wasm wrapper: add function to reader to scan multiple barcode #567
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wrappers/wasm/BarcodeReader.cpp
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| std::vector<ReadResult> results{}; | ||
| std::string error{}; | ||
| }; | ||
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I like the approach used here more. I mean to simply return a vector<ReadResult> instead of a new composite data type ReadResults. If there should be an exception, then adding a 1-element vector with the error message set, is a viable solution.
wrappers/wasm/BarcodeReader.cpp
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| ReadResults readResults{}; | ||
| readResults.results.reserve(results.size()); | ||
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| for ( auto& result : results) { |
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If not too much of a hassle, please use clang-format to format your edits.
wrappers/wasm/BarcodeReader.cpp
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| @@ -57,13 +68,49 @@ ReadResult readBarcodeFromImage(int bufferPtr, int bufferLength, bool tryHarder, | |||
| if (buffer == nullptr) | |||
| return {"", "", "Error loading image"}; | |||
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| return readBarcodeFromImageView({buffer.get(), width, height, ImageFormat::Lum}, tryHarder, format); | |||
| ReadResults results = readBarcodesFromImageView({buffer.get(), width, height, ImageFormat::Lum}, tryHarder, format, 1); | |||
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I think it would be better to implement readBardcodeFromImage by calling readBardcodesFromImage and thereby not duplicating the stbi_load_... calls?
wrappers/wasm/demo_reader.html
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| ctx.stroke(); | ||
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| // Example to use JavaScript Array created from an Iterator | ||
| const resultArray = Array.from(new ReaderResultVectorIterator(results)); |
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Creating an array with a copy of the data here, only to then iterate over it in an indexed for loop, does not make much sense to me. Please either use the .size(), .get() API or the for( ... on ...) syntax.
wrappers/wasm/demo_reader.html
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| @@ -12,6 +12,46 @@ | |||
| zxing = instance; // this line is supposedly not required but with current emsdk it is :-/ | |||
| }); | |||
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| /* | |||
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This iterator seems a bit over the top, just to replace a for( int ... ) with a for( ... on ... ) loop in this simple demo, but I generally like abstractions and maybe someone learns something from it for a 'real' application. Keep it or leave it, as you prefer.
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Thanks for the review. I've just added commits to:
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wrappers/wasm/BarcodeReader.cpp
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| { | ||
| using namespace ZXing; | ||
| auto results = readBarcodesFromImage(bufferPtr, bufferLength, tryHarder, format, 1); | ||
| return results.front(); |
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This will fail/throw/segfault if results is empty. A line like return results.empty() ? ReadResult() : results.front(); should work.
wrappers/wasm/BarcodeReader.cpp
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| } | ||
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| ReadResult readBarcodeFromPixmap(int bufferPtr, int imgWidth, int imgHeight, bool tryHarder, std::string format) | ||
| { | ||
| using namespace ZXing; | ||
| return readBarcodeFromImageView({reinterpret_cast<uint8_t*>(bufferPtr), imgWidth, imgHeight, ImageFormat::RGBX}, tryHarder, format); | ||
| auto results = readBarcodesFromPixmap(bufferPtr, imgWidth, imgHeight, tryHarder, format, 1); | ||
| return results.front(); |
Thanks for the review, I've just fixed it. I've just tested manually with the old and new demo_reader page and images available in the test/samples/multi-1 folder :) |
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Thanks a lot. I decided to squash the 6 commits into 1. |
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It looks like immediately after I merged this, someone discovered an issue with the new code: #568. Could you maybe have a look at it? |
I wrote a new patch as discussed in #565 to update the wasm wrapper to allow to scan multiple barcodes with only one call.
This patch adds two new functions
readBarcodesFromPixmapandreadBarcodesFromPixmap. They return a new structureReadResults. All found barcode are stored in thevector<ReadResult> resultsproperty (theirerrorproperty is always empty). If an error occurs theresultsvector is empty and thestd::string errorproperty ofReadResultsis filled with the exception message.This patch is compatible with the two functions
readBarcodeFromPixmapandreadBarcodeFromPixmapwhich returned only oneReadResultwith error inside it directly.In #565 we discussed to add a default value for
maxSymbols: I did not add it because it wasn't usable from the JavaScript side (an error was raised by the browser saying I had to give 5 arguments and only 4 were found).About the JavaScript way to use the result: the
register_vectoremscripten function is creating a new interface and some JavaScript boilerplate code should be added to use the result.See the binding.h emscripten file to view all methods available to interact with a vector: https://github.com/emscripten-core/emscripten/blob/98b618f09bc106d401c0045fa7252f1cd15bd3c0/system/include/emscripten/bind.h#L1894
User can either create C-like for loops with the
.size()and.get(int i)methods or create a JavaScript Iterator to wrap the received result.I've updated the demo_reader to show how to create and use the Iterator way.
The Iterator can be used with two different style: either directly loop on it (see
showScanResults) or use it to create a native Javascript Array (seeshowImageWithResults).If you prefer to not show this Iterator way, I can update the demo_reader to use only C-style for loops.
The demo_reader has been improved to show result in an ordered list in text and to add the result index on each barcode found in the image.