ObjectBounds 属性

The PDF content stream of a page is a sequence of page objects: text runs, vector paths, raster images, shading patterns, and embedded form XObjects (PDF 32000-1 § 8.2). ObjectBounds returns the bounding box of object number Index on the current page after PDFium has flattened the CTM stack and the object's own cm matrix, so the rectangle is directly usable for hit testing, mask building, or thumbnail crops without any further math.

The rectangle uses the standard PDF coordinate convention — origin at the lower-left corner of the page, units of 1/72 inch, Y growing upward — so Bottom < Top in a well-formed document. Wraps PDFium's FPDFPageObj_GetBounds; the call is O(1) on its own but iterates every contour vertex internally for paths, so caching the result is wise if you read it many times per object.

Valid range is 0 .. ObjectCount - 1 for the page currently selected by PageNumber. Accessing an out-of-range index returns a zero rectangle. Pair this property with ObjectType to dispatch on the kind of object before reading additional per-type properties.

• The box is the geometric bounding rectangle; ink coverage may be narrower because of clipping paths or shading masks.
• Text objects report the union of every glyph box plus the rise/descent of the active font, not the visual cap-height rectangle.
• For image and form XObjects the rectangle equals the parallelogram corners after the object's CTM is applied, snapped to an axis-aligned bounding box.
• If the page has been rotated via PageRotation the bounds are still reported in the unrotated PDF coordinate space.