svgfe-backdrop-ext-scroll-offset.yaml

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# Tests that an SVGFE *backdrop* filter subregion is normalized by the external

# scroll offset exactly like the item geometry it applies to, so that subregion

# and geometry live in one space. The backdrop filter's picture composites in

# backdrop-root space rather than the scrolling node's, but that is a difference

# of spatial node, which frame building maps through the spatial tree

# (SurfaceInfo::svgfe_source_map) - it is not a reason to author the two in

# different spaces. The green flood subregion is therefore authored at the same

# y as the backdrop-filter item (50), not pre-offset by the 50px external scroll

# offset; both are normalized identically and the flood exactly covers the red

# backdrop. Originally written for bug 2046779, which compensated for the

# mismatch by skipping normalization; bug 1975275 showed that cannot be made

# correct - a scaling reference frame between the element and the backdrop root

# (e.g. pdf.js scaling its text spans) needs a full mapping, not a translation.

root:

  items:

    - type: scroll-frame

      bounds: [0, 0, 100, 100]

      content-size: [100, 1000]

      scroll-offset: [0, 0]

      external-scroll-offset: [0, 50]

      items:

        - type: rect

          color: red

          bounds: [0, 50, 100, 100]

        - type: backdrop-filter

          bounds: [0, 50, 100, 100]

          filters:

            - svgfe: SourceGraphic

            - svgfe: flood

              linear: false

              color: green

              subregion: [0, 50, 100, 100]

            - svgfe: compositeover

              linear: false

              subregion: [0, 0, 100, 1000]

              in: 1

              in2: 0