1 files changed, 146 insertions, 0 deletions
diff --git a/libqpdf/Pl_PNGFilter.cc b/libqpdf/Pl_PNGFilter.cc
new file mode 100644
index 00000000..28b87c5e
--- /dev/null
+++ b/libqpdf/Pl_PNGFilter.cc
@@ -0,0 +1,146 @@
+
+#include <qpdf/Pl_PNGFilter.hh>
+#include <string.h>
+
+Pl_PNGFilter::Pl_PNGFilter(char const* identifier, Pipeline* next,
+			   action_e action, unsigned int columns,
+			   unsigned int bytes_per_pixel) :
+    Pipeline(identifier, next),
+    action(action),
+    columns(columns),
+    cur_row(0),
+    prev_row(0),
+    buf1(0),
+    buf2(0),
+    pos(0)
+{
+    this->buf1 = new unsigned char[columns + 1];
+    this->buf2 = new unsigned char[columns + 1];
+    this->cur_row = buf1;
+
+    // number of bytes per incoming row
+    this->incoming = (action == a_encode ? columns : columns + 1);
+}
+
+Pl_PNGFilter::~Pl_PNGFilter()
+{
+    delete [] buf1;
+    delete [] buf2;
+}
+
+void
+Pl_PNGFilter::write(unsigned char* data, int len)
+{
+    int left = this->incoming - this->pos;
+    unsigned int 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;
+	memset(this->cur_row, 0, this->columns + 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 = (int) this->cur_row[0];
+    if (this->prev_row)
+    {
+	switch (filter)
+	{
+	  case 0:			// none
+	    break;
+
+	  case 1:			// sub
+	    throw Exception("sub filter not implemented");
+	    break;
+
+	  case 2:			// up
+	    for (unsigned int i = 1; i <= this->columns; ++i)
+	    {
+		this->cur_row[i] += this->prev_row[i];
+	    }
+	    break;
+
+	  case 3:			// average
+	    throw Exception("average filter not implemented");
+	    break;
+
+	  case 4:			// Paeth
+	    throw Exception("Paeth filter not implemented");
+	    break;
+
+	  default:
+	    // ignore
+	    break;
+	}
+    }
+
+    getNext()->write(this->cur_row + 1, this->columns);
+}
+
+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->columns; ++i)
+	{
+	    ch = this->cur_row[i] - this->prev_row[i];
+	    getNext()->write(&ch, 1);
+	}
+    }
+    else
+    {
+	getNext()->write(this->cur_row, this->columns);
+    }
+}
+
+void
+Pl_PNGFilter::finish()
+{
+    if (this->pos)
+    {
+	// write partial row
+	processRow();
+    }
+    this->prev_row = 0;
+    this->cur_row = buf1;
+    this->pos = 0;
+    memset(this->cur_row, 0, this->columns + 1);
+
+    getNext()->finish();
+}