diff options
Diffstat (limited to 'examples/pdf-filter-tokens.cc')
| -rw-r--r-- | examples/pdf-filter-tokens.cc | 74 |
1 files changed, 30 insertions, 44 deletions
diff --git a/examples/pdf-filter-tokens.cc b/examples/pdf-filter-tokens.cc index 68d6e149..4a06bcd2 100644 --- a/examples/pdf-filter-tokens.cc +++ b/examples/pdf-filter-tokens.cc @@ -1,7 +1,6 @@ // -// This example illustrates the use of QPDFObjectHandle::TokenFilter -// with addContentTokenFilter. Please see comments inline for details. -// See also pdf-count-strings.cc for a use of +// This example illustrates the use of QPDFObjectHandle::TokenFilter with addContentTokenFilter. +// Please see comments inline for details. See also pdf-count-strings.cc for a use of // QPDFObjectHandle::TokenFilter with filterContents. // @@ -26,9 +25,8 @@ usage() exit(2); } -// The StringReverser class is a trivial example of using a token -// filter. This class only overrides the pure virtual handleToken -// function and preserves the default handleEOF function. +// The StringReverser class is a trivial example of using a token filter. This class only overrides +// the pure virtual handleToken function and preserves the default handleEOF function. class StringReverser: public QPDFObjectHandle::TokenFilter { public: @@ -39,15 +37,12 @@ class StringReverser: public QPDFObjectHandle::TokenFilter void StringReverser::handleToken(QPDFTokenizer::Token const& token) { - // For string tokens, reverse the characters. For other tokens, - // just pass them through. Notice that we construct a new string - // token and write that, thus allowing the library to handle any - // subtleties about properly encoding unprintable characters. This - // function doesn't handle multibyte characters at all. It's not - // intended to be an example of the correct way to reverse - // strings. It's just intended to give a simple example of a - // pretty minimal filter and to show an example of writing a - // constructed token. + // For string tokens, reverse the characters. For other tokens, just pass them through. Notice + // that we construct a new string token and write that, thus allowing the library to handle any + // subtleties about properly encoding unprintable characters. This function doesn't handle + // multibyte characters at all. It's not intended to be an example of the correct way to reverse + // strings. It's just intended to give a simple example of a pretty minimal filter and to show + // an example of writing a constructed token. if (token.getType() == QPDFTokenizer::tt_string) { std::string value = token.getValue(); std::reverse(value.begin(), value.end()); @@ -57,9 +52,8 @@ StringReverser::handleToken(QPDFTokenizer::Token const& token) } } -// The ColorToGray filter finds all "rg" operators in the content -// stream and replaces them with "g" operators, thus mapping color to -// grayscale. Note that it only applies to content streams, not +// The ColorToGray filter finds all "rg" operators in the content stream and replaces them with "g" +// operators, thus mapping color to grayscale. Note that it only applies to content streams, not // images, so this will not replace color images with grayscale // images. class ColorToGray: public QPDFObjectHandle::TokenFilter @@ -99,29 +93,23 @@ ColorToGray::numericValue(QPDFTokenizer::Token const& token) void ColorToGray::handleToken(QPDFTokenizer::Token const& token) { - // Track the number of non-ignorable tokens we've seen. If we see - // an "rg" following three numbers, convert it to a grayscale - // value. Keep writing tokens to the output as we can. - - // There are several things to notice here. We keep two stacks: - // one of "meaningful" tokens, and one of all tokens. This way we - // can preserve whitespace or comments that we encounter in the - // stream and there preserve layout. As we receive tokens, we keep - // the last four meaningful tokens. If we see three numbers - // followed by rg, we use the three numbers to calculate a gray - // value that is perceptually similar to the color value and then - // write the "g" operator to the output, discarding any spaces or - // comments encountered embedded in the "rg" operator. - - // The stack and all_stack members are updated in such a way that - // they always contain exactly the same non-ignorable tokens. The - // stack member contains the tokens that would be left if you + // Track the number of non-ignorable tokens we've seen. If we see an "rg" following three + // numbers, convert it to a grayscale value. Keep writing tokens to the output as we can. + + // There are several things to notice here. We keep two stacks: one of "meaningful" tokens, and + // one of all tokens. This way we can preserve whitespace or comments that we encounter in the + // stream and there preserve layout. As we receive tokens, we keep the last four meaningful + // tokens. If we see three numbers followed by rg, we use the three numbers to calculate a gray + // value that is perceptually similar to the color value and then write the "g" operator to the + // output, discarding any spaces or comments encountered embedded in the "rg" operator. + + // The stack and all_stack members are updated in such a way that they always contain exactly + // the same non-ignorable tokens. The stack member contains the tokens that would be left if you // removed all space and comment tokens from all_stack. - // On each new token, flush out any space or comment tokens. Store - // the incoming token. If we just got an rg preceded by the right - // kinds of operands, replace the command. Flush any additional - // accumulated tokens to keep the stack only four tokens deep. + // On each new token, flush out any space or comment tokens. Store the incoming token. If we + // just got an rg preceded by the right kinds of operands, replace the command. Flush any + // additional accumulated tokens to keep the stack only four tokens deep. while ((!this->all_stack.empty()) && isIgnorable(this->all_stack.at(0).getType())) { writeToken(this->all_stack.at(0)); @@ -182,11 +170,9 @@ main(int argc, char* argv[]) QPDF pdf; pdf.processFile(infilename); for (auto& page: QPDFPageDocumentHelper(pdf).getAllPages()) { - // Attach two token filters to each page of this file. - // When the file is written, or when the pages' contents - // are retrieved in any other way, the filters will be - // applied. See comments on the filters for additional - // details. + // Attach two token filters to each page of this file. When the file is written, or when + // the pages' contents are retrieved in any other way, the filters will be applied. See + // comments on the filters for additional details. page.addContentTokenFilter( std::shared_ptr<QPDFObjectHandle::TokenFilter>(new StringReverser)); page.addContentTokenFilter( |