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#include <qpdf/Pl_PNGFilter.hh>
#include <qpdf/QTC.hh>
#include <qpdf/QUtil.hh>
#include <limits.h>
#include <stdexcept>
#include <string.h>
static int
abs_diff(int a, int b)
{
return a > b ? a - b : b - a;
}
Pl_PNGFilter::Pl_PNGFilter(
char const* identifier,
Pipeline* next,
action_e action,
unsigned int columns,
unsigned int samples_per_pixel,
unsigned int bits_per_sample) :
Pipeline(identifier, next),
action(action),
cur_row(nullptr),
prev_row(nullptr),
buf1(nullptr),
buf2(nullptr),
pos(0)
{
if (samples_per_pixel < 1) {
throw std::runtime_error(
"PNGFilter created with invalid samples_per_pixel");
}
if (!((bits_per_sample == 1) || (bits_per_sample == 2) ||
(bits_per_sample == 4) || (bits_per_sample == 8) ||
(bits_per_sample == 16))) {
throw std::runtime_error(
"PNGFilter created with invalid bits_per_sample not"
" 1, 2, 4, 8, or 16");
}
this->bytes_per_pixel = ((bits_per_sample * samples_per_pixel) + 7) / 8;
unsigned long long bpr =
((columns * bits_per_sample * samples_per_pixel) + 7) / 8;
if ((bpr == 0) || (bpr > (UINT_MAX - 1))) {
throw std::runtime_error(
"PNGFilter created with invalid columns value");
}
this->bytes_per_row = bpr & UINT_MAX;
this->buf1 =
QUtil::make_shared_array<unsigned char>(this->bytes_per_row + 1);
this->buf2 =
QUtil::make_shared_array<unsigned char>(this->bytes_per_row + 1);
memset(this->buf1.get(), 0, this->bytes_per_row + 1);
memset(this->buf2.get(), 0, this->bytes_per_row + 1);
this->cur_row = this->buf1.get();
this->prev_row = this->buf2.get();
// number of bytes per incoming row
this->incoming =
(action == a_encode ? this->bytes_per_row : this->bytes_per_row + 1);
}
void
Pl_PNGFilter::write(unsigned char const* data, size_t len)
{
size_t left = this->incoming - this->pos;
size_t offset = 0;
while (len >= left) {
// finish off current row
memcpy(this->cur_row + this->pos, data + offset, left);
offset += left;
len -= left;
processRow();
// Swap rows
unsigned char* t = this->prev_row;
this->prev_row = this->cur_row;
this->cur_row = t ? t : this->buf2.get();
memset(this->cur_row, 0, this->bytes_per_row + 1);
left = this->incoming;
this->pos = 0;
}
if (len) {
memcpy(this->cur_row + this->pos, data + offset, len);
}
this->pos += len;
}
void
Pl_PNGFilter::processRow()
{
if (this->action == a_encode) {
encodeRow();
} else {
decodeRow();
}
}
void
Pl_PNGFilter::decodeRow()
{
int filter = this->cur_row[0];
if (this->prev_row) {
switch (filter) {
case 0:
break;
case 1:
this->decodeSub();
break;
case 2:
this->decodeUp();
break;
case 3:
this->decodeAverage();
break;
case 4:
this->decodePaeth();
break;
default:
// ignore
break;
}
}
getNext()->write(this->cur_row + 1, this->bytes_per_row);
}
void
Pl_PNGFilter::decodeSub()
{
QTC::TC("libtests", "Pl_PNGFilter decodeSub");
unsigned char* buffer = this->cur_row + 1;
unsigned int bpp = this->bytes_per_pixel;
for (unsigned int i = 0; i < this->bytes_per_row; ++i) {
unsigned char left = 0;
if (i >= bpp) {
left = buffer[i - bpp];
}
buffer[i] = static_cast<unsigned char>(buffer[i] + left);
}
}
void
Pl_PNGFilter::decodeUp()
{
QTC::TC("libtests", "Pl_PNGFilter decodeUp");
unsigned char* buffer = this->cur_row + 1;
unsigned char* above_buffer = this->prev_row + 1;
for (unsigned int i = 0; i < this->bytes_per_row; ++i) {
unsigned char up = above_buffer[i];
buffer[i] = static_cast<unsigned char>(buffer[i] + up);
}
}
void
Pl_PNGFilter::decodeAverage()
{
QTC::TC("libtests", "Pl_PNGFilter decodeAverage");
unsigned char* buffer = this->cur_row + 1;
unsigned char* above_buffer = this->prev_row + 1;
unsigned int bpp = this->bytes_per_pixel;
for (unsigned int i = 0; i < this->bytes_per_row; ++i) {
int left = 0;
int up = 0;
if (i >= bpp) {
left = buffer[i - bpp];
}
up = above_buffer[i];
buffer[i] = static_cast<unsigned char>(buffer[i] + (left + up) / 2);
}
}
void
Pl_PNGFilter::decodePaeth()
{
QTC::TC("libtests", "Pl_PNGFilter decodePaeth");
unsigned char* buffer = this->cur_row + 1;
unsigned char* above_buffer = this->prev_row + 1;
unsigned int bpp = this->bytes_per_pixel;
for (unsigned int i = 0; i < this->bytes_per_row; ++i) {
int left = 0;
int up = above_buffer[i];
int upper_left = 0;
if (i >= bpp) {
left = buffer[i - bpp];
upper_left = above_buffer[i - bpp];
}
buffer[i] = static_cast<unsigned char>(
buffer[i] + this->PaethPredictor(left, up, upper_left));
}
}
int
Pl_PNGFilter::PaethPredictor(int a, int b, int c)
{
int p = a + b - c;
int pa = abs_diff(p, a);
int pb = abs_diff(p, b);
int pc = abs_diff(p, c);
if (pa <= pb && pa <= pc) {
return a;
}
if (pb <= pc) {
return b;
}
return c;
}
void
Pl_PNGFilter::encodeRow()
{
// For now, hard-code to using UP filter.
unsigned char ch = 2;
getNext()->write(&ch, 1);
if (this->prev_row) {
for (unsigned int i = 0; i < this->bytes_per_row; ++i) {
ch = static_cast<unsigned char>(
this->cur_row[i] - this->prev_row[i]);
getNext()->write(&ch, 1);
}
} else {
getNext()->write(this->cur_row, this->bytes_per_row);
}
}
void
Pl_PNGFilter::finish()
{
if (this->pos) {
// write partial row
processRow();
}
this->prev_row = nullptr;
this->cur_row = buf1.get();
this->pos = 0;
memset(this->cur_row, 0, this->bytes_per_row + 1);
getNext()->finish();
}
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