A knockout group that is not isolated, and whose elements blend, is
drawn over a copy of the art below it when the renderer has no layer
open around it. Each element was drawn over the whole copy in a layer,
and the layer was cut to the element's knockout shape with DestIn.
Where the shape covers part of a pixel, the cut counted the element's
coverage a second time. With Page Knockout Group on and Page Isolated
Blending off, the page is drawn this way as soon as an object on it
outside an isolated group has a blend mode other than Normal, on itself
or on a fill or stroke. On a test page, adding a Multiply square
changed the half-covered edge of a blue square over orange from
[115, 115, 141] to [172, 159, 147] on white.
Each element is now drawn over the copy offscreen, over its own
bounds. With the DestOut pass before it, each pixel gets (1 - shape)
times what was below plus shape times the element composited with the
copy at a shape of 1, as ISO 32000-1 section 11.4.6 describes. Pixels
that the shape covers fully or not at all are drawn as before.
A transparency group whose members blend with the art below it, and a
masked object with a blend mode, are drawn over a copy of that art. For
each such group in each frame, the renderer rendered everything drawn
so far into a new pixmap the size of its context (on the canvas, the
whole view), started that context again and drew that pixmap back into
it as an image, which the next copy and the frame rendered again. At
2880x1800, a document with 50 translucent groups, each holding a
Multiply rectangle, took 299 ms a frame on 8 threads.
Every render that composites in 8 bits, the canvas included, now keeps
that picture and renders what the context draws next over it. The
backdrop is still cut from the picture. The 50 groups take 65 ms a
frame, and the frames have the same pixels. Renders that composite in
floating point (raster exports, Save for Web, Object › Rasterize and
Crop Image) still draw the picture back.
Docs: docs/target-app-parity.md.
The renderer composited in 8-bit integers, so where a partly transparent
anti-aliased edge crossed opaque art (or a background colour) the result
came out at alpha 254 on some pixels, and PNG, TIFF and WebP files were
written with an alpha channel. Raster exports (and Save for Web) now
composite in floating point (vello_cpu's f32 pipeline, enabled as a
feature), offscreen groups, masks and patterns included; the canvas keeps
the faster 8-bit path.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
PNG is written by an in-code chunk writer with the resolution in pHYs and optional Adam7
interlacing (JPEG stores the resolution in JFIF). document.export takes ppi (72/150/300/other,
wins over scale), background (transparent, white, black or a colour) and antiAlias (none, art,
type: text snapped to whole pixels); Export for Screens rows take them too (plus one top-level
antiAlias, and a row's ppi names its @Nx suffix), and so does object.rasterize. Hard edges stay
hard in every offscreen pass (groups, masks, filters), whatever the thread count.
RenderOptions.anti_alias and render::encode::RasterExportOptions; PNG/JPEG/WebP Options dialog
(pngOptions/jpgOptions/webpOptions) after File > Export As PNG.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
On screen, a group (or object) with opacity, a blend mode, an opacity mask or
knockout whose content blends is drawn offscreen over a copy of its backdrop
and mixed back in by its opacity, mask and clip (a group blend mode then
applies to the backdrop-free result, as PDF defines it). Isolate Blending keeps
the content starting from transparency. Clip groups no longer isolate their
children (blending content is clipped per drawing), and non-isolated knockout
groups composite their elements against the art below the group. Groups
without blending inside still render as plain layers.
In PDF, such groups are written as non-isolated transparency groups (a
constant-alpha soft mask instead of the writer's isolated opacity group),
knockout groups included.
doc: Node::blends_through / children_blend.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
