Delphi/C++Builder には PDFium VCL Component のワークフローを、Lazarus/FPC には PDFium LCL Component のワークフローを組み込み、表示、レンダリング、フォーム、印刷、プリフライトレポート、標準対応の検証をソースコード付きコンポーネントで実装できます。
この記事は Delphi teams building PDF viewers for public-sector, education, healthcare, or internal operations users 向けです。accessible PDF reader design を単なるコンポーネント呼び出しではなく、本番向けのドキュメントエンジニアリングとして扱います。
実務上のリスクは accessibility cannot be added by a toolbar at the end if focus order, text extraction, color modes, keyboard navigation, and document diagnostics are not part of the viewer architecture です。そのため、明確な契約、観測可能な診断、実際の顧客ファイルに近い回帰サンプルが必要です。
アーキテクチャ上の判断
Design the reader around user tasks, not only pages. keyboard model for page navigation, search, selection, panels, and annotations / focus order between the document viewport, thumbnails, form fields, and side panels
- keyboard model for page navigation, search, selection, panels, and annotations
- focus order between the document viewport, thumbnails, form fields, and side panels
- fallback behavior when a document lacks tags, text, or usable reading order
- color, zoom, contrast, and speech-assistance modes that do not alter the source file
実装フロー
Combine rendering with semantic inspection. The order below keeps the workflow reviewable for Delphi and C++Builder teams.
- define reader tasks and keyboard shortcuts before wiring viewer controls
- extract text and document structure where available and expose diagnostics
- connect focus updates to page, selection, form field, and annotation events
- test zoom, contrast, search, and speech cues on tagged and untagged files
- record unsupported document conditions as user-facing warnings
検証エビデンス
Accessibility evidence to keep with releases. Keep these fields with the output or support record.
- keyboard path coverage, focus transitions, text extraction status, and search behavior
- PDF/UA or structure diagnostics when available
- screen-reader notes for supported controls and viewer panels
- low-vision mode settings used during verification
Accessible viewing starts with predictable navigation
An accessible PDF reader has to expose document state, keyboard paths, focus changes, text selection, search results, zoom behavior, and low-vision display choices consistently. Rendering accuracy is necessary but not sufficient.
Profile ownership and versioning
A named, versioned profile is easier to review than options scattered across forms, scripts, and batch parameters. It also makes support reports readable when customers use older templates or policies.
- keyboard model for page navigation, search, selection, panels, and annotations
- focus order between the document viewport, thumbnails, form fields, and side panels
- fallback behavior when a document lacks tags, text, or usable reading order
- color, zoom, contrast, and speech-assistance modes that do not alter the source file
- keyboard path coverage, focus transitions, text extraction status, and search behavior
- PDF/UA or structure diagnostics when available
Engineering review notes for accessible PDF reader design
Use these review notes to make sure the feature has moved beyond a demo and can be defended during release, support, and customer escalation.
- Decision: keyboard model for page navigation, search, selection, panels, and annotations. Implementation pressure point: extract text and document structure where available and expose diagnostics. Acceptance evidence: screen-reader notes for supported controls and viewer panels. Regression trigger: contrast filters should be reversible and should not modify the PDF itself
- Decision: focus order between the document viewport, thumbnails, form fields, and side panels. Implementation pressure point: connect focus updates to page, selection, form field, and annotation events. Acceptance evidence: low-vision mode settings used during verification. Regression trigger: image-only PDFs need OCR or a clear warning rather than silent empty text
- Decision: fallback behavior when a document lacks tags, text, or usable reading order. Implementation pressure point: test zoom, contrast, search, and speech cues on tagged and untagged files. Acceptance evidence: keyboard path coverage, focus transitions, text extraction status, and search behavior. Regression trigger: rotated pages and mixed page sizes can break hit-testing and focus cues
- Decision: color, zoom, contrast, and speech-assistance modes that do not alter the source file. Implementation pressure point: record unsupported document conditions as user-facing warnings. Acceptance evidence: PDF/UA or structure diagnostics when available. Regression trigger: thumbnail panes should not trap keyboard users away from the document
- Decision: keyboard model for page navigation, search, selection, panels, and annotations. Implementation pressure point: define reader tasks and keyboard shortcuts before wiring viewer controls. Acceptance evidence: screen-reader notes for supported controls and viewer panels. Regression trigger: contrast filters should be reversible and should not modify the PDF itself
- Decision: focus order between the document viewport, thumbnails, form fields, and side panels. Implementation pressure point: extract text and document structure where available and expose diagnostics. Acceptance evidence: low-vision mode settings used during verification. Regression trigger: image-only PDFs need OCR or a clear warning rather than silent empty text
境界ケース
- image-only PDFs need OCR or a clear warning rather than silent empty text
- rotated pages and mixed page sizes can break hit-testing and focus cues
- thumbnail panes should not trap keyboard users away from the document
- contrast filters should be reversible and should not modify the PDF itself
Delphi / C++Builder notes
PDFium Component should sit behind a small service boundary that receives files, streams, profiles, and credentials, then returns output paths, warnings, metrics, and validation status. Important terms include TPdfView, keyboard navigation, PDF/UA, reading order, focus, low-vision mode.
Delphi コード例
次の Delphi スケッチは、このテーマに対する実用的なサービス境界を示します。ポリシー確認、ログ記録、検証を製品呼び出しの狭い部分の外側に置くと、ワークフローをテストしやすくなります。
procedure TReaderForm.LoadReadingStream(const FileName: string; PageNo: Integer);
begin
PdfView.LoadFromFile(FileName);
if (PageNo < 1) or (PageNo > PdfView.PageCount) then
raise ERangeError.Create('Page number is outside the document');
FReadingUnits := ExtractTaggedReadingOrder(PdfView, PageNo);
QueueSpeech(FReadingUnits);
RenderPagePreview(PageNo);
end;本番チェックリスト
- Run the workflow on an empty file, a normal customer file, and a worst-case file
- Open the generated PDF with the target viewer, validator, printer, or downstream application
- Log product version, profile version, input hash, output path, elapsed time, and warning count
- Keep passwords, certificates, temporary files, and customer data under explicit retention rules
- Add regression documents when a customer file exposes a new edge case