frag.glsl

#version 330
out vec4 out_color;
void main() {
  out_color = vec4(1.0f, 0.0f, 0.0f, 0.0f);
}

vert.glsl

#version 330
in vec2 position;
void main() {
  gl_Position = vec4(position, 0.0, 1.0f);
}