1### Compilation failed: 2 3error: 5: 'main' must return: 'vec4', 'float4', or 'half4' 4void main() { 5^^^^^^^^^^^ 6error: 6: unknown identifier 'sk_FragColor' 7 sk_FragColor.x = cross_length_2d(ah, bh); 8 ^^^^^^^^^^^^ 9error: 6: unknown identifier 'cross_length_2d' 10 sk_FragColor.x = cross_length_2d(ah, bh); 11 ^^^^^^^^^^^^^^^ 12error: 7: unknown identifier 'sk_FragColor' 13 sk_FragColor.y = half(cross_length_2d(af, bf)); 14 ^^^^^^^^^^^^ 15error: 7: unknown identifier 'cross_length_2d' 16 sk_FragColor.y = half(cross_length_2d(af, bf)); 17 ^^^^^^^^^^^^^^^ 185 errors 19