b903f08e7b
* Share bounded frosted backdrop composition * Scope upload assertions to the backdrop texture * Discard texture updates explicitly in headless rendering tests * Correct texture ID borrowing in upload-count regression * Bound texture sides before queuing backdrop uploads --------- Co-authored-by: Fluorine <joseph.anglada92@gmail.com> Co-authored-by: Joseph Anglada Muñiz <janglada@nd-soft.com>
2.2 KiB
Frosted ribbon and panel backdrops
craft_ui::backdrop extracts the CPU sampling and blur from
WordCraft #4019. It can serve ribbons, rulers,
floating palettes and inspectors without depending on a page renderer or an app's theme.
- Capture the contributing content in the host. Build
Thumbnail::from_imagewhen its pixels change; select a block size appropriate to capture resolution (WordCraft uses about four logical points per cell). - Supply
BackdropLayers in screen coordinates and callcomposefor the covered area. Layers without captures use their fallback color, so first-frame rendering remains defined. - Keep a
BackdropTextureper region/context and upload the composed image. Paint its full UV rectangle behind controls using normal egui clipping and apply a caller-chosen tint.
The output uses bilinear thumbnail samples and three separable box-blur passes (five cells sideways/two vertically), intended for soft UI glass, not photographic filtering. Capture pixels are premultiplied; they composite over the supplied paper's opaque RGB. Output is opaque and the host's overlaid tint supplies translucency. No brightness threshold or dark/light alpha is hard-coded. Choose tint for text contrast and provide an opaque fallback when transparency is off.
Inputs are validated before multiplication/allocation. Source images are capped at 16,777,216
pixels, thumbnails/output at 262,144 texels, output and uploaded texture sides at 1024. A long,
thin upload is rejected even when its total pixel count fits; the existing cache is preserved.
Invalid captures/areas return
None; invalid layer rectangles are ignored. Identical texture images skip uploads. Distinct
windows/contexts use distinct cache instances; dropping one releases its texture.
The host owns capture and invalidation, including changes while transparency is off. When the effect is re-enabled, backfill missing/stale captures before using them. Keep captures out of the composition being captured to avoid feedback. Consumer adoption and GPU framebuffer capture are separate work; this module adds no renderer callback, global UI flag or document dependency.