Transparent property

Esta entrada API conserva identificadores, firmas, bloques de código y términos PDF en su forma original.

Whether the currently active page contains transparent content.

Transparent returns True when the active page contains any object whose effective alpha is less than 1.0 or which references a graphics state that enables transparency — soft masks, opacity values (CA / ca), non-default blend modes (/BM), or transparency groups (PDF 1.7 spec section 11). It is the same flag PDFium checks internally to decide whether the page must be rendered through its transparent-page rasterizer.

The property is False when Active is False or when the page is purely opaque. Pages that are transparent are slightly more expensive to render — PDFium has to allocate an alpha channel and composite each object against the page background — so detecting transparency up front lets callers pick the right output target (32-bit ARGB TBitmap, PDF watermark overlay, printer’s alpha-aware path).

The value is a per-page property; iterate every page if you need a document-wide “has transparency anywhere?” answer. Combine with the Background color when rendering to a flat bitmap: a transparent page on a clWhite background produces flattened output, whereas rendering on a transparent surface preserves alpha for downstream compositing.

• Highlight annotations, watermarks and stamp overlays commonly trigger transparency on otherwise opaque pages.
• Use this flag to short-circuit alpha-channel handling: opaque pages can be rendered to a 24-bpp bitmap and saved as JPEG without information loss.
• Detecting transparency is O(1) — PDFium stores the flag during content stream parsing, so reading the property is essentially free.

Active, PageNumber, ObjectTransparent, RenderPage