### Compilation failed:

error: 1: invalid type
layout(binding=0) uniform sampler2D tex;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: 3: 'main' must return: 'vec4', 'float4', or 'half4'
void main() {
^^^^^^^^^^^
error: 4: unknown identifier 'sample'
    float4 a = sample(tex, float2(0));
               ^^^^^^
error: 5: unknown identifier 'sample'
    float4 b = sample(tex, float3(0));
               ^^^^^^
error: 6: unknown identifier 'sk_FragColor'
    sk_FragColor = half4(float2(a.xy), float2(b.zw));
    ^^^^^^^^^^^^
error: 6: unknown identifier 'a'
    sk_FragColor = half4(float2(a.xy), float2(b.zw));
                                ^
error: 6: unknown identifier 'b'
    sk_FragColor = half4(float2(a.xy), float2(b.zw));
                                              ^
7 errors