON
   if (gl3wInit()) {
       std::cout << "Error al Inicializar GL3W" << std::endl;
void Demo_OGL_2::exInit(){
    ShaderInfo shaders[] = {
         { GL_VERTEX_SHADER, "Resources/Demo_OGL_II/primitive_restart.vs.glsl" },
         { GL_FRAGMENT_SHADER, "Resources/Demo_OGL_II/primitive_restart.fs.glsl" },
         { GL_NONE, NULL }
    render_prog = LoadShaders( shaders );
    glUseProgram( render_prog );
    render_model_matrix_loc = glGetUniformLocation(render_prog, "model_matrix");
    render_projection_matrix_loc = glGetUniformLocation(render_prog, "projection_matrix");
    glGenBuffers(1, ebo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo[0]);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(cube_indices), cube_indices, GL_STATIC_DRAW);
    glGenVertexArrays(1, vao);
    glGenBuffers(1, vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(cube_positions) + sizeof(cube_colors), NULL, GL_STATIC_DRAW);
    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(cube_positions), cube_positions );
    glBufferSubData(GL_ARRAY_BUFFER, sizeof(cube_positions), sizeof(cube_colors), cube_colors);
    glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, NULL);
    glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (const GLvoid*)sizeof(cube_positions));
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glViewport(0, 0, WIN_WIDTH, WIN_HEIGHT);
    aspect = float(WIN_HEIGHT) / float(WIN_WIDTH);
int Demo_OGL_2::OnExecute() {
    if (!Init())
        return -1;
    SDL_Event event;
    while (running) {
        while (SDL_PollEvent(&event))
    return 0;

Vertex Shader:

#version 330
uniform mat4 model_matrix;
uniform mat4 projection_matrix;
layout (location = 0) in vec4 position;
layout (location = 1) in vec4 color;
out vec4 vs_fs_color;
void main(void)
    vs_fs_color = color;
    gl_Position = projection_matrix * (model_matrix * position);

And the simplest fragment shader:

#version 430
in vec4 vs_fs_color;
layout (location = 0) out vec4 color;
void main(void)
    color = vs_fs_color;

if u want to try it, just do:


 Demo_OGL_2 d;

 return d.Execute();

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That's a lot of moving parts. Have you managed to draw anything before, like with a previous tutorial? Anything at all?

First the low-hanging fruit: I'd check for GL errors at the end of the render loop, check that there were no errors compiling and linking the shaders, and I'd turn face culling off just in case.

Then I'd try to draw *something* on the screen, like a single triangle or a couple of points, as fast as possible. Strip out and simplify large chunks of code until you see something. Then you can start re-adding the stuff piece by piece and see which of them was the problem.

Assuming your GL is in compatibility mode, you can initially disable the shader program and just draw your primitive with glBegin, glVertex etc. If that works, try to draw with the simplest possible shaders, like a vertex shader that ignores input entirely and outputs the positions of a single fixed triangle based on gl_VertexID, and a fragment shader that outputs constant white. Then add the position input back in, add indexed drawing, etc.

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Yes, I tryed some tutorials before. I post in opengl forums too. They solved it!. 

I had to change only one line:


  1. glUniformMatrix4fv(render_model_matrix_loc, 4, GL_FALSE, model_matrix);
  2. to:

    glUniformMatrix4fv(render_model_matrix_loc, 1, GL_FALSE, model_matrix);

thx anyway!!


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