#version 460

vec2 positions [3] = vec2 [] (
                              vec2 ( 0.0, -0.5),
                              vec2 ( 0.5,  0.5),
                              vec2 (-0.5, -0.5)
                             );

void main () {
  gl_Position = vec4 (positions [gl_VertexIndex], 0.0, 1.0);
}