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Add matrix and annotation appearance stream handling

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Generate page content fragment for rendering appearance streams
including all matrix calculation.
This commit is contained in:
Jay Berkenbilt 2018-12-24 17:54:48 -05:00
parent 5059ec0d35
commit 104fd6da52
2 changed files with 210 additions and 0 deletions
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18
include/qpdf/QPDFAnnotationObjectHelper.hh
View File

@ -72,6 +72,24 @@ class QPDFAnnotationObjectHelper: public QPDFObjectHelper
QPDFObjectHandle getAppearanceStream(std::string const& which,
std::string const& state = "");
// Return a matrix that transforms from the annotation's
// appearance stream's coordinates to the page's coordinates. This
// method also honors the annotation's NoRotate flag if set. The
// matrix is returned as a string representing the six floating
// point numbers to be passed to a cm operator. Returns the empty
// string if it is unable to compute the matrix for any reason.
// The value "rotate" should be set to the page's /Rotate value or
// 0 if none.
QPDF_DLL
std::string getAnnotationAppearanceMatrix(int rotate);
// Generate text suitable for addition to the containing page's
// content stream that replaces this annotation's appearance
// stream. The value "rotate" should be set to the page's /Rotate
// value or 0 if none.
QPDF_DLL
std::string getPageContentForAppearance(int rotate);
private:
class Members
{

