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Add languages parameter to hOCR output metadata #4531

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Add languages parameter to hOCR output metadata #4531

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cebd193
Add languages parameter to hOCR output metadata
mvanhorn Mar 20, 2026
fbec60b
fix: use ISO 639-1 codes and separate script models in hOCR metadata
mvanhorn Mar 24, 2026
43706b8
fix: handle compound model names and address review feedback
mvanhorn Mar 25, 2026
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3 changes: 3 additions & 0 deletions include/tesseract/renderer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -173,13 +173,16 @@ class TESS_API TessHOcrRenderer : public TessResultRenderer {
explicit TessHOcrRenderer(const char *outputbase, bool font_info);
explicit TessHOcrRenderer(const char *outputbase);

void SetInputLanguages(const char *languages);

protected:
bool BeginDocumentHandler() override;
bool AddImageHandler(TessBaseAPI *api) override;
bool EndDocumentHandler() override;

private:
bool font_info_; // whether to print font information
std::string input_languages_;
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Copilot AI Mar 24, 2026

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Adding std::string input_languages_ to TessHOcrRenderer changes the size/layout of this exported (TESS_API) C++ class, which can break binary compatibility for downstream code that links against libtesseract and instantiates TessHOcrRenderer. If ABI stability is a concern, consider storing the new state behind an indirection (pimpl/opaque pointer) or in a separate internal structure to minimize ABI impact.

Suggested change
std::string input_languages_;
// NOTE: Additional per-instance state (e.g. input languages) is stored
// out-of-line to avoid changing the ABI-visible layout of this class.

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};

/**
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13 changes: 12 additions & 1 deletion src/api/hocrrenderer.cpp
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Expand Up @@ -477,6 +477,12 @@ TessHOcrRenderer::TessHOcrRenderer(const char *outputbase, bool font_info)
font_info_ = font_info;
}

void TessHOcrRenderer::SetInputLanguages(const char *languages) {
if (languages) {
input_languages_ = languages;
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Copilot AI Mar 24, 2026

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SetInputLanguages(nullptr) currently leaves any previously set value intact, which can produce stale ocr-langs metadata if a renderer instance is reused and the caller tries to clear the languages. Consider explicitly clearing input_languages_ when languages == nullptr (or provide a ClearInputLanguages()), so the behavior is unambiguous.

Suggested change
if (languages) {
input_languages_ = languages;
if (languages && languages[0] != '\0') {
input_languages_ = languages;
} else {
input_languages_.clear();

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}
}

bool TessHOcrRenderer::BeginDocumentHandler() {
AppendString(
"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
Expand All @@ -496,8 +502,13 @@ bool TessHOcrRenderer::BeginDocumentHandler() {
if (font_info_) {
AppendString(" ocrp_font ocrp_fsize");
}
AppendString("'/>\n");
if (!input_languages_.empty()) {
AppendString(" <meta name='ocr-langs' content='");
AppendString(input_languages_.c_str());
AppendString("' />\n");
}
AppendString(
"'/>\n"
" </head>\n"
" <body>\n");

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1 change: 1 addition & 0 deletions src/tesseract.cpp
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Expand Up @@ -516,6 +516,7 @@ static void PreloadRenderers(tesseract::TessBaseAPI &api,
bool font_info;
api.GetBoolVariable("hocr_font_info", &font_info);
auto renderer = std::make_unique<tesseract::TessHOcrRenderer>(outputbase, font_info);
renderer->SetInputLanguages(api.GetInitLanguagesAsString());
if (renderer->happy()) {
renderers.push_back(std::move(renderer));
} else {
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