#version 450

// iter3 fullscreen triangle vertex shader.
// Emits 3 vertices from gl_VertexIndex that cover NDC -1..1 with one big triangle.
//   idx=0: NDC (-1,-1)   — top-left in Vulkan
//   idx=1: NDC ( 3,-1)   — far-right (off-screen)
//   idx=2: NDC (-1, 3)   — far-bottom (off-screen)
// The visible portion of the triangle covers the full viewport.

void main() {
    vec2 pos = vec2((gl_VertexIndex << 1) & 2, gl_VertexIndex & 2);
    gl_Position = vec4(pos * 2.0 - 1.0, 0.0, 1.0);
}