skia2/resources/sksl/runtime/VectorIndexing.rts

uniform float4 u1;
float index_by_literal() {
    return u1[0];
}

uniform float4 u2;
float index_by_loop() {
    float sum = 0;
    for (int i = 0; i < 4; ++i) {
        sum += u2[i];
    }
    return sum;
}

uniform float4 u3;
float index_by_complex_loop() {
    float prod = 1;
    for (int i = 0; i < 4; ++i) {
        prod *= u3[i < 2 ? 0 : i];
    }
    return prod;
}

uniform float4 u4;
float index_clamped_out_of_bounds() {
    for (int i = 7; i < 8; i++) {
        return u4[i];
    }
}

float4 main(float2 xy) {
    return float4(
        index_by_literal(),
        index_by_loop(),
        index_by_complex_loop(),
        index_clamped_out_of_bounds());
}