fix: limit scale patch composite to edit regions

app/api/canvas/local-edit/route.ts

@@ -3900,6 +3900,7 @@ export async function POST(request: NextRequest) {
             featherMaxPx: 42,
             featherMinPx: 10,
             featherRatio: 0.018,
+            regions: scaleAdjustCompositeRegions,
             sourceImageUrl,
             workspaceRegion: scaleAdjustPatchReference.workspaceRect,
           }

lib/canvas/generate-image.ts

@@ -56,6 +56,7 @@ export interface CanvasLocalEditCompositeConfig {
 export interface CanvasScaleAdjustPatchCompositeConfig {
   sourceImageUrl: string;
   workspaceRegion: CanvasLocalEditCompositeRegion;
+  regions?: CanvasLocalEditCompositeRegion[];
   featherMinPx?: number;
   featherMaxPx?: number;
   featherRatio?: number;
@@ -384,10 +385,18 @@ function normalizeScaleAdjustPatchCompositeConfig(
   if (!/^https?:\/\//i.test(sourceImageUrl)) return null;
   const workspaceRegion = normalizeCanvasRegion(value.workspaceRegion);
   if (!workspaceRegion) return null;
+  const regions = Array.isArray(value.regions)
+    ? value.regions
+        .map((region) => normalizeCanvasRegion(region))
+        .filter((region): region is CanvasLocalEditCompositeRegion =>
+          Boolean(region)
+        )
+    : [];
 
   return {
     sourceImageUrl,
     workspaceRegion,
+    ...(regions.length > 0 ? { regions } : {}),
     featherMaxPx: normalizeOptionalNumber(value.featherMaxPx, {
       max: 180,
       min: 0,
@@ -2335,6 +2344,7 @@ function buildScaleAdjustPatchCompositeMaskSvg(params: {
   width: number;
   height: number;
   featherPx: number;
+  regions?: Array<{ left: number; top: number; width: number; height: number }>;
   touchesLeft: boolean;
   touchesTop: boolean;
   touchesRight: boolean;
@@ -2342,6 +2352,46 @@ function buildScaleAdjustPatchCompositeMaskSvg(params: {
 }) {
   const { height, width } = params;
   const featherPx = Math.max(0, Math.round(params.featherPx));
+  const regions = params.regions?.filter(
+    (region) => region.width > 0 && region.height > 0
+  );
+  if (regions?.length) {
+    const blur = Math.max(1, featherPx);
+    const softPad = Math.max(2, Math.round(featherPx * 1.35));
+    const corePad = Math.max(0, Math.round(featherPx * 0.22));
+    const softRects = regions
+      .map((region) => {
+        const left = Math.max(0, region.left - softPad);
+        const top = Math.max(0, region.top - softPad);
+        const right = Math.min(width, region.left + region.width + softPad);
+        const bottom = Math.min(height, region.top + region.height + softPad);
+        return `<rect x="${left}" y="${top}" width="${Math.max(1, right - left)}" height="${Math.max(1, bottom - top)}" fill="#ffffff" filter="url(#scale-adjust-patch-soft-mask)" />`;
+      })
+      .join("");
+    const coreRects = regions
+      .map((region) => {
+        const left = Math.max(0, region.left - corePad);
+        const top = Math.max(0, region.top - corePad);
+        const right = Math.min(width, region.left + region.width + corePad);
+        const bottom = Math.min(height, region.top + region.height + corePad);
+        return `<rect x="${left}" y="${top}" width="${Math.max(1, right - left)}" height="${Math.max(1, bottom - top)}" fill="#ffffff" />`;
+      })
+      .join("");
+
+    return Buffer.from(`
+      <svg width="${width}" height="${height}" viewBox="0 0 ${width} ${height}" xmlns="http://www.w3.org/2000/svg">
+        <defs>
+          <filter id="scale-adjust-patch-soft-mask" x="-50%" y="-50%" width="200%" height="200%" color-interpolation-filters="sRGB">
+            <feGaussianBlur stdDeviation="${blur}" />
+          </filter>
+        </defs>
+        <rect x="0" y="0" width="${width}" height="${height}" fill="rgba(0,0,0,0)" />
+        ${softRects}
+        ${coreRects}
+      </svg>
+    `);
+  }
+
   if (featherPx <= 0) {
     return Buffer.from(`
       <svg width="${width}" height="${height}" viewBox="0 0 ${width} ${height}" xmlns="http://www.w3.org/2000/svg">
@@ -2671,9 +2721,37 @@ async function applyScaleAdjustPatchCompositeToImages(params: {
   const touchesTop = workspaceBox.top <= 0;
   const touchesRight = workspaceBox.left + workspaceBox.width >= sourceWidth;
   const touchesBottom = workspaceBox.top + workspaceBox.height >= sourceHeight;
+  const maskRegionBoxes = composite.regions
+    ?.map((region) =>
+      rectToPixelBox({
+        height: sourceHeight,
+        region,
+        width: sourceWidth,
+      })
+    )
+    .map((box) => {
+      const left = Math.max(0, box.left - workspaceBox.left);
+      const top = Math.max(0, box.top - workspaceBox.top);
+      const right = Math.min(
+        workspaceBox.width,
+        box.left + box.width - workspaceBox.left
+      );
+      const bottom = Math.min(
+        workspaceBox.height,
+        box.top + box.height - workspaceBox.top
+      );
+      return {
+        left,
+        top,
+        width: Math.max(0, right - left),
+        height: Math.max(0, bottom - top),
+      };
+    })
+    .filter((box) => box.width > 0 && box.height > 0);
   const patchMask = buildScaleAdjustPatchCompositeMaskSvg({
     featherPx,
     height: workspaceBox.height,
+    regions: maskRegionBoxes,
     touchesBottom,
     touchesLeft,
     touchesRight,
@@ -2733,6 +2811,7 @@ async function applyScaleAdjustPatchCompositeToImages(params: {
     debugLabel,
     featherPx,
     imageCount: mergedImages.length,
+    maskRegionCount: maskRegionBoxes?.length || 0,
     sourceHeight,
     sourceWidth,
     workspaceBox,