fix(core-presentation): render PDF transparency-group soft-mask images - #25718
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…gbluebutton#23953) Port of the v3.0.x fix to v4.0.x-develop. Certain PDFs embed a figure inside a transparency group (/Group /S /Transparency) as an image with a soft mask (/SMask) and an ICCBased colorspace. poppler's cairo backend fails to composite this construct: pdftocairo -svg emits a nested mask+filter alpha-to-luminance construct that browsers evaluate to fully transparent, and pdftocairo -png rasterizes it blank as well, so the slide uploads "successfully" but renders blank. The splash backend (pdftoppm) composites it correctly. Two-part fix in bbb-common-web: - Trigger the raster fallback when the generated SVG contains a cairo transparency-group soft mask, gated on the <filter> count (not <mask>): cairo emits a <filter> only for the blanking construct, while plain alpha images emit <mask> with zero <filter> and render fine as vectors. - Rasterize with pdftoppm (splash) instead of pdftocairo -png so the fallback actually produces the figure. 4.0 adaptations relative to the 3.0 change: - Coexists with the maskTagThreshold machinery from bigbluebutton#25513: the analysis grep counts <image|<path|<use|<mask|<filter, the rasterize condition keeps both gates, and doc-conversion.xml wires filterTagThreshold with the same safe-default syntax (:0) as maskTagThreshold. - SvgConversionHandlerTest extended to cover numberOfFilterTags() through the same analysis-pipeline replication used for mask tags. Playwright: uploads blurImage.pdf (the reproduction from the issue) and asserts the rendered slide is not blank by rasterizing the served slide SVG and measuring the near-black pixel ratio, for both moderator and attendee.
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Repository UI Review profile: CHILL Plan: Team Run ID: 📒 Files selected for processing (3)
Included review availability: Your plan provides up to 8 included reviews per hour; 7 remain after this review. WalkthroughThe SVG conversion handler counts Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🔵 Low · up to Affected PDF slides now use pdftoppm for raster fallback and filter-containing SVGs rasterize by default, improving correctness for soft-masked images. The change is localized and mergeable with owner awareness that deployed environments must provide the renderer while preserving existing conversion timeout and isolation controls. Sequence Diagram(s)sequenceDiagram
participant PresentationTest
participant SvgImageCreatorImp
participant SvgConversionHandler
participant pdftoppm
PresentationTest->>SvgImageCreatorImp: Upload blurred-image PDF
SvgImageCreatorImp->>SvgConversionHandler: Count SVG filter tags
SvgConversionHandler-->>SvgImageCreatorImp: Return filter-tag count
SvgImageCreatorImp->>pdftoppm: Rasterize page when threshold is reached
pdftoppm-->>SvgImageCreatorImp: Produce PNG slide image
SvgImageCreatorImp-->>PresentationTest: Render slide
PresentationTest->>PresentationTest: Measure dark-pixel ratio
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✅ Passed checks (3 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 28.57% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 14 functions across 6 files. (2 skipped: 2 unsupported.)
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In `@bigbluebutton-tests/playwright/presentation/presentation.ts`:
- Line 580: Update uploadSinglePresentation to capture the attendee slide’s HTML
before uploading, then poll until the attendee slide HTML changes before calling
getCurrentSlideDarkPixelRatio(this.userPage); retain the existing
moderator-slide wait and use the established slide-selection/polling helpers.
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Configuration used: Repository UI
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⛔ Files ignored due to path filters (1)
bigbluebutton-tests/playwright/core/media/blurImage.pdfis excluded by!**/*.pdf
📒 Files selected for processing (9)
bbb-common-web/src/main/java/org/bigbluebutton/presentation/handlers/SvgConversionHandler.javabbb-common-web/src/main/java/org/bigbluebutton/presentation/imp/SvgImageCreatorImp.javabbb-common-web/src/test/scala/org/bigbluebutton/presentation/handlers/SvgConversionHandlerTest.scalabigbluebutton-tests/playwright/core/elements.tsbigbluebutton-tests/playwright/presentation/presentation.spec.tsbigbluebutton-tests/playwright/presentation/presentation.tsbigbluebutton-tests/playwright/presentation/util.tsbigbluebutton-web/grails-app/conf/bigbluebutton.propertiesbigbluebutton-web/grails-app/conf/spring/doc-conversion.xml
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…uring uploadSinglePresentation only waits on the moderator page, so the attendee-side dark-pixel assertion could measure the previous slide and pass on its content. Snapshot the attendee slide before the upload and poll until it changes (review finding on bigbluebutton#25718).
