valerybokov opened a new pull request, #491: URL: https://github.com/apache/pdfbox/pull/491
PDFBOX-6077: Fix stencil masks filled with a pattern Summary A PDF image used as a stencil mask (an ImageMask) can be filled with a pattern instead of a solid color. PDFBox renders this case specially: it draws the pattern's paint and the mask into two separate scratch images, then combines them pixel-by-pixel before compositing the result onto the page. Two independent bugs in that combine step caused patterns used this way to render incorrectly. Bug 1 — mask alpha overwrote the paint's own alpha The combine step did: rasterPixel[3] = alphaPixel[0]; unconditionally replacing the paint's alpha with the mask's alpha. Any pixel the pattern itself never painted into — for example the gaps between tiles of a tiling pattern — has alpha 0 in the paint image, but that got overwritten with the mask's (opaque) alpha, turning transparent gaps into solid black. Fix: combine the two alphas by multiplication instead of overwriting: rasterPixel[3] = rasterPixel[3] * alphaPixel[0] / 255; so a pixel is only visible where both the pattern painted something and the mask allows it through. Bug 2 — soft-masked patterns rendered fully transparent A pattern can itself have a soft mask applied to it (SoftMask, wrapping the pattern's own Paint). SoftMask looks up its backing (grayscale) raster using absolute page-device pixel coordinates, fixed at the point the soft mask's transparency group was rendered. Because the stencil-mask-with-pattern code fills into an isolated scratch image — not the real page Graphics2D — those coordinates no longer lined up with anything, and the soft mask silently applied zero alpha everywhere, making the pattern disappear entirely. Fix: unwrap the soft mask, fill the scratch image with its plain underlying paint, then apply the soft mask's own alpha afterward via a new PageDrawer.applySoftMaskAlpha(), which looks up the mask's backing raster directly using a per-pixel device-coordinate transform — correct regardless of the scratch image's resolution — rather than relying on the Paint/PaintContext machinery that assumes it's rendering onto the real page raster. SoftMask gains a few narrow package-private accessors for this. Commits 1. PDFBOX-6077: combine stencil mask alpha with the pattern's own alpha 2. PDFBOX-6077: fix soft-masked patterns used as a stencil mask fill --------------- Per https://www.apache.org/legal/generative-tooling.html: portions of this PR were produced with assistance from Claude Code (Anthropic), based on a bug was described in Apache PDFBOX Issue Tracker. I've reviewed the generated code and confirm to the best of my knowledge that the output does not include any third-party copyrighted material and is compatible with the Apache License 2.0. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
