refframe-origin-quantize.yaml

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# Regression test for sub-pixel scroll jitter (sticky-in-fractional-reference-frame).

# A scroll frame with a large fractional external scroll offset contains a reference

# frame authored in scrolled space (origin -923.57). The display-list builder

# reconstitutes its origin as origin + external_scroll_offset in f32; at this

# magnitude that round-trip drops a few low bits, yielding 100.49994 instead of the

# intended 100.5 - pure float noise (exact arithmetic gives 100.5). A position:sticky

# frame inside reads that origin through its viewport, so the noise survives into the

# sticky offset (a plain prim would have it cancelled back out by the scroll). With

# the noise the stuck rect's edge sits at device y 30.49994 and snaps to row 30;

# REFERENCE_FRAME_ORIGIN_QUANTUM restores the origin to 100.5 so it snaps to row 31,

# matching the reference (which reconstitutes 100.5 exactly from an integer offset).

root:

  items:

    - type: scroll-frame

      bounds: [0, 0, 200, 400]

      content-size: [200, 4000]

      external-scroll-offset: [0, 1024.07]

      items:

        - type: stacking-context

          bounds: [0, -923.57, 200, 2000]

          transform: translate(0, 0)

          items:

            - type: sticky-frame

              bounds: [0, 100, 200, 20]

              margin-top: 30

              vertical-offset-bounds: [0, 2000]

              items:

                - type: rect

                  bounds: [0, 100, 200, 20]

                  color: green