opengl 3.3 core profile render fails - c++

Question

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

Answer 1

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 };