Render: raster effects are made again when patterns, symbols, images, settings or fonts change

The renderer kept the rasters of an object's drop shadows, outer glows
and filtered content (Gaussian Blur, Feather and the Photoshop-style
filters), and drew them again while the object, the zoom and rotation
and the ink plane stayed the same. The content drawn into a raster also
reads things outside the object: patterns, symbols, brushes, images,
document, layer and color settings, the knockout a group inherits, the
fonts, and the options the frame is drawn with. When one of them
changed, a renderer that had drawn the object went on drawing the
raster it had kept, made from the old values.

Each kept raster now records what its content was drawn from: which of
those things the object reads, found by walking the object when the
raster is made, and a hash of their values then. The renderer draws
the raster only while that hash is the same in the current frame. Once
a frame, the renderer hashes the document's patterns, symbols and
images. It hashes their art and pixels by the addresses of their
shared values, and it keeps weak references to those values while a
raster made with them is kept, so no other value can take one of those
addresses. A filtered raster also records the color channels its
filters split, and under De-Interlace the raster resolution.

A temporary release test timed the inputs of 400 kept rasters at about
10 microseconds a frame.

docs/target-app-parity.md

@@ -515,6 +515,8 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 
 - **Moving objects with raster effects (#1257):** during a drag or a dialog's preview, an object whose content only moved draws its cached drop shadows, outer glows and filtered content (Gaussian Blur, Feather and the Photoshop-style filters) from the rasters of an earlier frame at the nearest whole pixel, without running the effects again. The renderer first draws the moved content where the old content lies in its raster and compares the pixels. De-Interlace runs again. The frame after the drag runs the effects again and draws what a fresh renderer draws; on the desktop, the canvas renders that frame on the render worker. `texture_drag_perf` times a drag's frames and the frame after it.
 
+- **Raster effects after document and view changes:** a cached drop shadow, outer glow or filtered content is made again when something its content reads from outside the object changes: a pattern's art or tiling, a symbol shown inside another symbol, a brush definition, an image's pixels, the raster resolution (De-Interlace), Page Knockout Group, Document Setup's substitution highlights, a layer's Dim Images, the color settings, the fonts, Pixel Preview, Anti-aliased Artwork, Overprint Preview and isolation mode. A thumbnail under Color Halftone or Mezzotint is made again when the document's color mode changes.
+
 - **Full font names (#1258):** OpenType name ID 4 identifies its face alongside family/legacy/PostScript names, including localized names, for loaded fonts, cataloged files and Missing Fonts searches. Synthetic name-table regressions cover full names distinct from their PostScript name, real-family precedence and variable fonts' default faces. Windows font-service activation remains unverified; scores and hours are unchanged.
 ## Revision history