feat: add non-destructive adjustment layers

core/adjustment-layer.ts

@@ -0,0 +1,26 @@
+import type { BaseLayer } from "./base-layer";
+
+export type ColorAdjustment = {
+  brightness: number;
+  contrast: number;
+  saturation: number;
+  colorBalance: { red: number; green: number; blue: number };
+};
+
+/**
+ * A non-destructive adjustment affecting pixels already composited beneath it
+ * on its artboard. Adjustment layers are top-level artboard nodes so live WebGL
+ * and exported PNG compositing have identical scope. Transform and masks are
+ * intentionally unsupported.
+ */
+export type AdjustmentLayer = BaseLayer & {
+  type: "adjustment";
+  adjustment: ColorAdjustment;
+};
+
+export const neutralColorAdjustment: ColorAdjustment = {
+  brightness: 0,
+  contrast: 0,
+  saturation: 0,
+  colorBalance: { red: 0, green: 0, blue: 0 },
+};

core/index.ts

@@ -15,6 +15,8 @@ export type {
 } from "./geometry";
 export type { ArtboardId, AssetId, DocumentId, GenerationCandidateId, GenerationJobId, LayerId } from "./id";
 export type { ImageLayer } from "./image-layer";
+export type { AdjustmentLayer, ColorAdjustment } from "./adjustment-layer";
+export { neutralColorAdjustment } from "./adjustment-layer";
 export type { Layer } from "./layer";
 export type { LayerMask } from "./layer-mask";
 export { getLayerMask, hasLayerMask } from "./layer-mask-utils";

core/layer.ts

@@ -1,5 +1,6 @@
 import type { ImageLayer } from "./image-layer";
 import type { LayerGroup } from "./layer-group";
 import type { RasterLayer } from "./raster-layer";
+import type { AdjustmentLayer } from "./adjustment-layer";
 
-export type Layer = ImageLayer | RasterLayer | LayerGroup;
+export type Layer = ImageLayer | RasterLayer | LayerGroup | AdjustmentLayer;