Review of #4898 (CodeRabbit): a shading clearing in another blend-mode
pass cleared its whole drawing path, so a small mesh triangle erased the
earlier elements of its pass around it. The same happened in the
shading's own pass, and in any knockout group, because a knockout paint
is copied over the path and a mesh texture is transparent outside its
triangles.
A shading in a knockout group now goes through knockout_shading: the
shading at full opacity, composited with Compose::DestOut, clears its
own shape (mesh triangles, /BBox), then in its own pass it is painted
with SrcOver. A shading that paints nothing still clears nothing. The
clear uses the shading without the fill opacity it carries, so a
half-transparent shading still replaces all of what is under it.
Test: it::knockout_backdrop::a_small_mesh_replaces_only_what_is_under_its_triangle
(own pass, another pass, isolated group). Revert-proven per half; keeping
the opacity in the clear fails
raster::tests::knockout_groups_replace_what_their_elements_cover.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SqmHYx8FiWM5PcsoiErgp9
Review of #4898 (FredApps):
- An image or nested group of another blend mode than the pass's composited
its layer at opacity 0, on the assumption that its shape was cleared first.
`knockout_image` skips images with an `/SMask` and stencil masks, so a
white Difference square stayed under a blue Normal masked image in the
Difference pass and turned it yellow. The layer now composites with
`Compose::DestOut` at full opacity and no soft mask, clearing exactly its
coverage.
- In another pass (and an erase pass), a shading cleared under its path
before the mesh-extent check that makes an off-page mesh paint nothing,
so a Difference `sh` of such a mesh erased the blue under it. The clear
now makes the same decision (`shading_bbox`, `mesh_area`, shared with the
paint path).
Tests: `it::knockout_backdrop` gains a masked image, a stencil and an
off-page mesh case; each fails with its half of the fix reverted.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SqmHYx8FiWM5PcsoiErgp9
A non-isolated knockout group starts from the backdrop under it (ISO 32000-2
§11.4.7, §11.4.8), but was drawn into a layer of its own starting transparent,
so a blend mode inside it had nothing to blend with: white with /BM /Difference
over magenta stayed white (#4886).
Entered plainly (full opacity, no soft mask, Normal, not itself a knockout
element), the group is now drawn once per blend mode its elements use. Each pass
is a knockout layer composited onto the backdrop in that mode; elements of other
modes clear what is under their shape instead of painting. The Normal pass finds
the other modes, so a group without blend modes takes one pass as before.
hayro-interpret patch 67 (Device::begin_knockout_pass / end_knockout_pass,
draw_knockout_passes), hayro patch 26 (the renderer side). Test:
pdfcraft-render it::knockout_backdrop, three cases failing with the fix
reverted, plus an isolated-group control.
Fixes#4886
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SqmHYx8FiWM5PcsoiErgp9