192
libqpdf/QPDFAnnotationObjectHelper.cc
View File

@ -1,5 +1,10 @@
#include <qpdf/QPDFAnnotationObjectHelper.hh>
#include <qpdf/QTC.hh>
#include <qpdf/QPDFMatrix.hh>
#include <qpdf/QUtil.hh>
#include <qpdf/QPDF.hh>
#include <qpdf/QPDFNameTreeObjectHelper.hh>
#include <algorithm>
QPDFAnnotationObjectHelper::Members::~Members()
{
@ -73,3 +78,190 @@ QPDFAnnotationObjectHelper::getAppearanceStream(
QTC::TC("qpdf", "QPDFAnnotationObjectHelper AN null");
return QPDFObjectHandle::newNull();
}
std::string
QPDFAnnotationObjectHelper::getAnnotationAppearanceMatrix(int rotate)
{
// The appearance matrix is the transformation in effect when
// rendering an appearance stream's content. The appearance stream
// itself is a form XObject, which has a /BBox and an optional
// /Matrix. The /BBox describes the bounding box of the annotation
// in unrotated page coordinates. /Matrix may be applied to the
// bounding box to transform the bounding box. The effect of this
// is that the transformed box is still fit within the area the
// annotation designates in its /Rect field.
// The algorithm for computing the appearance matrix described in
// section 12.5.5 of the ISO-32000 PDF spec. It is as follows:
// 1. Transform the four corners of /BBox by applying /Matrix to
// them, creating an arbitrarily transformed quadrilateral.
// 2. Find the minimum upright rectangle that encompasses the
// resulting quadrilateral. This is the "transformed appearance
// box", T.
// 3. Compute matrix A that maps the lower left and upper right
// corners of T to the annotation's /Rect. This can be done by
// translating the lower left corner and then scaling so that
// the upper right corner also matches.
// 4. Concatenate /Matrix to A to get matrix AA. This matrix
// translates from appearance stream coordinates to page
// coordinates.
// If the annotation's /F flag has bit 4 set, we modify the matrix
// to also rotate the annotation in the opposite direction, and we
// adjust the destination rectangle by rotating it about the upper
// left hand corner so that the annotation will appear upright on
// the rotated page.
// You can see that the above algorithm works by imagining the
// following:
// * In the simple case of where /BBox = /Rect and /Matrix is the
// identity matrix, the transformed quadrilateral in step 1 will
// be the bounding box. Since the bounding box is upright, T
// will be the bounding box. Since /BBox = /Rect, matrix A is
// the identity matrix, and matrix AA in step 4 is also the
// identity matrix.
//
// * Imagine that the rectangle is different from the bounding
// box. In this case, matrix A just transforms the bounding box
// to the rectangle by scaling and translating, effectively
// squeezing or stretching it into /Rect.
//
// * Imagine that /Matrix rotates the annotation by 30 degrees.
// The transformed bounding box would stick out, and T would be
// too big. In this case, matrix A shrinks T down until it fits
// in /Rect.
QPDFObjectHandle rect_obj = this->oh.getKey("/Rect");
QPDFObjectHandle flags = this->oh.getKey("/F");
QPDFObjectHandle as = getAppearanceStream("/N").getDict();
QPDFObjectHandle bbox_obj = as.getKey("/BBox");
QPDFObjectHandle matrix_obj = as.getKey("/Matrix");
if (! (bbox_obj.isRectangle() && rect_obj.isRectangle()))
{
return "";
}
QPDFMatrix matrix;
if (matrix_obj.isMatrix())
{
/// QTC::TC("qpdf", "QPDFAnnotationObjectHelper explicit matrix");
matrix = QPDFMatrix(matrix_obj.getArrayAsMatrix());
}
else
{
/// QTC::TC("qpdf", "QPDFAnnotationObjectHelper default matrix");
}
QPDFObjectHandle::Rectangle rect = rect_obj.getArrayAsRectangle();
if (rotate && flags.isInteger() && (flags.getIntValue() & 16))
{
// If the the annotation flags include the NoRotate bit and
// the page is rotated, we have to rotate the annotation about
// its upper left corner by the same amount in the opposite
// direction so that it will remain upright in absolute
// coordinates. Since the semantics of /Rotate for a page are
// to rotate the page, while the effect of rotating using a
// transformation matrix is to rotate the coordinate system,
// the opposite directionality is explicit in the code.
QPDFMatrix mr;
mr.rotatex90(rotate);
mr.concat(matrix);
matrix = mr;
double rect_w = rect.urx - rect.llx;
double rect_h = rect.ury - rect.lly;
switch (rotate)
{
case 90:
/// QTC::TC("qpdf", "QPDFAnnotationObjectHelper rotate 90");
rect = QPDFObjectHandle::Rectangle(
rect.llx,
rect.ury,
rect.llx + rect_h,
rect.ury + rect_w);
break;
case 180:
/// QTC::TC("qpdf", "QPDFAnnotationObjectHelper rotate 180");
rect = QPDFObjectHandle::Rectangle(
rect.llx - rect_w,
rect.ury,
rect.llx,
rect.ury + rect_h);
break;
case 270:
/// QTC::TC("qpdf", "QPDFAnnotationObjectHelper rotate 270");
rect = QPDFObjectHandle::Rectangle(
rect.llx - rect_h,
rect.ury - rect_w,
rect.llx,
rect.ury);
break;
default:
// ignore
break;
}
}
// Transform bounding box by matrix to get T
QPDFObjectHandle::Rectangle bbox = bbox_obj.getArrayAsRectangle();
std::vector<double> bx(4);
std::vector<double> by(4);
matrix.transform(bbox.llx, bbox.lly, bx.at(0), by.at(0));
matrix.transform(bbox.llx, bbox.ury, bx.at(1), by.at(1));
matrix.transform(bbox.urx, bbox.lly, bx.at(2), by.at(2));
matrix.transform(bbox.urx, bbox.ury, bx.at(3), by.at(3));
// Find the transformed appearance box
double t_llx = *std::min_element(bx.begin(), bx.end());
double t_urx = *std::max_element(bx.begin(), bx.end());
double t_lly = *std::min_element(by.begin(), by.end());
double t_ury = *std::max_element(by.begin(), by.end());
if ((t_urx == t_llx) || (t_ury == t_lly))
{
// avoid division by zero
return "";
}
// Compute a matrix to transform the appearance box to the rectangle
QPDFMatrix AA;
AA.translate(rect.llx, rect.lly);
AA.scale((rect.urx - rect.llx) / (t_urx - t_llx),
(rect.ury - rect.lly) / (t_ury - t_lly));
AA.translate(-t_llx, -t_lly);
// Concatenate the user-specified matrix
AA.concat(matrix);
return AA.unparse();
}
std::string
QPDFAnnotationObjectHelper::getPageContentForAppearance(int rotate)
{
QPDFObjectHandle as = getAppearanceStream("/N");
if (! (as.isStream() && as.getDict().getKey("/BBox").isRectangle()))
{
return "";
}
QPDFObjectHandle::Rectangle rect =
as.getDict().getKey("/BBox").getArrayAsRectangle();
std::string cm = getAnnotationAppearanceMatrix(rotate);
if (cm.empty())
{
return "";
}
std::string as_content = (
"q\n" +
cm + " cm\n" +
QUtil::double_to_string(rect.llx, 5) + " " +
QUtil::double_to_string(rect.lly, 5) + " " +
QUtil::double_to_string(rect.urx - rect.llx, 5) + " " +
QUtil::double_to_string(rect.ury - rect.lly, 5) + " " +
"re W n\n");
PointerHolder<Buffer> buf = as.getStreamData(qpdf_dl_all);
as_content += std::string(
reinterpret_cast<char *>(buf->getBuffer()),
buf->getSize());
as_content += "\nQ\n";
return as_content;
}