OpenGL primitive Restart

Im learning about opengl 4.3 and I am doing an 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?

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 {
private:
    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;*/
public:

    Demo_OGL_2();
    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:
            switch(event->key.keysym.sym){
                case SDLK_v:
                    std::cout << glGetString(GL_VERSION) << std::endl;
                    break;
                case SDLK_ESCAPE:
                    running = false;
                    break;
                default:
                    break;
            }
            break;
        case SDL_QUIT:
            running = false;
            break;
        default:
            break;
    }
}
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);

    glEnable(GL_CULL_FACE);
    glDisable(GL_DEPTH_TEST);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glUseProgram(render_prog);

    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]);


#define USE_PRIMITIVE_RESTART 0
#if USE_PRIMITIVE_RESTART
    // When primitive restart is on, we can call one draw command
    glEnable(GL_PRIMITIVE_RESTART);
    glPrimitiveRestartIndex(0xFFFF);
    glDrawElements(GL_TRIANGLE_STRIP, 17, GL_UNSIGNED_SHORT, NULL);
#else
    // Without primitive restart, we need to call two draw commands
    glDrawElements(GL_TRIANGLE_STRIP, 8, GL_UNSIGNED_SHORT, NULL);
    glDrawElements(GL_TRIANGLE_STRIP, 8, GL_UNSIGNED_SHORT,
    (const GLvoid *)(9 * sizeof(GLushort)));
#endif


    SDL_GL_SwapWindow(window);
}

void Demo_OGL_2::OnCleanup() {
    glUseProgram(0);
    glDeleteProgram(render_prog);
    glDeleteVertexArrays(1, vao);
    glDeleteBuffers(1, vbo);
    SDL_GL_DeleteContext(ctxt);
    SDL_DestroyWindow(window);
    SDL_Quit();
}

bool Demo_OGL_2::OnInit() {
    if(SDL_Init(SDL_INIT_EVERYTHING) < 0)
        return false;

    window = SDL_CreateWindow(WIN_TITLE,
            SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
            WIN_WIDTH, WIN_HEIGHT,
            SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL);
    if(!window)
        return false;

    setupOpenGl();
    exInit();

    running = true;

    return true;
}
void Demo_OGL_2::setupOpenGl(){
   //SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
   //SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
   SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
   SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 32);
   ctxt = SDL_GL_CreateContext(window);

   //vsync ON
   SDL_GL_SetSwapInterval(1);

   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);
    glBindVertexArray(vao[0]);

    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));
    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);

    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))
            Event(&event);

        Loop();
        Render();
    }

    Cleanup();

    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;
}


vmath::mat4 model_matrix(vmath::translate(0.0f, 0.0f, -5.0f) *
vmath::rotate(t * 360.0f, Y) *
vmath::rotate(t * 720.0f, Z));

These rotation do nothing but I would keep my roations in the range 0 <= r < 360.

You have placed your camera at 0,0,-5 looking down the -z axis
You have placed your object at 0,0,0

So you are not looking at your object

vmath::mat4 model_matrix(vmath::translate(0.0f, 0.0f, 5.0f)

In general it is easier to use a lookat function to place cameras

“t” is between 0-1, rotate use a fraction of 360 and 720, i think that this rotations are alright.

model_matrix is a transformation matrix for cube, not for camera, then, camera is on 0,0,0 looking at -Z and cube on 0,0,-5. thats alright? i was testing with 0,0,5 , 0,5,0 , 0,-5,0 … And still black window. I dont know what should i do. Any suggestion?

Try changing your projection matrix. Perhaps 1,-1, and aspect are too narrow. Or you could try the alternate way of setting the projection matrix with angle and aspect

Those are normalized values if im on the right way. Anyway, i tryed bigger values and still the same result.
Im sure, that im forgetting something. Someone can compile and test it?

glUniformMatrix4fv(render_model_matrix_loc, 4, GL_FALSE, model_matrix);

Replace 4 with 1. model_matrix is a single matrix and not an array of 4 matrices. I suppose you’re getting an INVALID_OPERATION here, thus no model is uploaded and thus no transformation is happening.

Oh thx, it is working now!!! i can continue with my learning :slight_smile:
manythx again!

You’re welcome.

Oh thx, it is working now!!! i can continue with my learning :slight_smile:

A sound advice: In case of emergency, always check for GL errors first! :slight_smile:

Thx, i will!