glDrawElements doesn't render anything - c++

Question

I want to draw simple square. First I use glDrawArrays but now I want to change it to glDrawElements. I read bunch of tutorials but for some reason it doesn't render anything.
Renderer class:
class Renderer_t {
private:
...
glm::mat4 projectionMatrix; // Store the projection matrix
glm::mat4 viewMatrix; // Store the view matrix
glm::mat4 modelMatrix; // Store the model matrix
unsigned int vaoID[1]; // Our Vertex Array Object
unsigned int vboID[3]; // Our Vertex Buffer Object
...
};
Initialize of scene:
Renderer_t::Renderer_t(SDL_Window* window): scene(nullptr), width(800), height(600) {
LOG(info) << "Renderer_t constructor";
gl = SDL_GL_CreateContext(window);
glbinding::Binding::initialize();
//Initialize scene
glClearColor(0.4f, 0.6f, 0.9f, 0.0f);
shader = new Shader("../assets/shader.vert", "../assets/shader.frag");
float ratio = width/height;
projectionMatrix = glm::perspective(60.0f, ratio, 0.1f, 100.f); // Create our perspective projection matrix
int vertnum = 4 * 3; //6x
//Create square
float* vertices = new float[vertnum]; // Vertices for our square
float* colors = new float[vertnum]; // Colors for our vertices
unsigned int* indices = new unsigned int[6];
indices[0] = 0; indices[0] = 1; indices[0] = 2;
indices[0] = 2; indices[0] = 3; indices[0] = 0;
vertices[0] = -0.5; vertices[1] = -0.5; vertices[2] = 0.0; // Bottom left corner
colors[0] = 1.0; colors[1] = 1.0; colors[2] = 1.0; // Bottom left corner
vertices[3] = -0.5; vertices[4] = 0.5; vertices[5] = 0.0; // Top left corner
colors[3] = 1.0; colors[4] = 0.0; colors[5] = 0.0; // Top left corner
vertices[6] = 0.5; vertices[7] = 0.5; vertices[8] = 0.0; // Top Right corner
colors[6] = 0.0; colors[7] = 1.0; colors[8] = 0.0; // Top Right corner
vertices[9] = 0.5; vertices[10] = -0.5; vertices[11] = 0.0; // Bottom right corner
colors[9] = 0.0; colors[10] = 0.0; colors[11] = 1.0; // Bottom right corner
/*
vertices[12] = -0.5; vertices[13] = -0.5; vertices[14] = 0.0; // Bottom left corner
colors[12] = 1.0; colors[13] = 1.0; colors[14] = 1.0; // Bottom left corner
vertices[15] = 0.5; vertices[16] = 0.5; vertices[17] = 0.0; // Top Right corner
colors[15] = 0.0; colors[16] = 1.0; colors[17] = 0.0; // Top Right corner
*/
glGenVertexArrays(1, &vaoID[0]); // Create our Vertex Array Object
glBindVertexArray(vaoID[0]); // Bind our Vertex Array Object so we can use it
glGenBuffers(3, &vboID[0]); // Generate our Vertex Buffer Objects
glBindBuffer(GL_ARRAY_BUFFER, vboID[0]); // Bind our Vertex Buffer Object
glBufferData(GL_ARRAY_BUFFER, vertnum * sizeof(GLfloat), vertices, GL_STATIC_DRAW); // Set the size and data of our VBO and set it to STATIC_DRAW
glVertexAttribPointer((GLuint)0, 3, GL_FLOAT, GL_FALSE, 0, 0); // Set up our vertex attributes pointer
glEnableVertexAttribArray(0); // Enable our Vertex Array Object
glBindBuffer(GL_ARRAY_BUFFER, vboID[1]); // Bind our second Vertex Buffer Object
glBufferData(GL_ARRAY_BUFFER, vertnum * sizeof(GLfloat), colors, GL_STATIC_DRAW); // Set the size and data of our VBO and set it to STATIC_DRAW
glVertexAttribPointer((GLuint)1, 3, GL_FLOAT, GL_FALSE, 0, 0); // Set up our vertex attributes pointer
glEnableVertexAttribArray(1); // Enable the second vertex attribute array
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboID[2]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(GLuint), indices, GL_STATIC_DRAW);
glVertexAttribPointer((GLuint)2, 3, GL_INT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(2);