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…uring uploadSinglePresentation only waits on the moderator page, so the attendee-side dark-pixel assertion could measure the previous slide and pass on its content. Snapshot the attendee slide before the upload and poll until it changes. Mirrors the review finding on the 4.0 port (bigbluebutton#25718).
paultrudel
reviewed
Sep 1, 2026
Review feedback on PR bigbluebutton#25718: most BBB settings use 0 to mean the check is turned off, and the sibling maskTagThreshold already follows that pattern. Previously filterTagThreshold=0 meant 'rasterize any slide with a <filter> tag' and the gate compared with count > threshold, so there was no clean way to disable the check (short of setting an absurdly large value). Now 0 skips the filter check entirely and N triggers rasterization at count >= N, mirroring the maskTagThreshold gate. The default moves from 0 to 1 so effective behavior is unchanged: any slide whose generated SVG contains a <filter> tag is still rasterized by default, keeping the issue 23953 safeguard on out of the box.
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paultrudel
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Sep 1, 2026
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What does this PR do?
Fixes the silent blanking of PDF slides that embed a soft-masked image inside a transparency group, by porting the v3.0.x fix (antobinary#17) to
v4.0.x-develop:<filter>tags in the generated SVG.pdftocairoemits a<filter>(alpha-to-luminance) only when a PDF transparency group is used as a soft mask (/SMask) — the exact construct browsers render blank. Plain alpha images emit only<mask>(zero<filter>) and are unaffected, so they stay vector.filterTagThresholdsetting (default0= any<filter>rasterizes the slide).pdftoppm(poppler's splash backend) instead ofpdftocairo -png— the cairo backend renders the same construct blank even as a PNG, so without this the fallback would produce a blank bitmap too.blurImage.pdf(the reproduction from the issue) and asserts the served slide is not blank by rasterizing the slide SVG and measuring its near-black pixel ratio, for both moderator and attendee.Before / after, converting the reproduction PDF from #23953 (the "before" output is measurably pure white — mean 65535/65535):
Closes Issue(s)
Closes #23953
Motivation
A user uploads a perfectly valid PDF, the conversion reports success, and the slide comes out completely blank — with no error anywhere to point at the cause. The root cause is poppler's cairo backend failing to composite a transparency group combining a soft mask with an ICCBased colorspace; both of BBB's conversion paths (
pdftocairo -svgand thepdftocairo -pngfallback) go through that backend, so the failure was unrecoverable. The splash backend (pdftoppm) and Ghostscript both render the same file correctly.How to test
bigbluebutton-tests/playwright/core/media/blurImage.pdfto a meeting — the slide must show the black blurred-edge rectangle, not a blank page. No special setup needed: the<filter>gate is active by default (filterTagThreshold=0).uploadTest.png) — it must still convert to vector SVG (no needless rasterization; gating on<mask>instead of<filter>would break this, which is why the gate is on<filter>).presentation.spec.ts→ "Upload PDF with embedded soft-masked image renders (not blank)".More
maskTagThresholdmachinery from fix(bbb-web): Fallback to Rasterization if SVG has (lots of) Mask Tags #25513 — the analysis grep counts<image|<path|<use|<mask|<filter, the rasterize condition keeps both gates, anddoc-conversion.xmlwiresfilterTagThresholdwith the same safe-default syntax (:0).SvgConversionHandlerTestis extended to covernumberOfFilterTags().v4.0.x-developwith pre-existingnot found: value iterrors in several specs — unrelated to this PR, worth a separate fix.filterTagThresholddocumented inbigbluebutton.properties, in plain language: what 0 does, what raising it means, why >100 makes no sense)