LlosLab Software Development BlogEngineering notes for PDF, Delphi, and document software developers.

기술 문서

PDFium Component: Delphi에서 render cache and zoom performance

PDFium Component

Delphi와 C++Builder 애플리케이션에는 PDFium VCL Component 워크플로를, Lazarus/FPC에는 PDFium LCL Component 워크플로를 통합하여 보기, 렌더링, 폼, 인쇄, 프리플라이트 보고서, 표준 중심 검증을 소스 코드 컴포넌트로 구현할 수 있습니다.

이 글은 developers building document viewers that must feel responsive on large PDFs and high-DPI displays을 위한 글입니다. render cache and zoom performance을 단순한 컴포넌트 호출이 아니라 운영 환경의 문서 엔지니어링으로 다룹니다.

실제 위험은 zooming can appear fast in a sample but stutter under large pages, thumbnails, annotations, continuous scrolling, or memory pressure입니다. 따라서 명확한 계약, 관찰 가능한 진단, 실제 고객 파일을 반영한 회귀 샘플이 필요합니다.

아키텍처 결정

Define cache policy as viewer behavior. cache key fields such as page, zoom, rotation, DPI, color mode, and annotation state / memory budget, eviction strategy, thumbnail sharing, and prefetch distance

  • cache key fields such as page, zoom, rotation, DPI, color mode, and annotation state
  • memory budget, eviction strategy, thumbnail sharing, and prefetch distance
  • progressive rendering behavior for fast preview versus final-quality output
  • cancellation rules when users scroll, resize, search, or change zoom quickly

구현 흐름

Measure the interaction path, not only render time. The order below keeps the workflow reviewable for Delphi and C++Builder teams.

  1. record render requests through one queue instead of direct control event handlers
  2. reuse cached bitmaps only when the key fully matches the visible state
  3. render low-latency placeholders before high-quality pages when appropriate
  4. cancel stale jobs and evict pages outside the viewport and prefetch window
  5. measure frame latency and memory during realistic scroll and zoom sequences

검증 증거

Performance evidence users can feel. Keep these fields with the output or support record.

  • cache hit rate, render latency, queue depth, cancellation count, and memory peak
  • viewport size, zoom level, DPI, page dimensions, and color-filter state
  • time to first preview and time to final-quality render
  • eviction and prefetch behavior during continuous scrolling

Caching is a user-experience feature

A render cache should balance page quality, memory budget, cancellation, invalidation, and perceived latency. The viewer needs to cancel stale work when the user scrolls or zooms rather than finishing irrelevant renders.

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.

  • cache key fields such as page, zoom, rotation, DPI, color mode, and annotation state
  • memory budget, eviction strategy, thumbnail sharing, and prefetch distance
  • progressive rendering behavior for fast preview versus final-quality output
  • cancellation rules when users scroll, resize, search, or change zoom quickly
  • cache hit rate, render latency, queue depth, cancellation count, and memory peak
  • viewport size, zoom level, DPI, page dimensions, and color-filter state

