image-studio/view/canvas/brush.ts

import { commandIds } from "@commands/ids";
import type { ImageDocument } from "@core/document";
import type { Vec2D } from "@core/geometry";
import type { Layer } from "@core/layer";
import type { RasterLayer } from "@core/raster-layer";
import type { EditorState } from "@editor/state";
import { isPanInteractionMode } from "@editor/tools";
import type { AppStore } from "@editor/store";

export type BrushSession = {
  layerId: string;
  assetId: string;
  previousPoint: Vec2D;
  mode: "brush" | "eraser";
  source?: string;
  pending?: Promise<void>;
  cancelled?: boolean;
};

export function beginBrushSession(document: ImageDocument, editor: EditorState, point: Vec2D): BrushSession | undefined {
  const layer = resolveBrushTargetLayer(document, editor);
  if (!layer || (editor.tools.activeTool !== "brush" && editor.tools.activeTool !== "eraser")) return undefined;
  return { layerId: layer.id, assetId: layer.assetId, previousPoint: point, mode: editor.tools.activeTool };
}

export function canPreviewBrush(document: ImageDocument, editor: EditorState): boolean {
  return Boolean(resolveBrushTargetLayer(document, editor));
}

export function brushUnavailableHint(document: ImageDocument, editor: EditorState): string | undefined {
  if (isPanInteractionMode(editor.tools.interactionMode) || (editor.tools.activeTool !== "brush" && editor.tools.activeTool !== "eraser")) return undefined;
  if (resolveBrushTargetLayer(document, editor)) return undefined;

  const layerId = editor.maskEdit?.maskLayerId ?? editor.selection.layerIds[0];
  if (!layerId) {
    if (editor.selection.artboardId) return "Brushes paint layers, not artboards. Select or add a raster layer first.";
    return "Select a raster layer or layer mask to paint.";
  }

  const layer = findLayer(document.artboards.flatMap((artboard) => artboard.layers), layerId);
  if (!layer) return "Select a raster layer or layer mask to paint.";
  if (layer.locked) return "Unlock this layer before painting.";
  if (layer.type === "image") return "Image layers are non-destructive. Add a layer mask to paint or erase.";
  if (layer.type === "group") return "Select a raster layer inside the group to paint.";
  if (!editor.maskEdit && !layer.visible) return "Show this layer before painting.";
  return "Select a raster layer or layer mask to paint.";
}

function resolveBrushTargetLayer(document: ImageDocument, editor: EditorState): RasterLayer | undefined {
  if (isPanInteractionMode(editor.tools.interactionMode) || (editor.tools.activeTool !== "brush" && editor.tools.activeTool !== "eraser")) return undefined;
  const editingMask = Boolean(editor.maskEdit);
  const layerId = editor.maskEdit?.maskLayerId ?? editor.selection.layerIds[0];
  if (!layerId) return undefined;
  const layer = findRasterLayer(document.artboards.flatMap((artboard) => artboard.layers), layerId);
  if (!layer || layer.locked || (!editingMask && !layer.visible)) return undefined;
  return layer;
}

export function updateBrushSession(options: {
  store: AppStore;
  session: BrushSession;
  point: Vec2D;
  color: string;
  size: number;
  hardness: number;
}): BrushSession {
  const state = options.store.getState();
  const layer = findRasterLayer(state.document.artboards.flatMap((artboard) => artboard.layers), options.session.layerId);
  if (!layer) return options.session;

  const asset = state.document.assets.find((candidate) => candidate.id === layer.assetId);
  if (!asset) return options.session;

  const from = options.session.previousPoint;
  const to = options.point;
  options.session.previousPoint = to;
  options.session.pending = (options.session.pending ?? Promise.resolve())
    .then(async () => {
      if (options.session.cancelled) return;

      const source = await drawStroke({
        source: options.session.source ?? asset.source,
        width: asset.intrinsicSize.w,
        height: asset.intrinsicSize.h,
        from: documentPointToAssetPoint(from, layer, asset.intrinsicSize.w, asset.intrinsicSize.h),
        to: documentPointToAssetPoint(to, layer, asset.intrinsicSize.w, asset.intrinsicSize.h),
        color: state.editor.maskEdit ? "#ffffff" : options.color,
        size: options.size,
        hardness: options.hardness,
        mode: options.session.mode,
      });

      if (options.session.cancelled) return;
      options.session.source = source;
      options.store.dispatch(commandIds.toolSetBrushStrokePreview, { layerId: options.session.layerId, assetId: options.session.assetId, source });
    })
    .catch(() => undefined);

  return options.session;
}

export async function commitBrushSession(options: { store: AppStore; session: BrushSession }) {
  await options.session.pending;
  if (options.session.cancelled) return;

  if (options.session.source) options.store.dispatch(commandIds.documentUpdateAssetSource, { assetId: options.session.assetId, source: options.session.source });
  options.store.dispatch(commandIds.toolSetBrushStrokePreview, undefined);
}

export function cancelBrushSession(options: { store: AppStore; session: BrushSession }) {
  options.session.cancelled = true;
  options.store.dispatch(commandIds.toolSetBrushStrokePreview, undefined);
}

function documentPointToAssetPoint(point: Vec2D, layer: RasterLayer, width: number, height: number): Vec2D {
  return {
    x: ((point.x - layer.transform.position.x) / Math.max(0.0001, layer.transform.scale.x) / width) * width,
    y: ((point.y - layer.transform.position.y) / Math.max(0.0001, layer.transform.scale.y) / height) * height,
  };
}

async function drawStroke(options: {
  source: string;
  width: number;
  height: number;
  from: Vec2D;
  to: Vec2D;
  color: string;
  size: number;
  hardness: number;
  mode: "brush" | "eraser";
}) {
  const canvas = document.createElement("canvas");
  canvas.width = Math.max(1, Math.round(options.width));
  canvas.height = Math.max(1, Math.round(options.height));
  const context = canvas.getContext("2d");
  if (!context) return options.source;

  const image = await loadImage(options.source);
  context.drawImage(image, 0, 0, canvas.width, canvas.height);
  const hardness = Math.max(0, Math.min(100, options.hardness)) / 100;
  context.globalCompositeOperation = options.mode === "eraser" ? "destination-out" : "source-over";
  context.strokeStyle = options.color;
  context.shadowColor = options.mode === "eraser" ? "rgba(0,0,0,1)" : options.color;
  context.shadowBlur = (1 - hardness) * options.size;
  context.lineWidth = options.size;
  context.lineCap = "round";
  context.lineJoin = "round";
  context.beginPath();
  context.moveTo(options.from.x, options.from.y);
  context.lineTo(options.to.x, options.to.y);
  context.stroke();
  context.globalCompositeOperation = "source-over";

  return canvas.toDataURL("image/png");
}

function loadImage(source: string) {
  return new Promise<HTMLImageElement>((resolve, reject) => {
    const image = new Image();
    image.onload = () => resolve(image);
    image.onerror = () => reject(new Error("Failed to load raster layer"));
    image.src = source;
  });
}

function findRasterLayer(layers: Layer[], layerId: string): RasterLayer | undefined {
  const layer = findLayer(layers, layerId);
  return layer?.type === "raster" ? layer : undefined;
}

function findLayer(layers: Layer[], layerId: string): Layer | undefined {
  for (const layer of layers) {
    if (layer.id === layerId) return layer;
    if (layer.type === "group") {
      const child = findLayer(layer.children, layerId);
      if (child) return child;
    }
  }
  return undefined;
}