glBindVertexArray(0); // Disable our Vertex Buffer Object
delete[] vertices; // Delete our vertices from memory
delete[] colors; // Delete our vertices from memory
delete[] indices;
LOG(info) << "Renderer_t constructor done";
}
Rendering:
void Renderer_t::render() {
LOG(info) << "Renderer_t.render()";
glViewport(0, 0, width, height); // Set the viewport size to fill the window
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT); // Clear required buffers
viewMatrix = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, 0.0f, -5.f)); // Create our view matrix
modelMatrix = glm::scale(glm::mat4(1.0f), glm::vec3(1.0f)); // Create our model matrix
shader->bind(); // Bind our shader
int projectionMatrixLocation = glGetUniformLocation(shader->id(), "projectionMatrix"); // Get the location of our projection matrix in the shader
int viewMatrixLocation = glGetUniformLocation(shader->id(), "viewMatrix"); // Get the location of our view matrix in the shader
int modelMatrixLocation = glGetUniformLocation(shader->id(), "modelMatrix"); // Get the location of our model matrix in the shader
glUniformMatrix4fv(projectionMatrixLocation, 1, GL_FALSE, &projectionMatrix[0][0]); // Send our projection matrix to the shader
glUniformMatrix4fv(viewMatrixLocation, 1, GL_FALSE, &viewMatrix[0][0]); // Send our view matrix to the shader
glUniformMatrix4fv(modelMatrixLocation, 1, GL_FALSE, &modelMatrix[0][0]); // Send our model matrix to the shader
glBindVertexArray(vaoID[0]); // Bind our Vertex Array Object
// glDrawArrays(GL_TRIANGLES, 0, 6); // Draw our square
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboID[2]);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, NULL);
glBindVertexArray(0); // Unbind our Vertex Array Object
shader->unbind(); // Unbind our shader
LOG(info) << "Renderer_t.render() done";
}
I also use shaders:
shader.vert
version 130
uniform mat4 projectionMatrix;
uniform mat4 viewMatrix;
uniform mat4 modelMatrix;
in vec3 in_Position;
in vec3 in_Color;
out vec3 pass_Color;
void main(void)
{
gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4(in_Position, 1.0);
pass_Color = in_Color;
}
shader.fraq
#version 130
in vec3 pass_Color;
out vec4 out_Color;
void main(void)
{
out_Color = vec4(pass_Color, 1.0);
}

Answer 1

Just so you know, a triangle list with elements: 0,1,2 0,2,3 is the same thing as glDrawArrays(GL_TRIANGLE_FAN, 0, 4). You could just use a triangle fan here and not have to use indices at all.
Your actual problem is that you keep writing each element in your element array to [0].
Right now your code reads:
indices[0] = 0; indices[0] = 1; indices[0] = 2;
indices[0] = 2; indices[0] = 3; indices[0] = 0;
However, to function correctly it needs to read:
indices[0] = 0; indices[1] = 1; indices[2] = 2;
indices[3] = 2; indices[4] = 3; indices[5] = 0; // This is equivalent to 0, 2, 3
Everything in BDL's answer are also important things you should note.

Answer 2

You try to bind the ELEMENT_ARRAY_BUFFER to a varying of your shader
glVertexAttribPointer((GLuint)2, 3, GL_INT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(2);
Index buffers do not have to be bound to a shader, since they are not directly used as input to them. Beside this, your shader has only two in-variables (most probably numbered 0 and 1), so using 2 will never work.
Another hint:
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboID[2]);
in your render() is not necessary, since the binding is already stored in the vao during the initialization. But this should not effect the output.