The Annoyance Filter.pdf - Fourmilab

86 FLASH STREAM DECODER ANNOYANCE-FILTER §107
107. A transformation matrix is stored as separate scale, rotation/skew, and translation terms, each
represented as a signed fixed-point value. The scale and rotation/skew terms are optional and are
omitted if they are identity—an initial bit indicates whether they are present.
〈 Class implementations 11 〉 +≡
void flashStream ::getMatrix (matrix ∗ mat )
{
initBits ( ); /∗ Scale terms ∗/
if (getBits (1)) {
int nBits = static cast〈int〉(getBits (5));
}
mat ⃗ a = getSignedBits (nBits );
mat ⃗ d = getSignedBits (nBits );
}
else {
mat ⃗ a = mat ⃗ d = # 00010000 L ; /∗ Identity: omitted ∗/
} /∗ Rotate/skew terms ∗/
if (getBits (1)) {
int nBits = static cast〈int〉(getBits (5));
mat ⃗ b = getSignedBits (nBits );
mat ⃗ c = getSignedBits (nBits );
}
else {
mat ⃗ b = mat ⃗ c = 0; /∗ Identity: omitted ∗/
} /∗ Translate terms ∗/
int nBits = static cast〈int〉(getBits (5));
mat ⃗ tx = getSignedBits (nBits );
mat ⃗ ty = getSignedBits (nBits );