OpenGL rendering black square - c++

Question

I am attempting to render a colored rectangle, but I just end up with a black one.
My shaders and shader program do not produce any errors when compiling or linking, so I am sure there is something going wrong when I am attempting to buffer the data. But, everything looks correct to me.
Shader sources
std::string const fragment_shader_source = "#version 330 core\n"
""
"in vec4 fColor;\n"
"\n"
"out vec4 finalColor;\n"
"\n"
"void main() {\n"
" finalColor = fColor;\n"
"}";
std::string const vertex_shader_source = "#version 330 core\n"
""
"layout (location = 0) in vec2 vPos;\n"
"layout (location = 1) in vec4 vColor;\n"
"\n"
"out vec4 fColor;\n"
"void main() {\n"
" gl_Position = vec4(vPos.xy, 1.0, 1.0);\n"
" fColor = vColor;\n"
"}";
Vertex data
static GLfloat const vertex_data[] = {
// //Position //Color //UV Coords
0.5f, 0.5f, 1.0f, 0.0f, 1.0f, 1.0f,
-0.5f, 0.5f, 1.0f, 0.0f, 0.0f, 1.0f,
0.5f, -0.5f, 1.0f, 1.0f, 0.0f, 1.0f,
-0.5f, -0.5f, 0.0f, 1.0f, 1.0f, 1.0f,
-0.5f, 0.5f, 0.0f, 0.0f, 1.0f, 1.0f,
0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 1.0f
};
Here is my main loop:
int SDLApp::AppMain(int argc, char** argv) {
if(sdl_window_ == nullptr) {
acorn::Log(acorn::LoggingLevel::Fatal, "Could not initialize the window.");
return -1;
}
if(sdl_gl_context_ == nullptr) {
acorn::Log(acorn::LoggingLevel::Fatal, "Could not create an OpenGL context.");
return -1;
}
acorn::shader::FragmentShader f(fragment_shader_source);
acorn::shader::VertexShader v(vertex_shader_source);
acorn::shader::Program shader_program(f, v);
shader_program.Link();
shader_program.Use();
GLuint vao_;
glGenVertexArrays(1, &vao_);
GLuint vbo_;
glGenBuffers(1, &vbo_);
glBindVertexArray(vao_);
glBindBuffer(GL_ARRAY_BUFFER, vbo_);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (void*)0);
glEnableVertexAttribArray(1);
glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (void*)2);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(GLfloat) * 6, vertex_data, GL_STATIC_DRAW);
glClearColor(1.0f, 0.0f, 0.0f,1.0f);
SDL_Event event;
while (true) {
while (SDL_PollEvent(&event)) {
if (event.type == SDL_QUIT) {
return 0;
}
}
glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 6);
SDL_GL_SwapWindow(sdl_window_);
}
}

Answer 1

The last parameter of glVertexAttribPointer is treated as a byte offset into the buffer object's data store.
So the offset has to be 8, 2*sizeof(float):
glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 6*sizeof(GLfloat),
(void*)(2*sizeof(GLfloat)));
After changing that, your code works fine