opengl 3.3 core profile render fails

0
votes

I'm trying to render a simple test shader with the opengl 3.3 core profile. but everything I get is a black window.

GLFWwindow* window;

GLuint vao;
GLuint vbo[2];
GLuint program;

const GLfloat square[8] = {
    -1.0, -1.0,
    -1.0,  1.0,
    1.0,  1.0,
    1.0, -1.0
};

const GLfloat indices[4] = { 0, 1, 2, 3 };

init opengl core context and window

if( !glfwInit() ) {
    std::cerr << "Failed to initialize GLFW\n";
    return -1;
}

glfwWindowHint(GLFW_SAMPLES, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

// Open a window and create its OpenGL context
window = glfwCreateWindow( 1024, 768, "", 0, 0);
if( window == NULL ) {
    std::cerr << "Failed to open GLFW window.\n";
    glfwTerminate();
    return -1;
}
glfwMakeContextCurrent(window);

// Initialize GLEW
if (gl3wInit()) {
    std::cerr << "Failed to initialize GLEW" << std::endl;
    return -1;
}

if (!gl3wIsSupported(3, 3)) {
    std::cerr << "OpenGL Version 3.3 not supported" << std::endl;
    return -1;
}

init vbo and its index buffer, then vao, and the shader program, bind the vertex shader input to 0

glGenBuffers(2, vbo);

glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glBufferData(GL_ARRAY_BUFFER, 8*sizeof(GLfloat), square, GL_STATIC_DRAW);

glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
glBufferData(GL_ARRAY_BUFFER, 4*sizeof(GLushort), indices, GL_STATIC_DRAW);

glGenVertexArrays(1, &vao);
glBindVertexArray(vao);

program = glCreateProgram();

GLuint vertex_shader, fragment_shader;

loadShader_FILE(vertex_shader, "shader/default.vsh", GL_VERTEX_SHADER);
glAttachShader(program, vertex_shader);

loadShader_FILE(fragment_shader, "shader/default.fsh", GL_FRAGMENT_SHADER);
glAttachShader(program, fragment_shader);

glBindAttribLocation(program, 0, "pos");

glLinkProgram(program);

start rendering

glUseProgram(program);

glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glVertexAttribPointer(
            0,
            2,
            GL_FLOAT,
            GL_FALSE,
            sizeof(GLfloat)*2,
            (void*)0);
glEnableVertexAttribArray(0);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo[1]);
glDrawElements(
            GL_TRIANGLE_STRIP,
            4,
            GL_UNSIGNED_SHORT,
            (void*)0);

glDisableVertexAttribArray(0);
glfwSwapBuffers(window);

vertex shader

#version 330
in vec2 pos;
out vec2 c;

void main(void)
{
    gl_Position = vec4(pos, 0.0, 1.0);
    c = (pos+1)*0.5;
}

fragment shader

#version 330
in vec2 c;
out vec4 color;

void main(void)
{
    color = vec4(c, 1, 1);
}

the shaders compile without errors, apitrace can't find any opengl errors

1
c++openglglsl
Shouldn't the glfwSwapBuffers(window); call placed inside a loop, like here. Also it might be possible, if you changed you graphic card settings sometimes before, that some features are not allowed to increase the performance. For example you can deactivate anti aliasing in your graphic card control panel to increase the fps amount. As a result of such a change your program is not able to use the anti aliasing feature and maybe can't display your renders. And last but not least your graphic card doesn't support the opengl 3.3. That's all i know. :-) - Sascha
Your vertex order is wrong to draw a quad with GL_TRIANGLE_STRIP. You'll have to swap the 3rd and 4th vertex. But that would just cause it to render wrong, not stop it from rendering anything at all. So I don't think it's your main problem. I didn't spot any other problems reading through the code. - Reto Koradi
const GLfloat indices[4] = { 0, 1, 2, 3 }; should be const GLushort indices[4] = { 0, 1, 2, 3 }; - user2798943

1 Answers

2
votes

Well, this cannot be good:

const GLfloat indices[4] = { 0, 1, 2, 3 };

You told OpenGL that those were unsigned shorts, but they are floating-point. Nevermind the fact that GLfloat is twice the size of GLushort, the way those numbers are represented is very different. Floating-point vertex indices do not make a whole lot of sense.

Instead, you should use:

const GLushort indices[4] = { 0, 1, 2, 3 };