Filters and adjustment layers

Filters are WGSL compute kernels. The same kernel serves two purposes: applying a filter to a layer's pixels, and adjustment layers that filter non-destructively. Both paths therefore produce identical pixels.

Gaussian blur is built in.

Applying a filter

const blur = { type: 'gaussian-blur', radius: 8 } as const;
 
await doc.setFilterPreview({ nodeId, filter: blur }); // shown live, not in history
await doc.dispatch(ops.applyFilter({ nodeId, filter: blur }));
await doc.setFilterPreview(null);

applyFilter runs on the GPU and reads the result back into tiles. Pixels outside the issuer's selection never change; along soft selection edges the kernel blends its result with the original by coverage. If the kernel fails on the GPU, the batch is skipped and onError receives the reason, so a broken filter never commits pixels. It is an asynchronous operation; the document applies operations one at a time, so ordering is kept.

Adjustment layers

const adjustment = ops.addAdjustmentLayer({ parentId: folderId, filter: blur });
await doc.dispatch(adjustment);
await doc.dispatch(ops.updateNode({ nodeId: adjustment.nodeId, props: { filter: { type: 'gaussian-blur', radius: 2 } } }));

An adjustment layer filters the composite of everything below it in the same folder, including sub-folders, and blends the result back with its own opacity and blend mode. The effect never leaks out of the folder. A folder containing adjustment layers is composited in isolation even when it is set to pass-through, which differs from Krita.

Determinism

Kernels use integer arithmetic only. Integer operations are exact, while floating-point precision and rounding vary between GPUs, so the results are bit-identical everywhere. Each collaborator can therefore recompute apply-filter locally and the operation never has to carry pixels. The blur quantizes its weights to sum to 1 << 16 and accumulates in u32; it works on premultiplied pixels so transparent areas do not bleed color.

Your own filters

Filters are registered at runtime creation, so an application can add kernels of its own. See Custom filters.