sksl/shared/MatrixSwizzleStore.sksl

uniform half4 colorGreen, colorRed;
uniform float3x3 testMatrix3x3;
uniform float4x4 testMatrix4x4;

bool test3x3() {
    float3x3 matrix;
    float3 values = float3(3, 2, 1);
    for (int index=0; index<3; ++index) {
        matrix[index].zx = values.xz;
        matrix[index].y = values.y;
        values += 3;
    }
    return matrix == testMatrix3x3;
}

bool test4x4() {
    float4x4 matrix;
    float4 values = float4(4, 3, 2, 1);
    for (int index=0; index<4; ++index) {
        matrix[index].wx = values.xw;
        matrix[index].zy = values.yz;
        values += 4;
    }
    return matrix == testMatrix4x4;
}

half4 main(float2 coords) {
    return test3x3() && test4x4() ? colorGreen : colorRed;
}