/*
* Converts a 16-bit RGB pixel to grayscale, as specified in ITU BT.601.
*/
static void
opng_reset_chroma16_bt601(png_bytep rgb16)
{
/* Use 16-bit multiplications and 32-bit additions. */
unsigned int r16 = png_get_uint_16(rgb16 + 0);
unsigned int g16 = png_get_uint_16(rgb16 + 2);
unsigned int b16 = png_get_uint_16(rgb16 + 4);
png_uint_32 r32 = r16 * (png_uint_32)Kr_bt601;
png_uint_32 g32 = g16 * (png_uint_32)Kg_bt601;
png_uint_32 b32 = b16 * (png_uint_32)Kb_bt601;
png_uint_32 y32 = r32 + g32 + b32;
unsigned int y16 = (unsigned int)((y32 + 32767U) / 65535U);
png_save_uint_16(rgb16 + 0, y16);
png_save_uint_16(rgb16 + 2, y16);
png_save_uint_16(rgb16 + 4, y16);
}
/*
* Sets the precision of a 16-bit sample to a lower value,
* then scales the result back to 16 bits.
*/
static void
opng_set_precision16(png_bytep sample_ptr, int new_precision)
{
unsigned int old_value = png_get_uint_16(sample_ptr);
unsigned int chop_value = old_value >> (16 - new_precision);
unsigned int chop_max = (1U << new_precision) - 1;
unsigned int new_value =
(unsigned int)
(((png_uint_32)chop_value * 65535U + chop_max / 2) / chop_max);
png_save_uint_16(sample_ptr, new_value);
}
/*
* @brief manually process a single chunk of apng data
*/
void apng_ani::_process_chunk()
{
_id = _read_chunk(_chunk);
if (_id == id_acTL && !_got_IDAT && !_got_acTL) {
// animation control chunk
if (!_reading) {
return;
}
nframes = png_get_uint_32(&_chunk.data[8]);
plays = png_get_uint_32(&_chunk.data[12]);
if (!nframes || nframes > PNG_UINT_31_MAX || plays > PNG_UINT_31_MAX) {
_apng_failed("invalid apng acTL data");
}
_got_acTL = true;
_frames.reserve(nframes);
_frame_offsets.reserve(nframes+1); // extra 1 is for EOF offset
}
else if (_id == id_fcTL && (!_got_IDAT || _got_acTL)) {
// frame control chunk
if (_reading) {
uint sequence_num = png_get_uint_32(&_chunk.data[8]);
if (sequence_num != _sequence_num++) {
_apng_failed("invalid apng fcTL sequence number");
}
}
// handle frame finish in next_frame
_framew = png_get_uint_32(&_chunk.data[12]);
_frameh = png_get_uint_32(&_chunk.data[16]);
_x_offset = png_get_uint_32(&_chunk.data[20]);
_y_offset = png_get_uint_32(&_chunk.data[24]);
_delay_num = png_get_uint_16(&_chunk.data[28]);
_delay_den = png_get_uint_16(&_chunk.data[30]);
_dispose_op = _chunk.data[32];
_blend_op = _chunk.data[33];
if (_reading &&
(_framew > cMaxPNGSize || _frameh > cMaxPNGSize
|| _x_offset > cMaxPNGSize || _y_offset > cMaxPNGSize
|| _x_offset + _framew > w || _y_offset + _frameh > h
|| _dispose_op > 2 || _blend_op > 1)) {
_apng_failed("invalid apng fcTL data");
}
// according to spec...
if (current_frame == 0 && _dispose_op == 2) {
_dispose_op = 1;
}
if (_delay_den == 0) _delay_den = 100; // APNG spec
if (_delay_num == 0) _delay_num = 1; // arbitrary lower bound
float frame_delay = static_cast<float>(_delay_num)/static_cast<float>(_delay_den);
frame.delay = frame_delay;
if (_reading) {
anim_time+= frame_delay;
_frame_offsets.push_back((int)_offset);
}
else {
if (_got_IDAT && _processing_start()) {
_apng_failed("couldn't start fdat apng frame");
}
}
}
else if (_id == id_IDAT) {
_got_IDAT = true;
_processing_data(&_chunk.data[0], _chunk.size);
}
else if (_id == id_fdAT && _got_acTL) {
if (_reading) {
uint sequence_num = png_get_uint_32(&_chunk.data[8]);
if (sequence_num != _sequence_num++) {
_apng_failed("invalid apng fdAT sequence number");
}
}
if (_reading) {
return;
}
png_save_uint_32(&_chunk.data[4], _chunk.size - 16);
memcpy(&_chunk.data[8], "IDAT", 4);
_processing_data(&_chunk.data[4], _chunk.size - 4);
}
else if (_id == id_IEND) {
return;
}
else if (not_chunk(_chunk.data[4]) || not_chunk(_chunk.data[5]) ||
not_chunk(_chunk.data[6]) || not_chunk(_chunk.data[7])) {
_apng_failed("unknown chunk ID found");
}
else if (!_got_IDAT) {
_processing_data(&_chunk.data[0], _chunk.size);
_info_chunks.push_back(_chunk);
}
}
