feat: implement inpainting functionality with mask handling

- Added `createMaskedPixelReplacementSource` function to handle pixel replacement using inpainting.
- Introduced `buildInpaintBundle` to prepare inpainting data including mask generation and validation.
- Created utility functions for mask operations such as `applyMaskedContentModeToRgba`, `expandRectWithinBounds`, and others for mask manipulation.
- Developed tests for inpainting preparation and mask raster utilities to ensure functionality and correctness.
- Implemented mask raster operations including inversion, feathering, blurring, and more.

view/generate/candidateActions.ts

@@ -0,0 +1,50 @@
+import type { ImageDocument } from "@core/document";
+import type { GenerationCandidate } from "@editor/state";
+import { loadImageCanvas, maskValueFromRgba } from "../mask/maskRaster";
+
+export async function createMaskedPixelReplacementSource(document: ImageDocument, candidate: GenerationCandidate): Promise<string> {
+  if (!candidate.inpaint) throw new Error("Only inpaint candidates can replace masked pixels.");
+
+  const targetAsset = document.assets.find((asset) => asset.id === candidate.inpaint?.sourceAssetId);
+  if (!targetAsset) throw new Error("The source layer for this candidate no longer exists.");
+
+  const targetCanvas = await loadImageCanvas(targetAsset.source, targetAsset.intrinsicSize.w, targetAsset.intrinsicSize.h);
+  const generatedCanvas = await loadImageCanvas(candidate.source, candidate.width, candidate.height);
+  const maskCanvas = await loadImageCanvas(candidate.inpaint.maskImage, candidate.width, candidate.height);
+
+  const targetContext = require2dContext(targetCanvas);
+  const generatedContext = require2dContext(generatedCanvas);
+  const maskContext = require2dContext(maskCanvas);
+  const targetData = targetContext.getImageData(0, 0, targetCanvas.width, targetCanvas.height);
+  const generatedData = generatedContext.getImageData(0, 0, generatedCanvas.width, generatedCanvas.height);
+  const maskData = maskContext.getImageData(0, 0, maskCanvas.width, maskCanvas.height);
+  const crop = candidate.inpaint.crop.assetBounds;
+
+  for (let y = 0; y < candidate.height; y += 1) {
+    for (let x = 0; x < candidate.width; x += 1) {
+      const targetX = Math.round(crop.x) + x;
+      const targetY = Math.round(crop.y) + y;
+      if (targetX < 0 || targetY < 0 || targetX >= targetCanvas.width || targetY >= targetCanvas.height) continue;
+
+      const generatedIndex = (y * generatedCanvas.width + x) * 4;
+      const targetIndex = (targetY * targetCanvas.width + targetX) * 4;
+      const mask = maskValueFromRgba(maskData.data, generatedIndex) / 255;
+      if (mask <= 0) continue;
+
+      for (let channel = 0; channel < 4; channel += 1) {
+        const previous = targetData.data[targetIndex + channel] ?? 0;
+        const next = generatedData.data[generatedIndex + channel] ?? previous;
+        targetData.data[targetIndex + channel] = Math.round(previous * (1 - mask) + next * mask);
+      }
+    }
+  }
+
+  targetContext.putImageData(targetData, 0, 0);
+  return targetCanvas.toDataURL("image/png");
+}
+
+function require2dContext(canvas: HTMLCanvasElement): CanvasRenderingContext2D {
+  const context = canvas.getContext("2d");
+  if (!context) throw new Error("Unable to prepare generated candidate");
+  return context;
+}