render cache and zoom performance에 대한 엔지니어링 검토 노트

이 검토 노트를 사용해 기능이 데모 단계를 넘어섰고 출시, 지원, 고객 에스컬레이션 상황에서 설명할 수 있는지 확인합니다

  • 결정: cache key fields such as page, zoom, rotation, DPI, color mode, and annotation state. 구현상 핵심 지점: reuse cached bitmaps only when the key fully matches the visible state. 승인 증거: time to first preview and time to final-quality render. 회귀 트리거: rendering thumbnails and pages through separate caches wastes memory
  • 결정: memory budget, eviction strategy, thumbnail sharing, and prefetch distance. 구현상 핵심 지점: render low-latency placeholders before high-quality pages when appropriate. 승인 증거: eviction and prefetch behavior during continuous scrolling. 회귀 트리거: large engineering drawings can exceed cache assumptions made for letters or invoices
  • 결정: progressive rendering behavior for fast preview versus final-quality output. 구현상 핵심 지점: cancel stale jobs and evict pages outside the viewport and prefetch window. 승인 증거: cache hit rate, render latency, queue depth, cancellation count, and memory peak. 회귀 트리거: annotation overlays invalidate cached pages when review state changes
  • 결정: cancellation rules when users scroll, resize, search, or change zoom quickly. 구현상 핵심 지점: measure frame latency and memory during realistic scroll and zoom sequences. 승인 증거: viewport size, zoom level, DPI, page dimensions, and color-filter state. 회귀 트리거: high-DPI displays multiply bitmap memory even when page count is small
  • 결정: cache key fields such as page, zoom, rotation, DPI, color mode, and annotation state. 구현상 핵심 지점: record render requests through one queue instead of direct control event handlers. 승인 증거: time to first preview and time to final-quality render. 회귀 트리거: rendering thumbnails and pages through separate caches wastes memory
  • 결정: memory budget, eviction strategy, thumbnail sharing, and prefetch distance. 구현상 핵심 지점: reuse cached bitmaps only when the key fully matches the visible state. 승인 증거: eviction and prefetch behavior during continuous scrolling. 회귀 트리거: large engineering drawings can exceed cache assumptions made for letters or invoices
  • 결정: progressive rendering behavior for fast preview versus final-quality output. 구현상 핵심 지점: render low-latency placeholders before high-quality pages when appropriate. 승인 증거: cache hit rate, render latency, queue depth, cancellation count, and memory peak. 회귀 트리거: annotation overlays invalidate cached pages when review state changes

경계 사례

  • large engineering drawings can exceed cache assumptions made for letters or invoices
  • annotation overlays invalidate cached pages when review state changes
  • high-DPI displays multiply bitmap memory even when page count is small
  • rendering thumbnails and pages through separate caches wastes memory

Delphi / C++Builder 참고 사항

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. 중요한 용어는 render cache, zoom, DPI, progressive rendering, eviction, prefetch.

Delphi 코드 예제

다음 Delphi 스케치는 이 주제에 맞는 실무형 서비스 경계를 보여 줍니다. 정책 검사, 로깅, 검증을 좁은 제품 호출 구간 밖에 두면 워크플로를 테스트하기 쉽습니다.

procedure TPreviewForm.RenderCachedPage(PageIndex: Integer; Zoom: Double);
var
  CacheKey: string;
begin
  CacheKey := Format('%d:%.2f', [PageIndex, Zoom]);
  if not FRenderCache.TryGetValue(CacheKey, FPageBitmap) then
  begin
    FPageBitmap := PdfView.RenderPage(PageIndex, 0, Round(850 * Zoom), Round(1100 * Zoom), ro0, []);
    FRenderCache.Add(CacheKey, FPageBitmap);
  end;
  PaintBitmap(FPageBitmap);
end;

운영 체크리스트

  • 워크플로는 빈 파일, 일반 고객 파일, 최악의 파일에서 실행합니다
  • 생성된 PDF는 대상 뷰어, 검증기, 프린터 또는 downstream 애플리케이션에서 엽니다
  • 제품 버전, 프로필 버전, 입력 해시, 출력 경로, 경과 시간, 경고 수를 기록합니다
  • 암호, 인증서, 임시 파일, 고객 데이터는 명확한 보존 규칙에 따라 관리합니다
  • 고객 파일이 새로운 경계 사례를 드러내면 회귀 문서를 추가합니다

제품 문서

PDFium Component

추가 코드 예제

procedure TViewerForm.RequestRender(TargetZoom: Single);
var
  Status: TPdfProgressiveStatus;
begin
  if FTokenSource <> nil then
    FTokenSource.Cancel;           // abandon the previous in-flight render
  FTokenSource := TPdfCancellationTokenSource.New;  // FPdfAsync unit

  Status := Pdf.RenderPageProgressive(FBackBuffer, 0, 0,
    FBackBuffer.Width, FBackBuffer.Height, FTokenSource.Token,
    ro0, [reAnnotations]);

  case Status of
    prsDone:      PresentBackBuffer;
    prsCancelled: ;                // superseded by a newer request: drop silently
    prsFailed:    ShowRenderFailure;
  end;
end;