### Compilation failed:

error: 1: 'main' must return: 'vec4', 'float4', or 'half4'
void main() {
^^^^^^^^^^^
error: 2: unknown identifier 'sk_FragColor'
    sk_FragColor = half4(sk_Clockwise ? +1 : -1);
    ^^^^^^^^^^^^
error: 2: unknown identifier 'sk_Clockwise'
    sk_FragColor = half4(sk_Clockwise ? +1 : -1);
                         ^^^^^^^^^^^^
3 errors