#version 440

out vec2 uv;
out vec3 normal;

uniform mat4 uTransform;
uniform sampler2D uHeightmap;

const int num_verts = 511;
const float scale = 1.0 / num_verts;

vec2[] offsets = vec2[](
    vec2(0,0),
    vec2(1,0),
    vec2(1,1),
    vec2(0,0),
    vec2(0,1),
    vec2(1,1)
);

void main()
{
    int idx = gl_VertexID / 6;
    int off = gl_VertexID % 6;

    int x = idx / num_verts;
    int y = idx % num_verts;

    vec2 pos = vec2(float(x), float(y)) + offsets[off];
    uv = scale * pos;

    float h = texture(uHeightmap, uv).x;
    gl_Position = uTransform * vec4(pos.x, h, pos.y, 1);
}