[mateo-m]

Objective

Let an element draw its subtree into its own texture, then paint that texture over the frame with a blur, a colour matrix, a mask and a blend mode. CSS filter, backdrop-filter, mask-image and mix-blend-mode all need this, and GPUI has no way to do it today.

I need it for GPUIX, a React renderer for GPUI by @remorses. Same change as remorses#7.

I first opened this PR with the whole feature in one diff, then split it so each part gets its own review. This PR is the core: the scene, the style and the window. Stacked on #63793, so the diff GitHub shows includes #63771, #63792 and #63793. This PR alone: mateo-m/zed@zed/gpui-linear-gradients...zed/gpui-effect-layers.

The rest of the stack, in order:

• gpui_apple: render effect layers with Metal #63777 renders the layers with Metal.
• gpui_wgpu: render effect layers with wgpu #63778 renders them with wgpu. This also covers gpui_web, which draws through wgpu.
• gpui_windows: render effect layers with DirectX 11 #63779 renders them with DirectX 11.
• gpui: clip a rounded overflow box through an effect layer #63794 sends a rounded overflow box through a layer, so the clip follows the corner arcs.
• gpui: variable blur for a masked backdrop #63780 replaces the masked backdrop blur with a variable blur.
• gpui: drop-shadow on effect layers #63781 adds drop-shadow.

Until a backend has its PR, its renderer draws a layer's content straight into the frame with no effect. That is why this PR alone changes nothing on screen.

Solution

• LayerEffects in style: blur, color_matrix, backdrop_blur, backdrop_matrix, mask, blend_mode, clips. Each field refines on its own, so a hover style that sets a blur keeps the mask. Styled gets a setter for each, plus background_image and background_blend_mode, which paint through the same layer.
• EffectLayer, ColorMatrix, BlendMode, LayerRegion and BlurPlan in a new effect_layer.rs. The scene gets LayerBegin and LayerEnd batches. EffectLayer is #[repr(C)] so the Metal build can export it through cbindgen.
• Window::paint_effect_layer(bounds, corner_radii, corner_shapes, effects, f). Style::paint calls it when a style has any effect. A content blur grows the layer by three sigmas, the way a CSS filter bleeds past the border box.
• BlurPlan: two Gaussian passes, one per axis, on a texture shrunk by a scale, so a wide blur costs about the same as a narrow one. The renderers read it.
• The three renderers get a no-op arm for the two new batches.
• LayerEffects::clips has no writer until gpui: clip a rounded overflow box through an effect layer #63794. It is part of the struct the three renderers share, so it lands here and the struct layout stays fixed in the later PRs.

Testing

• One new test in crates/gpui/src/style.rs, a_hover_refinement_keeps_the_other_effects. It does not compile against the first version of this PR, where effects refined as one block.
• cargo test -p gpui at this head: 314 passed, 1 doc test passed. cargo check -p gpui -p gpui_wgpu -p gpui_apple --tests passes. cargo fmt --all -- --check is clean.
• cargo check -p gpui_windows --target x86_64-pc-windows-msvc passes from macOS.
• The pixel behaviour is tested in the backend PRs and in GPUIX, not here.
• Performance: an element without effects never opens a layer and takes the old path.
• EffectLayer ends in a pad field, so its size stays a multiple of 8 bytes. The wgpu PR needs that, because WGSL rounds a struct that holds a vec2<f32> up to 8 bytes and the field after the layer in LayerComposite must land at the same offset on both sides.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

---

Release Notes:

• N/A

[cla-bot]

We require contributors to sign our Contributor License Agreement, and we don't have @mateo-m on file. You can sign our CLA at https://zed.dev/cla. Once you've signed, post a comment here that says '@cla-bot check'.

[mateo-m]

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!