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Improve pdf-invert-images example
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@ -1,3 +1,12 @@
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2020-04-07 Jay Berkenbilt <ejb@ql.org>
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* Improve pdf-invert-images example to show a pattern of copying
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streams into another QPDF object to enable a stream data provider
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to access the original stream data.
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* Fix error that caused a compilation error with clang. Fixes
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#424.
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2020-04-06 Jay Berkenbilt <ejb@ql.org>
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* 10.0.0: release
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@ -22,27 +22,77 @@ void usage()
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// Derive a class from StreamDataProvider to provide updated stream
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// data. The main purpose of using this object is to avoid having to
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// allocate memory up front for the objects. A real application might
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// use temporary files in order to avoid having to allocate all the
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// memory. Here, we're not going to worry about that since the goal
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// is really to show how to use this facility rather than to show the
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// best possible way to write an image inverter. This class still
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// illustrates dynamic creation of the new stream data.
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// allocate memory up front for the objects. We want to replace the
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// stream data with a function of the original stream data. In order
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// to do this without actually holding all the images in memory, we
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// create another QPDF object and copy the streams. Copying the
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// streams doesn't actually copy the data. Internally, the qpdf
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// library is holding onto the location of the stream data in the
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// original file, which makes it possible for the StreamDataProvider
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// to access it when it needs it.
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class ImageInverter: public QPDFObjectHandle::StreamDataProvider
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{
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public:
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ImageInverter();
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virtual ~ImageInverter()
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{
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}
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virtual void provideStreamData(int objid, int generation,
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Pipeline* pipeline);
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Pipeline* pipeline) override;
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// Map [og] = image object
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std::map<QPDFObjGen, QPDFObjectHandle> image_objects;
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// Map [og] = image data
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std::map<QPDFObjGen, PointerHolder<Buffer> > image_data;
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void setSelfPh(PointerHolder<QPDFObjectHandle::StreamDataProvider>);
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void registerImage(QPDFObjectHandle image);
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private:
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QPDF other;
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PointerHolder<QPDFObjectHandle::StreamDataProvider> self_ph;
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// Map og in original to copied image
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std::map<QPDFObjGen, QPDFObjectHandle> copied_images;
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};
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ImageInverter::ImageInverter()
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{
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this->other.emptyPDF();
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}
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void
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ImageInverter::setSelfPh(PointerHolder<QPDFObjectHandle::StreamDataProvider> p)
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{
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// replaceStreamData requires a pointer holder to the stream data
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// provider, but there's no way for us to generate one ourselves,
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// so we have to have it handed to us.
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this->self_ph = p;
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}
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void
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ImageInverter::registerImage(QPDFObjectHandle image)
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{
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QPDFObjGen og(image.getObjGen());
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// Store information about the images based on the object and
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// generation number. Recall that a single image object may be
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// used more than once, so no need to update the same stream
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// multiple times.
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if (this->copied_images.count(og) > 0)
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{
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return;
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}
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this->copied_images[og] = this->other.copyForeignObject(image);
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// Register our stream data provider for this stream. Future calls
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// to getStreamData or pipeStreamData will use the new
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// information. Provide null for both filter and decode
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// parameters. Note that this does not mean the image data will be
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// uncompressed when we write the file. By default, QPDFWriter
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// will use /FlateDecode for anything that is uncompressed or
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// filterable in the input QPDF object, so we don't have to deal
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// with it explicitly here. We could explicitly use /DCTDecode and
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// write through a DCT filter if we wanted.
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image.replaceStreamData(this->self_ph,
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QPDFObjectHandle::newNull(),
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QPDFObjectHandle::newNull());
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}
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void
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ImageInverter::provideStreamData(int objid, int generation,
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Pipeline* pipeline)
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@ -50,8 +100,9 @@ ImageInverter::provideStreamData(int objid, int generation,
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// Use the object and generation number supplied to look up the
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// image data. Then invert the image data and write the inverted
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// data to the pipeline.
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QPDFObjGen og(objid, generation);
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PointerHolder<Buffer> data =
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this->image_data[QPDFObjGen(objid, generation)];
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this->copied_images[og].getStreamData(qpdf_dl_all);
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size_t size = data->getSize();
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unsigned char* buf = data->getBuffer();
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unsigned char ch;
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@ -98,6 +149,9 @@ int main(int argc, char* argv[])
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ImageInverter* inv = new ImageInverter;
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PointerHolder<QPDFObjectHandle::StreamDataProvider> p = inv;
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// We need to give ImageInverter the pointer holder that it
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// needs to pass to replaceStreamData.
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inv->setSelfPh(p);
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// For each page...
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std::vector<QPDFPageObjectHelper> pages =
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@ -126,37 +180,13 @@ int main(int argc, char* argv[])
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// whether the image is filterable. Directly inspect
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// keys to determine the image type.
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if (image.pipeStreamData(0, qpdf_ef_compress,
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qpdf_dl_generalized) &&
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qpdf_dl_all) &&
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color_space.isName() &&
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bits_per_component.isInteger() &&
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(color_space.getName() == "/DeviceGray") &&
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(bits_per_component.getIntValue() == 8))
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{
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// Store information about the images based on the
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// object and generation number. Recall that a single
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// image object may be used more than once.
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QPDFObjGen og = image.getObjGen();
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if (inv->image_objects.count(og) == 0)
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{
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inv->image_objects[og] = image;
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inv->image_data[og] = image.getStreamData();
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// Register our stream data provider for this
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// stream. Future calls to getStreamData or
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// pipeStreamData will use the new
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// information. Provide null for both filter
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// and decode parameters. Note that this does
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// not mean the image data will be
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// uncompressed when we write the file. By
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// default, QPDFWriter will use /FlateDecode
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// for anything that is uncompressed or
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// filterable in the input QPDF object, so we
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// don't have to deal with it explicitly here.
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image.replaceStreamData(
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p,
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QPDFObjectHandle::newNull(),
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QPDFObjectHandle::newNull());
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}
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inv->registerImage(image);
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}
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}
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}
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