feat(api): render a DocumentSession directly to images#227
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Getting a raster from a document meant calling toPdfBytes() and then reloading those bytes with Loader.loadPDF to hand a PDDocument to PDFRenderer — a serialize-then-reparse round-trip. Add DocumentSession.toImages(int dpi) and toImage(int pageIndex, int dpi), plus transparent ARGB overloads, returning java.awt.image.BufferedImage and rasterizing the in-memory document directly. The PDF backend's document build is extracted into buildDocument(...), shared by the existing save path and a new renderToImages(...); the PDFRenderer/ImageType calls stay in the backend, so the public surface stays PDFBox-free (BufferedImage is JDK). PdfVisualRegression gains direct renderPages(session) / assertMatchesBaseline(name, session) overloads, and EmojiSvgVsPngExample rasterises through toImage instead of the round-trip.
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Why
Getting a raster image from a document meant calling
toPdfBytes()and then reloading those bytes withLoader.loadPDFto hand aPDDocumentto PDFBox'sPDFRenderer— a serialize-then-reparse round-trip (and a second full document in memory). PDFBox can rasterize aPDDocumentdirectly, so previews, thumbnails, and pixel diffs need no PDF byte detour.What
DocumentSession.toImages(int dpi)→List<BufferedImage>(one per page) andtoImage(int pageIndex, int dpi)→BufferedImage, plustransparentoverloads returning ARGB instead of opaque white. The return type is the JDKjava.awt.image.BufferedImage, so the public surface stays PDFBox-free.buildDocument(...), shared by the existing save path and a newrenderToImages(...); thePDFRenderer/ImageTypecalls stay inbackend.fixed.pdf.PdfVisualRegressiongains directrenderPages(session)/assertMatchesBaseline(name, session)overloads;EmojiSvgVsPngExamplerasterises throughtoImage(0, 96, true)instead of the round-trip.dpi <= 0, an out-of-range page index, and an empty document are rejected; rendering failures surface asDocumentRenderingException.Tests
./mvnw test -pl .green (1494 tests). NewDocumentSessionImageTest(10): one image per page sized to the page at the DPI; dimensions scale with DPI; rendered pages contain painted pixels;transparentyields an ARGB image with a fully-transparent margin while the default is opaque RGB;toImagereturns the requested page and is pixel-identical to the matchingtoImagesentry; a watermark lands in the raster; and the direct render is pixel-identical to thetoPdfBytes()round-trip (ImageDiff, budget 0). Examples compile andEmojiSvgVsPngExampleregenerates.